Refactoring listener app with configurable fallback (#3096)

Dockerfile

@@ -38,6 +38,7 @@ RUN --mount=target=. \
   export GOOS=${TARGETOS} GOARCH=${TARGETARCH} GOARM=${TARGETVARIANT#v} && \
   go build -trimpath -ldflags="-s -w -X 'github.com/actions/actions-runner-controller/build.Version=${VERSION}' -X 'github.com/actions/actions-runner-controller/build.CommitSHA=${COMMIT_SHA}'" -o /out/manager main.go && \
   go build -trimpath -ldflags="-s -w -X 'github.com/actions/actions-runner-controller/build.Version=${VERSION}' -X 'github.com/actions/actions-runner-controller/build.CommitSHA=${COMMIT_SHA}'" -o /out/github-runnerscaleset-listener ./cmd/githubrunnerscalesetlistener && \
+  go build -trimpath -ldflags="-s -w -X 'github.com/actions/actions-runner-controller/build.Version=${VERSION}' -X 'github.com/actions/actions-runner-controller/build.CommitSHA=${COMMIT_SHA}'" -o /out/ghalistener ./cmd/ghalistener && \
   go build -trimpath -ldflags="-s -w" -o /out/github-webhook-server ./cmd/githubwebhookserver && \
   go build -trimpath -ldflags="-s -w" -o /out/actions-metrics-server ./cmd/actionsmetricsserver && \
   go build -trimpath -ldflags="-s -w" -o /out/sleep ./cmd/sleep
@@ -52,6 +53,7 @@ COPY --from=builder /out/manager .
 COPY --from=builder /out/github-webhook-server .
 COPY --from=builder /out/actions-metrics-server .
 COPY --from=builder /out/github-runnerscaleset-listener .
+COPY --from=builder /out/ghalistener .
 COPY --from=builder /out/sleep .
 
 USER 65532:65532

cmd/ghalistener/app/app.go

@@ -0,0 +1,133 @@
+package app
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/actions/actions-runner-controller/cmd/ghalistener/config"
+	"github.com/actions/actions-runner-controller/cmd/ghalistener/listener"
+	"github.com/actions/actions-runner-controller/cmd/ghalistener/metrics"
+	"github.com/actions/actions-runner-controller/cmd/ghalistener/worker"
+	"github.com/actions/actions-runner-controller/github/actions"
+	"github.com/go-logr/logr"
+	"golang.org/x/sync/errgroup"
+)
+
+// App is responsible for initializing required components and running the app.
+type App struct {
+	// configured fields
+	config config.Config
+	logger logr.Logger
+
+	// initialized fields
+	listener Listener
+	worker   Worker
+	metrics  metrics.ServerPublisher
+}
+
+//go:generate mockery --name Listener --output ./mocks --outpkg mocks --case underscore
+type Listener interface {
+	Listen(ctx context.Context, handler listener.Handler) error
+}
+
+//go:generate mockery --name Worker --output ./mocks --outpkg mocks --case underscore
+type Worker interface {
+	HandleJobStarted(ctx context.Context, jobInfo *actions.JobStarted) error
+	HandleDesiredRunnerCount(ctx context.Context, desiredRunnerCount int) error
+}
+
+func New(config config.Config) (*App, error) {
+	app := &App{
+		config: config,
+	}
+
+	ghConfig, err := actions.ParseGitHubConfigFromURL(config.ConfigureUrl)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse GitHub config from URL: %w", err)
+	}
+
+	{
+		logger, err := config.Logger()
+		if err != nil {
+			return nil, fmt.Errorf("failed to create logger: %w", err)
+		}
+		app.logger = logger.WithName("listener-app")
+	}
+
+	actionsClient, err := config.ActionsClient(app.logger)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create actions client: %w", err)
+	}
+
+	if config.MetricsAddr != "" {
+		app.metrics = metrics.NewExporter(metrics.ExporterConfig{
+			ScaleSetName:      config.EphemeralRunnerSetName,
+			ScaleSetNamespace: config.EphemeralRunnerSetNamespace,
+			Enterprise:        ghConfig.Enterprise,
+			Organization:      ghConfig.Organization,
+			Repository:        ghConfig.Repository,
+			ServerAddr:        config.MetricsAddr,
+			ServerEndpoint:    config.MetricsEndpoint,
+		})
+	}
+
+	worker, err := worker.New(
+		worker.Config{
+			EphemeralRunnerSetNamespace: config.EphemeralRunnerSetNamespace,
+			EphemeralRunnerSetName:      config.EphemeralRunnerSetName,
+			MaxRunners:                  config.MaxRunners,
+			MinRunners:                  config.MinRunners,
+		},
+		worker.WithLogger(app.logger.WithName("worker")),
+	)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create new kubernetes worker: %w", err)
+	}
+	app.worker = worker
+
+	listener, err := listener.New(listener.Config{
+		Client:     actionsClient,
+		ScaleSetID: app.config.RunnerScaleSetId,
+		MinRunners: app.config.MinRunners,
+		MaxRunners: app.config.MaxRunners,
+		Logger:     app.logger.WithName("listener"),
+		Metrics:    app.metrics,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("failed to create new listener: %w", err)
+	}
+	app.listener = listener
+
+	app.logger.Info("app initialized")
+
+	return app, nil
+}
+
+func (app *App) Run(ctx context.Context) error {
+	var errs []error
+	if app.worker == nil {
+		errs = append(errs, fmt.Errorf("worker not initialized"))
+	}
+	if app.listener == nil {
+		errs = append(errs, fmt.Errorf("listener not initialized"))
+	}
+	if err := errors.Join(errs...); err != nil {
+		return fmt.Errorf("app not initialized: %w", err)
+	}
+
+	g, ctx := errgroup.WithContext(ctx)
+	g.Go(func() error {
+		app.logger.Info("Starting listener")
+		return app.listener.Listen(ctx, app.worker)
+	})
+
+	if app.metrics != nil {
+		g.Go(func() error {
+			app.logger.Info("Starting metrics server")
+			return app.metrics.ListenAndServe(ctx)
+		})
+	}
+
+	return g.Wait()
+}

cmd/ghalistener/app/app_test.go

@@ -0,0 +1,85 @@
+package app
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	appmocks "github.com/actions/actions-runner-controller/cmd/ghalistener/app/mocks"
+	"github.com/actions/actions-runner-controller/cmd/ghalistener/listener"
+	metricsMocks "github.com/actions/actions-runner-controller/cmd/ghalistener/metrics/mocks"
+	"github.com/actions/actions-runner-controller/cmd/ghalistener/worker"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/mock"
+)
+
+func TestApp_Run(t *testing.T) {
+	t.Parallel()
+
+	t.Run("ListenerWorkerGuard", func(t *testing.T) {
+		invalidApps := []*App{
+			{},
+			{worker: &worker.Worker{}},
+			{listener: &listener.Listener{}},
+		}
+
+		for _, app := range invalidApps {
+			assert.Error(t, app.Run(context.Background()))
+		}
+	})
+
+	t.Run("ExitsOnListenerError", func(t *testing.T) {
+		listener := appmocks.NewListener(t)
+		worker := appmocks.NewWorker(t)
+
+		listener.On("Listen", mock.Anything, mock.Anything).Return(errors.New("listener error")).Once()
+
+		app := &App{
+			listener: listener,
+			worker:   worker,
+		}
+
+		err := app.Run(context.Background())
+		assert.Error(t, err)
+	})
+
+	t.Run("ExitsOnListenerNil", func(t *testing.T) {
+		listener := appmocks.NewListener(t)
+		worker := appmocks.NewWorker(t)
+
+		listener.On("Listen", mock.Anything, mock.Anything).Return(nil).Once()
+
+		app := &App{
+			listener: listener,
+			worker:   worker,
+		}
+
+		err := app.Run(context.Background())
+		assert.NoError(t, err)
+	})
+
+	t.Run("CancelListenerOnMetricsServerError", func(t *testing.T) {
+		listener := appmocks.NewListener(t)
+		worker := appmocks.NewWorker(t)
+		metrics := metricsMocks.NewServerPublisher(t)
+		ctx := context.Background()
+
+		listener.On("Listen", mock.Anything, mock.Anything).Run(func(args mock.Arguments) {
+			ctx := args.Get(0).(context.Context)
+			go func() {
+				<-ctx.Done()
+			}()
+		}).Return(nil).Once()
+
+		metrics.On("ListenAndServe", mock.Anything).Return(errors.New("metrics server error")).Once()
+
+		app := &App{
+			listener: listener,
+			worker:   worker,
+			metrics:  metrics,
+		}
+
+		err := app.Run(ctx)
+		assert.Error(t, err)
+	})
+}

cmd/ghalistener/app/mocks/listener.go

@@ -0,0 +1,43 @@
+// Code generated by mockery v2.36.1. DO NOT EDIT.
+
+package mocks
+
+import (
+	context "context"
+
+	listener "github.com/actions/actions-runner-controller/cmd/ghalistener/listener"
+	mock "github.com/stretchr/testify/mock"
+)
+
+// Listener is an autogenerated mock type for the Listener type
+type Listener struct {
+	mock.Mock
+}
+
+// Listen provides a mock function with given fields: ctx, handler
+func (_m *Listener) Listen(ctx context.Context, handler listener.Handler) error {
+	ret := _m.Called(ctx, handler)
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(context.Context, listener.Handler) error); ok {
+		r0 = rf(ctx, handler)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
+// NewListener creates a new instance of Listener. It also registers a testing interface on the mock and a cleanup function to assert the mocks expectations.
+// The first argument is typically a *testing.T value.
+func NewListener(t interface {
+	mock.TestingT
+	Cleanup(func())
+}) *Listener {
+	mock := &Listener{}
+	mock.Mock.Test(t)
+
+	t.Cleanup(func() { mock.AssertExpectations(t) })
+
+	return mock
+}

cmd/ghalistener/app/mocks/worker.go

@@ -0,0 +1,58 @@
+// Code generated by mockery v2.36.1. DO NOT EDIT.
+
+package mocks
+
+import (
+	actions "github.com/actions/actions-runner-controller/github/actions"
+
+	context "context"
+
+	mock "github.com/stretchr/testify/mock"
+)
+
+// Worker is an autogenerated mock type for the Worker type
+type Worker struct {
+	mock.Mock
+}
+
+// HandleDesiredRunnerCount provides a mock function with given fields: ctx, desiredRunnerCount
+func (_m *Worker) HandleDesiredRunnerCount(ctx context.Context, desiredRunnerCount int) error {
+	ret := _m.Called(ctx, desiredRunnerCount)
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(context.Context, int) error); ok {
+		r0 = rf(ctx, desiredRunnerCount)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
+// HandleJobStarted provides a mock function with given fields: ctx, jobInfo
+func (_m *Worker) HandleJobStarted(ctx context.Context, jobInfo *actions.JobStarted) error {
+	ret := _m.Called(ctx, jobInfo)
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(context.Context, *actions.JobStarted) error); ok {
+		r0 = rf(ctx, jobInfo)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
+// NewWorker creates a new instance of Worker. It also registers a testing interface on the mock and a cleanup function to assert the mocks expectations.
+// The first argument is typically a *testing.T value.
+func NewWorker(t interface {
+	mock.TestingT
+	Cleanup(func())
+}) *Worker {
+	mock := &Worker{}
+	mock.Mock.Test(t)
+
+	t.Cleanup(func() { mock.AssertExpectations(t) })
+
+	return mock
+}

cmd/ghalistener/config/config.go

@@ -0,0 +1,147 @@
+package config
+
+import (
+	"crypto/x509"
+	"encoding/json"
+	"fmt"
+	"os"
+
+	"github.com/actions/actions-runner-controller/build"
+	"github.com/actions/actions-runner-controller/github/actions"
+	"github.com/actions/actions-runner-controller/logging"
+	"github.com/go-logr/logr"
+)
+
+type Config struct {
+	ConfigureUrl                string `json:"configureUrl"`
+	AppID                       int64  `json:"appID"`
+	AppInstallationID           int64  `json:"appInstallationID"`
+	AppPrivateKey               string `json:"appPrivateKey"`
+	Token                       string `json:"token"`
+	EphemeralRunnerSetNamespace string `json:"ephemeralRunnerSetNamespace"`
+	EphemeralRunnerSetName      string `json:"ephemeralRunnerSetName"`
+	MaxRunners                  int    `json:"maxRunners"`
+	MinRunners                  int    `json:"minRunners"`
+	RunnerScaleSetId            int    `json:"runnerScaleSetId"`
+	RunnerScaleSetName          string `json:"runnerScaleSetName"`
+	ServerRootCA                string `json:"serverRootCA"`
+	LogLevel                    string `json:"logLevel"`
+	LogFormat                   string `json:"logFormat"`
+	MetricsAddr                 string `json:"metricsAddr"`
+	MetricsEndpoint             string `json:"metricsEndpoint"`
+}
+
+func Read(path string) (Config, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return Config{}, err
+	}
+	defer f.Close()
+
+	var config Config
+	if err := json.NewDecoder(f).Decode(&config); err != nil {
+		return Config{}, fmt.Errorf("failed to decode config: %w", err)
+	}
+
+	if err := config.validate(); err != nil {
+		return Config{}, fmt.Errorf("failed to validate config: %w", err)
+	}
+
+	return config, nil
+}
+
+func (c *Config) validate() error {
+	if len(c.ConfigureUrl) == 0 {
+		return fmt.Errorf("GitHubConfigUrl is not provided")
+	}
+
+	if len(c.EphemeralRunnerSetNamespace) == 0 || len(c.EphemeralRunnerSetName) == 0 {
+		return fmt.Errorf("EphemeralRunnerSetNamespace '%s' or EphemeralRunnerSetName '%s' is missing", c.EphemeralRunnerSetNamespace, c.EphemeralRunnerSetName)
+	}
+
+	if c.RunnerScaleSetId == 0 {
+		return fmt.Errorf("RunnerScaleSetId '%d' is missing", c.RunnerScaleSetId)
+	}
+
+	if c.MaxRunners < c.MinRunners {
+		return fmt.Errorf("MinRunners '%d' cannot be greater than MaxRunners '%d'", c.MinRunners, c.MaxRunners)
+	}
+
+	hasToken := len(c.Token) > 0
+	hasPrivateKeyConfig := c.AppID > 0 && c.AppPrivateKey != ""
+
+	if !hasToken && !hasPrivateKeyConfig {
+		return fmt.Errorf("GitHub auth credential is missing, token length: '%d', appId: '%d', installationId: '%d', private key length: '%d", len(c.Token), c.AppID, c.AppInstallationID, len(c.AppPrivateKey))
+	}
+
+	if hasToken && hasPrivateKeyConfig {
+		return fmt.Errorf("only one GitHub auth method supported at a time. Have both PAT and App auth: token length: '%d', appId: '%d', installationId: '%d', private key length: '%d", len(c.Token), c.AppID, c.AppInstallationID, len(c.AppPrivateKey))
+	}
+
+	return nil
+}
+
+func (c *Config) Logger() (logr.Logger, error) {
+	logLevel := string(logging.LogLevelDebug)
+	if c.LogLevel != "" {
+		logLevel = c.LogLevel
+	}
+
+	logFormat := string(logging.LogFormatText)
+	if c.LogFormat != "" {
+		logFormat = c.LogFormat
+	}
+
+	logger, err := logging.NewLogger(logLevel, logFormat)
+	if err != nil {
+		return logr.Logger{}, fmt.Errorf("NewLogger failed: %w", err)
+	}
+
+	return logger, nil
+}
+
+func (c *Config) ActionsClient(logger logr.Logger) (*actions.Client, error) {
+
+	var creds actions.ActionsAuth
+	switch c.Token {
+	case "":
+		creds.AppCreds = &actions.GitHubAppAuth{
+			AppID:             c.AppID,
+			AppInstallationID: c.AppInstallationID,
+			AppPrivateKey:     c.AppPrivateKey,
+		}
+	default:
+		creds.Token = c.Token
+	}
+
+	options := []actions.ClientOption{
+		actions.WithLogger(logger),
+	}
+
+	if c.ServerRootCA != "" {
+		systemPool, err := x509.SystemCertPool()
+		if err != nil {
+			return nil, fmt.Errorf("failed to load system cert pool: %w", err)
+		}
+		pool := systemPool.Clone()
+		ok := pool.AppendCertsFromPEM([]byte(c.ServerRootCA))
+		if !ok {
+			return nil, fmt.Errorf("failed to parse root certificate")
+		}
+
+		options = append(options, actions.WithRootCAs(pool))
+	}
+
+	client, err := actions.NewClient(c.ConfigureUrl, &creds, options...)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create actions client: %w", err)
+	}
+
+	client.SetUserAgent(actions.UserAgentInfo{
+		Version:    build.Version,
+		CommitSHA:  build.CommitSHA,
+		ScaleSetID: c.RunnerScaleSetId,
+	})
+
+	return client, nil
+}

cmd/ghalistener/config/config_test.go

@@ -0,0 +1,92 @@
+package config
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestConfigValidationMinMax(t *testing.T) {
+	config := &Config{
+		ConfigureUrl:                "github.com/some_org/some_repo",
+		EphemeralRunnerSetNamespace: "namespace",
+		EphemeralRunnerSetName:      "deployment",
+		RunnerScaleSetId:            1,
+		MinRunners:                  5,
+		MaxRunners:                  2,
+		Token:                       "token",
+	}
+	err := config.validate()
+	assert.ErrorContains(t, err, "MinRunners '5' cannot be greater than MaxRunners '2", "Expected error about MinRunners > MaxRunners")
+}
+
+func TestConfigValidationMissingToken(t *testing.T) {
+	config := &Config{
+		ConfigureUrl:                "github.com/some_org/some_repo",
+		EphemeralRunnerSetNamespace: "namespace",
+		EphemeralRunnerSetName:      "deployment",
+		RunnerScaleSetId:            1,
+	}
+	err := config.validate()
+	expectedError := fmt.Sprintf("GitHub auth credential is missing, token length: '%d', appId: '%d', installationId: '%d', private key length: '%d", len(config.Token), config.AppID, config.AppInstallationID, len(config.AppPrivateKey))
+	assert.ErrorContains(t, err, expectedError, "Expected error about missing auth")
+}
+
+func TestConfigValidationAppKey(t *testing.T) {
+	config := &Config{
+		AppID:                       1,
+		AppInstallationID:           10,
+		ConfigureUrl:                "github.com/some_org/some_repo",
+		EphemeralRunnerSetNamespace: "namespace",
+		EphemeralRunnerSetName:      "deployment",
+		RunnerScaleSetId:            1,
+	}
+	err := config.validate()
+	expectedError := fmt.Sprintf("GitHub auth credential is missing, token length: '%d', appId: '%d', installationId: '%d', private key length: '%d", len(config.Token), config.AppID, config.AppInstallationID, len(config.AppPrivateKey))
+	assert.ErrorContains(t, err, expectedError, "Expected error about missing auth")
+}
+
+func TestConfigValidationOnlyOneTypeOfCredentials(t *testing.T) {
+	config := &Config{
+		AppID:                       1,
+		AppInstallationID:           10,
+		AppPrivateKey:               "asdf",
+		Token:                       "asdf",
+		ConfigureUrl:                "github.com/some_org/some_repo",
+		EphemeralRunnerSetNamespace: "namespace",
+		EphemeralRunnerSetName:      "deployment",
+		RunnerScaleSetId:            1,
+	}
+	err := config.validate()
+	expectedError := fmt.Sprintf("only one GitHub auth method supported at a time. Have both PAT and App auth: token length: '%d', appId: '%d', installationId: '%d', private key length: '%d", len(config.Token), config.AppID, config.AppInstallationID, len(config.AppPrivateKey))
+	assert.ErrorContains(t, err, expectedError, "Expected error about missing auth")
+}
+
+func TestConfigValidation(t *testing.T) {
+	config := &Config{
+		ConfigureUrl:                "https://github.com/actions",
+		EphemeralRunnerSetNamespace: "namespace",
+		EphemeralRunnerSetName:      "deployment",
+		RunnerScaleSetId:            1,
+		MinRunners:                  1,
+		MaxRunners:                  5,
+		Token:                       "asdf",
+	}
+
+	err := config.validate()
+
+	assert.NoError(t, err, "Expected no error")
+}
+
+func TestConfigValidationConfigUrl(t *testing.T) {
+	config := &Config{
+		EphemeralRunnerSetNamespace: "namespace",
+		EphemeralRunnerSetName:      "deployment",
+		RunnerScaleSetId:            1,
+	}
+
+	err := config.validate()
+
+	assert.ErrorContains(t, err, "GitHubConfigUrl is not provided", "Expected error about missing ConfigureUrl")
+}

cmd/ghalistener/listener/listener.go

@@ -0,0 +1,388 @@
+package listener
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"os"
+	"time"
+
+	"github.com/actions/actions-runner-controller/cmd/ghalistener/metrics"
+	"github.com/actions/actions-runner-controller/github/actions"
+	"github.com/go-logr/logr"
+	"github.com/google/uuid"
+)
+
+const (
+	sessionCreationMaxRetries = 10
+)
+
+// message types
+const (
+	messageTypeJobAvailable = "JobAvailable"
+	messageTypeJobAssigned  = "JobAssigned"
+	messageTypeJobStarted   = "JobStarted"
+	messageTypeJobCompleted = "JobCompleted"
+)
+
+//go:generate mockery --name Client --output ./mocks --outpkg mocks --case underscore
+type Client interface {
+	GetAcquirableJobs(ctx context.Context, runnerScaleSetId int) (*actions.AcquirableJobList, error)
+	CreateMessageSession(ctx context.Context, runnerScaleSetId int, owner string) (*actions.RunnerScaleSetSession, error)
+	GetMessage(ctx context.Context, messageQueueUrl, messageQueueAccessToken string, lastMessageId int64) (*actions.RunnerScaleSetMessage, error)
+	DeleteMessage(ctx context.Context, messageQueueUrl, messageQueueAccessToken string, messageId int64) error
+	AcquireJobs(ctx context.Context, runnerScaleSetId int, messageQueueAccessToken string, requestIds []int64) ([]int64, error)
+	RefreshMessageSession(ctx context.Context, runnerScaleSetId int, sessionId *uuid.UUID) (*actions.RunnerScaleSetSession, error)
+}
+
+type Config struct {
+	Client     Client
+	ScaleSetID int
+	MinRunners int
+	MaxRunners int
+	Logger     logr.Logger
+	Metrics    metrics.Publisher
+}
+
+func (c *Config) Validate() error {
+	if c.Client == nil {
+		return errors.New("client is required")
+	}
+	if c.ScaleSetID == 0 {
+		return errors.New("scaleSetID is required")
+	}
+	if c.MinRunners < 0 {
+		return errors.New("minRunners must be greater than or equal to 0")
+	}
+	if c.MaxRunners < 0 {
+		return errors.New("maxRunners must be greater than or equal to 0")
+	}
+	if c.MaxRunners > 0 && c.MinRunners > c.MaxRunners {
+		return errors.New("minRunners must be less than or equal to maxRunners")
+	}
+	return nil
+}
+
+// The Listener's role is to manage all interactions with the actions service.
+// It receives messages and processes them using the given handler.
+type Listener struct {
+	// configured fields
+	scaleSetID int               // The ID of the scale set associated with the listener.
+	client     Client            // The client used to interact with the scale set.
+	metrics    metrics.Publisher // The publisher used to publish metrics.
+
+	// internal fields
+	logger   logr.Logger // The logger used for logging.
+	hostname string      // The hostname of the listener.
+
+	// updated fields
+	lastMessageID int64                          // The ID of the last processed message.
+	session       *actions.RunnerScaleSetSession // The session for managing the runner scale set.
+}
+
+func New(config Config) (*Listener, error) {
+	if err := config.Validate(); err != nil {
+		return nil, fmt.Errorf("invalid config: %w", err)
+	}
+
+	listener := &Listener{
+		scaleSetID: config.ScaleSetID,
+		client:     config.Client,
+		logger:     config.Logger,
+		metrics:    metrics.Discard,
+	}
+
+	if config.Metrics != nil {
+		listener.metrics = config.Metrics
+	}
+
+	listener.metrics.PublishStatic(config.MinRunners, config.MaxRunners)
+
+	hostname, err := os.Hostname()
+	if err != nil {
+		hostname = uuid.NewString()
+		listener.logger.Info("Failed to get hostname, fallback to uuid", "uuid", hostname, "error", err)
+	}
+	listener.hostname = hostname
+
+	return listener, nil
+}
+
+//go:generate mockery --name Handler --output ./mocks --outpkg mocks --case underscore
+type Handler interface {
+	HandleJobStarted(ctx context.Context, jobInfo *actions.JobStarted) error
+	HandleDesiredRunnerCount(ctx context.Context, desiredRunnerCount int) error
+}
+
+// Listen listens for incoming messages and handles them using the provided handler.
+// It continuously listens for messages until the context is cancelled.
+// The initial message contains the current statistics and acquirable jobs, if any.
+// The handler is responsible for handling the initial message and subsequent messages.
+// If an error occurs during any step, Listen returns an error.
+func (l *Listener) Listen(ctx context.Context, handler Handler) error {
+	if err := l.createSession(ctx); err != nil {
+		return fmt.Errorf("createSession failed: %w", err)
+	}
+
+	initialMessage := &actions.RunnerScaleSetMessage{
+		MessageId:   0,
+		MessageType: "RunnerScaleSetJobMessages",
+		Statistics:  l.session.Statistics,
+		Body:        "",
+	}
+
+	if l.session.Statistics.TotalAvailableJobs > 0 || l.session.Statistics.TotalAssignedJobs > 0 {
+		acquirableJobs, err := l.client.GetAcquirableJobs(ctx, l.scaleSetID)
+		if err != nil {
+			return fmt.Errorf("failed to call GetAcquirableJobs: %w", err)
+		}
+
+		acquirableJobsJson, err := json.Marshal(acquirableJobs)
+		if err != nil {
+			return fmt.Errorf("failed to marshal acquirable jobs: %w", err)
+		}
+
+		initialMessage.Body = string(acquirableJobsJson)
+	}
+
+	if err := handler.HandleDesiredRunnerCount(ctx, initialMessage.Statistics.TotalAssignedJobs); err != nil {
+		return fmt.Errorf("handling initial message failed: %w", err)
+	}
+
+	for {
+		select {
+		case <-ctx.Done():
+			return fmt.Errorf("context cancelled: %w", ctx.Err())
+		default:
+		}
+
+		msg, err := l.getMessage(ctx)
+		if err != nil {
+			return fmt.Errorf("failed to get message: %w", err)
+		}
+
+		if msg == nil {
+			continue
+		}
+
+		statistics, jobsStarted, err := l.parseMessage(ctx, msg)
+		if err != nil {
+			return fmt.Errorf("failed to parse message: %w", err)
+		}
+
+		l.lastMessageID = msg.MessageId
+
+		if err := l.deleteLastMessage(ctx); err != nil {
+			return fmt.Errorf("failed to delete message: %w", err)
+		}
+
+		for _, jobStarted := range jobsStarted {
+			if err := handler.HandleJobStarted(ctx, jobStarted); err != nil {
+				return fmt.Errorf("failed to handle job started: %w", err)
+			}
+		}
+
+		if err := handler.HandleDesiredRunnerCount(ctx, statistics.TotalAssignedJobs); err != nil {
+			return fmt.Errorf("failed to handle desired runner count: %w", err)
+		}
+	}
+}
+
+func (l *Listener) createSession(ctx context.Context) error {
+	var session *actions.RunnerScaleSetSession
+	var retries int
+
+	for {
+		var err error
+		session, err = l.client.CreateMessageSession(ctx, l.scaleSetID, l.hostname)
+		if err == nil {
+			break
+		}
+
+		clientErr := &actions.HttpClientSideError{}
+		if !errors.As(err, &clientErr) {
+			return fmt.Errorf("failed to create session: %w", err)
+		}
+
+		if clientErr.Code != http.StatusConflict {
+			return fmt.Errorf("failed to create session: %w", err)
+		}
+
+		retries++
+		if retries >= sessionCreationMaxRetries {
+			return fmt.Errorf("failed to create session after %d retries: %w", retries, err)
+		}
+
+		l.logger.Info("Unable to create message session. Will try again in 30 seconds", "error", err.Error())
+
+		select {
+		case <-ctx.Done():
+			return fmt.Errorf("context cancelled: %w", ctx.Err())
+		case <-time.After(30 * time.Second):
+		}
+	}
+
+	statistics, err := json.Marshal(session.Statistics)
+	if err != nil {
+		return fmt.Errorf("failed to marshal statistics: %w", err)
+	}
+	l.logger.Info("Current runner scale set statistics.", "statistics", string(statistics))
+
+	l.session = session
+
+	return nil
+}
+
+func (l *Listener) getMessage(ctx context.Context) (*actions.RunnerScaleSetMessage, error) {
+	l.logger.Info("Getting next message", "lastMessageID", l.lastMessageID)
+	msg, err := l.client.GetMessage(ctx, l.session.MessageQueueUrl, l.session.MessageQueueAccessToken, l.lastMessageID)
+	if err == nil { // if NO error
+		return msg, nil
+	}
+
+	expiredError := &actions.MessageQueueTokenExpiredError{}
+	if !errors.As(err, &expiredError) {
+		return nil, fmt.Errorf("failed to get next message: %w", err)
+	}
+
+	if err := l.refreshSession(ctx); err != nil {
+		return nil, err
+	}
+
+	l.logger.Info("Getting next message", "lastMessageID", l.lastMessageID)
+
+	msg, err = l.client.GetMessage(ctx, l.session.MessageQueueUrl, l.session.MessageQueueAccessToken, l.lastMessageID)
+	if err != nil { // if NO error
+		return nil, fmt.Errorf("failed to get next message after message session refresh: %w", err)
+	}
+
+	return msg, nil
+
+}
+
+func (l *Listener) deleteLastMessage(ctx context.Context) error {
+	l.logger.Info("Deleting last message", "lastMessageID", l.lastMessageID)
+	if err := l.client.DeleteMessage(ctx, l.session.MessageQueueUrl, l.session.MessageQueueAccessToken, l.lastMessageID); err != nil {
+		return fmt.Errorf("failed to delete message: %w", err)
+	}
+
+	return nil
+}
+
+func (l *Listener) parseMessage(ctx context.Context, msg *actions.RunnerScaleSetMessage) (*actions.RunnerScaleSetStatistic, []*actions.JobStarted, error) {
+	l.logger.Info("Processing message", "messageId", msg.MessageId, "messageType", msg.MessageType)
+	if msg.Statistics == nil {
+		return nil, nil, fmt.Errorf("invalid message: statistics is nil")
+	}
+
+	l.logger.Info("New runner scale set statistics.", "statistics", msg.Statistics)
+
+	if msg.MessageType != "RunnerScaleSetJobMessages" {
+		l.logger.Info("Skipping message", "messageType", msg.MessageType)
+		return nil, nil, fmt.Errorf("invalid message type: %s", msg.MessageType)
+	}
+
+	var batchedMessages []json.RawMessage
+	if len(msg.Body) > 0 {
+		if err := json.Unmarshal([]byte(msg.Body), &batchedMessages); err != nil {
+			return nil, nil, fmt.Errorf("failed to unmarshal batched messages: %w", err)
+		}
+	}
+
+	var availableJobs []int64
+	var startedJobs []*actions.JobStarted
+	for _, msg := range batchedMessages {
+		var messageType actions.JobMessageType
+		if err := json.Unmarshal(msg, &messageType); err != nil {
+			return nil, nil, fmt.Errorf("failed to decode job message type: %w", err)
+		}
+
+		switch messageType.MessageType {
+		case messageTypeJobAvailable:
+			var jobAvailable actions.JobAvailable
+			if err := json.Unmarshal(msg, &jobAvailable); err != nil {
+				return nil, nil, fmt.Errorf("failed to decode job available: %w", err)
+			}
+
+			l.logger.Info("Job available message received", "jobId", jobAvailable.RunnerRequestId)
+			availableJobs = append(availableJobs, jobAvailable.RunnerRequestId)
+
+		case messageTypeJobAssigned:
+			var jobAssigned actions.JobAssigned
+			if err := json.Unmarshal(msg, &jobAssigned); err != nil {
+				return nil, nil, fmt.Errorf("failed to decode job assigned: %w", err)
+			}
+
+			l.logger.Info("Job assigned message received", "jobId", jobAssigned.RunnerRequestId)
+
+		case messageTypeJobStarted:
+			var jobStarted actions.JobStarted
+			if err := json.Unmarshal(msg, &jobStarted); err != nil {
+				return nil, nil, fmt.Errorf("could not decode job started message. %w", err)
+			}
+			l.logger.Info("Job started message received.", "RequestId", jobStarted.RunnerRequestId, "RunnerId", jobStarted.RunnerId)
+			startedJobs = append(startedJobs, &jobStarted)
+
+		case messageTypeJobCompleted:
+			var jobCompleted actions.JobCompleted
+			if err := json.Unmarshal(msg, &jobCompleted); err != nil {
+				return nil, nil, fmt.Errorf("failed to decode job completed: %w", err)
+			}
+
+			l.logger.Info("Job completed message received.", "RequestId", jobCompleted.RunnerRequestId, "Result", jobCompleted.Result, "RunnerId", jobCompleted.RunnerId, "RunnerName", jobCompleted.RunnerName)
+
+		default:
+			l.logger.Info("unknown job message type.", "messageType", messageType.MessageType)
+		}
+	}
+
+	l.logger.Info("Available jobs.", "count", len(availableJobs), "requestIds", fmt.Sprint(availableJobs))
+	if len(availableJobs) > 0 {
+		acquired, err := l.acquireAvailableJobs(ctx, availableJobs)
+		if err != nil {
+			return nil, nil, err
+		}
+
+		l.logger.Info("Jobs are acquired", "count", len(acquired), "requestIds", fmt.Sprint(acquired))
+	}
+
+	return msg.Statistics, startedJobs, nil
+}
+
+func (l *Listener) acquireAvailableJobs(ctx context.Context, availableJobs []int64) ([]int64, error) {
+	l.logger.Info("Acquiring jobs")
+
+	ids, err := l.client.AcquireJobs(ctx, l.scaleSetID, l.session.MessageQueueAccessToken, availableJobs)
+	if err == nil { // if NO errors
+		return ids, nil
+	}
+
+	expiredError := &actions.MessageQueueTokenExpiredError{}
+	if !errors.As(err, &expiredError) {
+		return nil, fmt.Errorf("failed to acquire jobs: %w", err)
+	}
+
+	if err := l.refreshSession(ctx); err != nil {
+		return nil, err
+	}
+
+	ids, err = l.client.AcquireJobs(ctx, l.scaleSetID, l.session.MessageQueueAccessToken, availableJobs)
+	if err != nil {
+		return nil, fmt.Errorf("failed to acquire jobs after session refresh: %w", err)
+	}
+
+	return ids, nil
+}
+
+func (l *Listener) refreshSession(ctx context.Context) error {
+	l.logger.Info("Message queue token is expired during GetNextMessage, refreshing...")
+	session, err := l.client.RefreshMessageSession(ctx, l.session.RunnerScaleSet.Id, l.session.SessionId)
+	if err != nil {
+		return fmt.Errorf("refresh message session failed. %w", err)
+	}
+
+	l.session = session
+	return nil
+}

cmd/ghalistener/listener/listener_test.go

@@ -0,0 +1,613 @@
+package listener
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"testing"
+	"time"
+
+	listenermocks "github.com/actions/actions-runner-controller/cmd/ghalistener/listener/mocks"
+	"github.com/actions/actions-runner-controller/cmd/ghalistener/metrics"
+	metricsmocks "github.com/actions/actions-runner-controller/cmd/ghalistener/metrics/mocks"
+	"github.com/actions/actions-runner-controller/github/actions"
+	"github.com/google/uuid"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNew(t *testing.T) {
+	t.Parallel()
+	t.Run("InvalidConfig", func(t *testing.T) {
+		t.Parallel()
+		var config Config
+		_, err := New(config)
+		assert.NotNil(t, err)
+	})
+
+	t.Run("ValidConfig", func(t *testing.T) {
+		t.Parallel()
+		config := Config{
+			Client:     listenermocks.NewClient(t),
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+		l, err := New(config)
+		assert.Nil(t, err)
+		assert.NotNil(t, l)
+	})
+
+	t.Run("SetStaticMetrics", func(t *testing.T) {
+		t.Parallel()
+
+		metrics := metricsmocks.NewPublisher(t)
+
+		metrics.On("PublishStatic", mock.Anything, mock.Anything).Once()
+
+		config := Config{
+			Client:     listenermocks.NewClient(t),
+			ScaleSetID: 1,
+			Metrics:    metrics,
+		}
+		l, err := New(config)
+		assert.Nil(t, err)
+		assert.NotNil(t, l)
+	})
+}
+
+func TestListener_createSession(t *testing.T) {
+	t.Parallel()
+	t.Run("FailOnce", func(t *testing.T) {
+		t.Parallel()
+		ctx := context.Background()
+
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+		client.On("CreateMessageSession", ctx, mock.Anything, mock.Anything).Return(nil, assert.AnError).Once()
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		err = l.createSession(ctx)
+		assert.NotNil(t, err)
+	})
+
+	t.Run("FailContext", func(t *testing.T) {
+		t.Parallel()
+		ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+		defer cancel()
+
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+		client.On("CreateMessageSession", ctx, mock.Anything, mock.Anything).Return(nil,
+			&actions.HttpClientSideError{Code: http.StatusConflict}).Once()
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		err = l.createSession(ctx)
+		assert.True(t, errors.Is(err, context.DeadlineExceeded))
+	})
+
+	t.Run("SetsSession", func(t *testing.T) {
+		t.Parallel()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+
+		uuid := uuid.New()
+		session := &actions.RunnerScaleSetSession{
+			SessionId:               &uuid,
+			OwnerName:               "example",
+			RunnerScaleSet:          &actions.RunnerScaleSet{},
+			MessageQueueUrl:         "https://example.com",
+			MessageQueueAccessToken: "1234567890",
+			Statistics:              nil,
+		}
+		client.On("CreateMessageSession", mock.Anything, mock.Anything, mock.Anything).Return(session, nil).Once()
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		err = l.createSession(context.Background())
+		assert.Nil(t, err)
+		assert.Equal(t, session, l.session)
+	})
+}
+
+func TestListener_getMessage(t *testing.T) {
+	t.Parallel()
+
+	t.Run("ReceivesMessage", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := context.Background()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+		want := &actions.RunnerScaleSetMessage{
+			MessageId: 1,
+		}
+		client.On("GetMessage", ctx, mock.Anything, mock.Anything, mock.Anything).Return(want, nil).Once()
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+		l.session = &actions.RunnerScaleSetSession{}
+
+		got, err := l.getMessage(ctx)
+		assert.Nil(t, err)
+		assert.Equal(t, want, got)
+	})
+
+	t.Run("NotExpiredError", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := context.Background()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+		client.On("GetMessage", ctx, mock.Anything, mock.Anything, mock.Anything).Return(nil, &actions.HttpClientSideError{Code: http.StatusNotFound}).Once()
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		l.session = &actions.RunnerScaleSetSession{}
+
+		_, err = l.getMessage(ctx)
+		assert.NotNil(t, err)
+	})
+
+	t.Run("RefreshAndSucceeds", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := context.Background()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+
+		uuid := uuid.New()
+		session := &actions.RunnerScaleSetSession{
+			SessionId:               &uuid,
+			OwnerName:               "example",
+			RunnerScaleSet:          &actions.RunnerScaleSet{},
+			MessageQueueUrl:         "https://example.com",
+			MessageQueueAccessToken: "1234567890",
+			Statistics:              nil,
+		}
+		client.On("RefreshMessageSession", ctx, mock.Anything, mock.Anything).Return(session, nil).Once()
+
+		client.On("GetMessage", ctx, mock.Anything, mock.Anything, mock.Anything).Return(nil, &actions.MessageQueueTokenExpiredError{}).Once()
+
+		want := &actions.RunnerScaleSetMessage{
+			MessageId: 1,
+		}
+		client.On("GetMessage", ctx, mock.Anything, mock.Anything, mock.Anything).Return(want, nil).Once()
+
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		l.session = &actions.RunnerScaleSetSession{
+			SessionId:      &uuid,
+			RunnerScaleSet: &actions.RunnerScaleSet{},
+		}
+
+		got, err := l.getMessage(ctx)
+		assert.Nil(t, err)
+		assert.Equal(t, want, got)
+	})
+
+	t.Run("RefreshAndFails", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := context.Background()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+
+		uuid := uuid.New()
+		session := &actions.RunnerScaleSetSession{
+			SessionId:               &uuid,
+			OwnerName:               "example",
+			RunnerScaleSet:          &actions.RunnerScaleSet{},
+			MessageQueueUrl:         "https://example.com",
+			MessageQueueAccessToken: "1234567890",
+			Statistics:              nil,
+		}
+		client.On("RefreshMessageSession", ctx, mock.Anything, mock.Anything).Return(session, nil).Once()
+
+		client.On("GetMessage", ctx, mock.Anything, mock.Anything, mock.Anything).Return(nil, &actions.MessageQueueTokenExpiredError{}).Twice()
+
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		l.session = &actions.RunnerScaleSetSession{
+			SessionId:      &uuid,
+			RunnerScaleSet: &actions.RunnerScaleSet{},
+		}
+
+		got, err := l.getMessage(ctx)
+		assert.NotNil(t, err)
+		assert.Nil(t, got)
+	})
+}
+
+func TestListener_refreshSession(t *testing.T) {
+	t.Parallel()
+
+	t.Run("SuccessfullyRefreshes", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := context.Background()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+
+		newUUID := uuid.New()
+		session := &actions.RunnerScaleSetSession{
+			SessionId:               &newUUID,
+			OwnerName:               "example",
+			RunnerScaleSet:          &actions.RunnerScaleSet{},
+			MessageQueueUrl:         "https://example.com",
+			MessageQueueAccessToken: "1234567890",
+			Statistics:              nil,
+		}
+		client.On("RefreshMessageSession", ctx, mock.Anything, mock.Anything).Return(session, nil).Once()
+
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		oldUUID := uuid.New()
+		l.session = &actions.RunnerScaleSetSession{
+			SessionId:      &oldUUID,
+			RunnerScaleSet: &actions.RunnerScaleSet{},
+		}
+
+		err = l.refreshSession(ctx)
+		assert.Nil(t, err)
+		assert.Equal(t, session, l.session)
+	})
+
+	t.Run("FailsToRefresh", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := context.Background()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+
+		client.On("RefreshMessageSession", ctx, mock.Anything, mock.Anything).Return(nil, errors.New("error")).Once()
+
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		oldUUID := uuid.New()
+		oldSession := &actions.RunnerScaleSetSession{
+			SessionId:      &oldUUID,
+			RunnerScaleSet: &actions.RunnerScaleSet{},
+		}
+		l.session = oldSession
+
+		err = l.refreshSession(ctx)
+		assert.NotNil(t, err)
+		assert.Equal(t, oldSession, l.session)
+	})
+}
+
+func TestListener_deleteLastMessage(t *testing.T) {
+	t.Parallel()
+
+	t.Run("SuccessfullyDeletes", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := context.Background()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+
+		client.On("DeleteMessage", ctx, mock.Anything, mock.Anything, mock.MatchedBy(func(lastMessageID any) bool {
+			return lastMessageID.(int64) == int64(5)
+		})).Return(nil).Once()
+
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		l.session = &actions.RunnerScaleSetSession{}
+		l.lastMessageID = 5
+
+		err = l.deleteLastMessage(ctx)
+		assert.Nil(t, err)
+	})
+
+	t.Run("FailsToDelete", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := context.Background()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+
+		client.On("DeleteMessage", ctx, mock.Anything, mock.Anything, mock.Anything).Return(errors.New("error")).Once()
+
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		l.session = &actions.RunnerScaleSetSession{}
+		l.lastMessageID = 5
+
+		err = l.deleteLastMessage(ctx)
+		assert.NotNil(t, err)
+	})
+}
+
+func TestListener_Listen(t *testing.T) {
+	t.Parallel()
+
+	t.Run("CreateSessionFails", func(t *testing.T) {
+		t.Parallel()
+		ctx := context.Background()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+		client.On("CreateMessageSession", ctx, mock.Anything, mock.Anything).Return(nil, assert.AnError).Once()
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		err = l.Listen(ctx, nil)
+		assert.NotNil(t, err)
+	})
+
+	t.Run("CallHandleRegardlessOfInitialMessage", func(t *testing.T) {
+		t.Parallel()
+		ctx, cancel := context.WithCancel(context.Background())
+
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+
+		uuid := uuid.New()
+		session := &actions.RunnerScaleSetSession{
+			SessionId:               &uuid,
+			OwnerName:               "example",
+			RunnerScaleSet:          &actions.RunnerScaleSet{},
+			MessageQueueUrl:         "https://example.com",
+			MessageQueueAccessToken: "1234567890",
+			Statistics:              &actions.RunnerScaleSetStatistic{},
+		}
+		client.On("CreateMessageSession", ctx, mock.Anything, mock.Anything).Return(session, nil).Once()
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		var called bool
+		handler := listenermocks.NewHandler(t)
+		handler.On("HandleDesiredRunnerCount", mock.Anything, mock.Anything).
+			Return(nil).
+			Run(
+				func(mock.Arguments) {
+					called = true
+					cancel()
+				},
+			).
+			Once()
+
+		err = l.Listen(ctx, handler)
+		assert.True(t, errors.Is(err, context.Canceled))
+		assert.True(t, called)
+	})
+}
+
+func TestListener_acquireAvailableJobs(t *testing.T) {
+	t.Parallel()
+
+	t.Run("FailingToAcquireJobs", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := context.Background()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+
+		client.On("AcquireJobs", ctx, mock.Anything, mock.Anything, mock.Anything).Return(nil, assert.AnError).Once()
+
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		uuid := uuid.New()
+		l.session = &actions.RunnerScaleSetSession{
+			SessionId:               &uuid,
+			OwnerName:               "example",
+			RunnerScaleSet:          &actions.RunnerScaleSet{},
+			MessageQueueUrl:         "https://example.com",
+			MessageQueueAccessToken: "1234567890",
+			Statistics:              &actions.RunnerScaleSetStatistic{},
+		}
+
+		_, err = l.acquireAvailableJobs(ctx, []int64{1, 2, 3})
+		assert.Error(t, err)
+	})
+
+	t.Run("SuccessfullyAcquiresJobsOnFirstRun", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := context.Background()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+
+		jobIDs := []int64{1, 2, 3}
+
+		client.On("AcquireJobs", ctx, mock.Anything, mock.Anything, mock.Anything).Return(jobIDs, nil).Once()
+
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		uuid := uuid.New()
+		l.session = &actions.RunnerScaleSetSession{
+			SessionId:               &uuid,
+			OwnerName:               "example",
+			RunnerScaleSet:          &actions.RunnerScaleSet{},
+			MessageQueueUrl:         "https://example.com",
+			MessageQueueAccessToken: "1234567890",
+			Statistics:              &actions.RunnerScaleSetStatistic{},
+		}
+
+		acquiredJobIDs, err := l.acquireAvailableJobs(ctx, []int64{1, 2, 3})
+		assert.NoError(t, err)
+		assert.Equal(t, jobIDs, acquiredJobIDs)
+	})
+
+	t.Run("RefreshAndSucceeds", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := context.Background()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+
+		uuid := uuid.New()
+		session := &actions.RunnerScaleSetSession{
+			SessionId:               &uuid,
+			OwnerName:               "example",
+			RunnerScaleSet:          &actions.RunnerScaleSet{},
+			MessageQueueUrl:         "https://example.com",
+			MessageQueueAccessToken: "1234567890",
+			Statistics:              nil,
+		}
+		client.On("RefreshMessageSession", ctx, mock.Anything, mock.Anything).Return(session, nil).Once()
+
+		// First call to AcquireJobs will fail with a token expired error
+		client.On("AcquireJobs", ctx, mock.Anything, mock.Anything, mock.Anything).Return(nil, &actions.MessageQueueTokenExpiredError{}).Once()
+
+		// Second call to AcquireJobs will succeed
+		want := []int64{1, 2, 3}
+		client.On("AcquireJobs", ctx, mock.Anything, mock.Anything, mock.Anything).Return(want, nil).Once()
+
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		l.session = &actions.RunnerScaleSetSession{
+			SessionId:      &uuid,
+			RunnerScaleSet: &actions.RunnerScaleSet{},
+		}
+
+		got, err := l.acquireAvailableJobs(ctx, want)
+		assert.Nil(t, err)
+		assert.Equal(t, want, got)
+	})
+
+	t.Run("RefreshAndFails", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := context.Background()
+		config := Config{
+			ScaleSetID: 1,
+			Metrics:    metrics.Discard,
+		}
+
+		client := listenermocks.NewClient(t)
+
+		uuid := uuid.New()
+		session := &actions.RunnerScaleSetSession{
+			SessionId:               &uuid,
+			OwnerName:               "example",
+			RunnerScaleSet:          &actions.RunnerScaleSet{},
+			MessageQueueUrl:         "https://example.com",
+			MessageQueueAccessToken: "1234567890",
+			Statistics:              nil,
+		}
+		client.On("RefreshMessageSession", ctx, mock.Anything, mock.Anything).Return(session, nil).Once()
+
+		client.On("AcquireJobs", ctx, mock.Anything, mock.Anything, mock.Anything).Return(nil, &actions.MessageQueueTokenExpiredError{}).Twice()
+
+		config.Client = client
+
+		l, err := New(config)
+		require.Nil(t, err)
+
+		l.session = &actions.RunnerScaleSetSession{
+			SessionId:      &uuid,
+			RunnerScaleSet: &actions.RunnerScaleSet{},
+		}
+
+		got, err := l.acquireAvailableJobs(ctx, []int64{1, 2, 3})
+		assert.NotNil(t, err)
+		assert.Nil(t, got)
+	})
+}

cmd/ghalistener/listener/mocks/client.go

@@ -0,0 +1,176 @@
+// Code generated by mockery v2.36.1. DO NOT EDIT.
+
+package mocks
+
+import (
+	context "context"
+
+	actions "github.com/actions/actions-runner-controller/github/actions"
+
+	mock "github.com/stretchr/testify/mock"
+
+	uuid "github.com/google/uuid"
+)
+
+// Client is an autogenerated mock type for the Client type
+type Client struct {
+	mock.Mock
+}
+
+// AcquireJobs provides a mock function with given fields: ctx, runnerScaleSetId, messageQueueAccessToken, requestIds
+func (_m *Client) AcquireJobs(ctx context.Context, runnerScaleSetId int, messageQueueAccessToken string, requestIds []int64) ([]int64, error) {
+	ret := _m.Called(ctx, runnerScaleSetId, messageQueueAccessToken, requestIds)
+
+	var r0 []int64
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, int, string, []int64) ([]int64, error)); ok {
+		return rf(ctx, runnerScaleSetId, messageQueueAccessToken, requestIds)
+	}
+	if rf, ok := ret.Get(0).(func(context.Context, int, string, []int64) []int64); ok {
+		r0 = rf(ctx, runnerScaleSetId, messageQueueAccessToken, requestIds)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).([]int64)
+		}
+	}
+
+	if rf, ok := ret.Get(1).(func(context.Context, int, string, []int64) error); ok {
+		r1 = rf(ctx, runnerScaleSetId, messageQueueAccessToken, requestIds)
+	} else {
+		r1 = ret.Error(1)
+	}
+
+	return r0, r1
+}
+
+// CreateMessageSession provides a mock function with given fields: ctx, runnerScaleSetId, owner
+func (_m *Client) CreateMessageSession(ctx context.Context, runnerScaleSetId int, owner string) (*actions.RunnerScaleSetSession, error) {
+	ret := _m.Called(ctx, runnerScaleSetId, owner)
+
+	var r0 *actions.RunnerScaleSetSession
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, int, string) (*actions.RunnerScaleSetSession, error)); ok {
+		return rf(ctx, runnerScaleSetId, owner)
+	}
+	if rf, ok := ret.Get(0).(func(context.Context, int, string) *actions.RunnerScaleSetSession); ok {
+		r0 = rf(ctx, runnerScaleSetId, owner)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(*actions.RunnerScaleSetSession)
+		}
+	}
+
+	if rf, ok := ret.Get(1).(func(context.Context, int, string) error); ok {
+		r1 = rf(ctx, runnerScaleSetId, owner)
+	} else {
+		r1 = ret.Error(1)
+	}
+
+	return r0, r1
+}
+
+// DeleteMessage provides a mock function with given fields: ctx, messageQueueUrl, messageQueueAccessToken, messageId
+func (_m *Client) DeleteMessage(ctx context.Context, messageQueueUrl string, messageQueueAccessToken string, messageId int64) error {
+	ret := _m.Called(ctx, messageQueueUrl, messageQueueAccessToken, messageId)
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(context.Context, string, string, int64) error); ok {
+		r0 = rf(ctx, messageQueueUrl, messageQueueAccessToken, messageId)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
+// GetAcquirableJobs provides a mock function with given fields: ctx, runnerScaleSetId
+func (_m *Client) GetAcquirableJobs(ctx context.Context, runnerScaleSetId int) (*actions.AcquirableJobList, error) {
+	ret := _m.Called(ctx, runnerScaleSetId)
+
+	var r0 *actions.AcquirableJobList
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, int) (*actions.AcquirableJobList, error)); ok {
+		return rf(ctx, runnerScaleSetId)
+	}
+	if rf, ok := ret.Get(0).(func(context.Context, int) *actions.AcquirableJobList); ok {
+		r0 = rf(ctx, runnerScaleSetId)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(*actions.AcquirableJobList)
+		}
+	}
+
+	if rf, ok := ret.Get(1).(func(context.Context, int) error); ok {
+		r1 = rf(ctx, runnerScaleSetId)
+	} else {
+		r1 = ret.Error(1)
+	}
+
+	return r0, r1
+}
+
+// GetMessage provides a mock function with given fields: ctx, messageQueueUrl, messageQueueAccessToken, lastMessageId
+func (_m *Client) GetMessage(ctx context.Context, messageQueueUrl string, messageQueueAccessToken string, lastMessageId int64) (*actions.RunnerScaleSetMessage, error) {
+	ret := _m.Called(ctx, messageQueueUrl, messageQueueAccessToken, lastMessageId)
+
+	var r0 *actions.RunnerScaleSetMessage
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, string, string, int64) (*actions.RunnerScaleSetMessage, error)); ok {
+		return rf(ctx, messageQueueUrl, messageQueueAccessToken, lastMessageId)
+	}
+	if rf, ok := ret.Get(0).(func(context.Context, string, string, int64) *actions.RunnerScaleSetMessage); ok {
+		r0 = rf(ctx, messageQueueUrl, messageQueueAccessToken, lastMessageId)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(*actions.RunnerScaleSetMessage)
+		}
+	}
+
+	if rf, ok := ret.Get(1).(func(context.Context, string, string, int64) error); ok {
+		r1 = rf(ctx, messageQueueUrl, messageQueueAccessToken, lastMessageId)
+	} else {
+		r1 = ret.Error(1)
+	}
+
+	return r0, r1
+}
+
+// RefreshMessageSession provides a mock function with given fields: ctx, runnerScaleSetId, sessionId
+func (_m *Client) RefreshMessageSession(ctx context.Context, runnerScaleSetId int, sessionId *uuid.UUID) (*actions.RunnerScaleSetSession, error) {
+	ret := _m.Called(ctx, runnerScaleSetId, sessionId)
+
+	var r0 *actions.RunnerScaleSetSession
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, int, *uuid.UUID) (*actions.RunnerScaleSetSession, error)); ok {
+		return rf(ctx, runnerScaleSetId, sessionId)
+	}
+	if rf, ok := ret.Get(0).(func(context.Context, int, *uuid.UUID) *actions.RunnerScaleSetSession); ok {
+		r0 = rf(ctx, runnerScaleSetId, sessionId)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(*actions.RunnerScaleSetSession)
+		}
+	}
+
+	if rf, ok := ret.Get(1).(func(context.Context, int, *uuid.UUID) error); ok {
+		r1 = rf(ctx, runnerScaleSetId, sessionId)
+	} else {
+		r1 = ret.Error(1)
+	}
+
+	return r0, r1
+}
+
+// NewClient creates a new instance of Client. It also registers a testing interface on the mock and a cleanup function to assert the mocks expectations.
+// The first argument is typically a *testing.T value.
+func NewClient(t interface {
+	mock.TestingT
+	Cleanup(func())
+}) *Client {
+	mock := &Client{}
+	mock.Mock.Test(t)
+
+	t.Cleanup(func() { mock.AssertExpectations(t) })
+
+	return mock
+}

cmd/ghalistener/listener/mocks/handler.go

@@ -0,0 +1,58 @@
+// Code generated by mockery v2.36.1. DO NOT EDIT.
+
+package mocks
+
+import (
+	context "context"
+
+	actions "github.com/actions/actions-runner-controller/github/actions"
+
+	mock "github.com/stretchr/testify/mock"
+)
+
+// Handler is an autogenerated mock type for the Handler type
+type Handler struct {
+	mock.Mock
+}
+
+// HandleDesiredRunnerCount provides a mock function with given fields: ctx, desiredRunnerCount
+func (_m *Handler) HandleDesiredRunnerCount(ctx context.Context, desiredRunnerCount int) error {
+	ret := _m.Called(ctx, desiredRunnerCount)
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(context.Context, int) error); ok {
+		r0 = rf(ctx, desiredRunnerCount)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
+// HandleJobStarted provides a mock function with given fields: ctx, jobInfo
+func (_m *Handler) HandleJobStarted(ctx context.Context, jobInfo *actions.JobStarted) error {
+	ret := _m.Called(ctx, jobInfo)
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(context.Context, *actions.JobStarted) error); ok {
+		r0 = rf(ctx, jobInfo)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
+// NewHandler creates a new instance of Handler. It also registers a testing interface on the mock and a cleanup function to assert the mocks expectations.
+// The first argument is typically a *testing.T value.
+func NewHandler(t interface {
+	mock.TestingT
+	Cleanup(func())
+}) *Handler {
+	mock := &Handler{}
+	mock.Mock.Test(t)
+
+	t.Cleanup(func() { mock.AssertExpectations(t) })
+
+	return mock
+}

cmd/ghalistener/main.go

@@ -0,0 +1,40 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"github.com/actions/actions-runner-controller/cmd/ghalistener/app"
+	"github.com/actions/actions-runner-controller/cmd/ghalistener/config"
+)
+
+func main() {
+	configPath, ok := os.LookupEnv("LISTENER_CONFIG_PATH")
+	if !ok {
+		fmt.Fprintf(os.Stderr, "Error: LISTENER_CONFIG_PATH environment variable is not set\n")
+		os.Exit(1)
+	}
+	config, err := config.Read(configPath)
+	if err != nil {
+		log.Printf("Failed to read config: %v", err)
+		os.Exit(1)
+	}
+
+	app, err := app.New(config)
+	if err != nil {
+		log.Printf("Failed to initialize app: %v", err)
+		os.Exit(1)
+	}
+
+	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
+	defer stop()
+
+	if err := app.Run(ctx); err != nil {
+		log.Printf("Application returned an error: %v", err)
+		os.Exit(1)
+	}
+}

cmd/ghalistener/metrics/metrics.go

@@ -0,0 +1,387 @@
+package metrics
+
+import (
+	"context"
+	"net/http"
+	"strconv"
+
+	"github.com/actions/actions-runner-controller/github/actions"
+	"github.com/go-logr/logr"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+const (
+	labelKeyRunnerScaleSetName      = "name"
+	labelKeyRunnerScaleSetNamespace = "namespace"
+	labelKeyEnterprise              = "enterprise"
+	labelKeyOrganization            = "organization"
+	labelKeyRepository              = "repository"
+	labelKeyJobName                 = "job_name"
+	labelKeyJobWorkflowRef          = "job_workflow_ref"
+	labelKeyEventName               = "event_name"
+	labelKeyJobResult               = "job_result"
+	labelKeyRunnerID                = "runner_id"
+	labelKeyRunnerName              = "runner_name"
+)
+
+const githubScaleSetSubsystem = "gha"
+
+// labels
+var (
+	scaleSetLabels = []string{
+		labelKeyRunnerScaleSetName,
+		labelKeyRepository,
+		labelKeyOrganization,
+		labelKeyEnterprise,
+		labelKeyRunnerScaleSetNamespace,
+	}
+
+	jobLabels = []string{
+		labelKeyRepository,
+		labelKeyOrganization,
+		labelKeyEnterprise,
+		labelKeyJobName,
+		labelKeyJobWorkflowRef,
+		labelKeyEventName,
+	}
+
+	completedJobsTotalLabels   = append(jobLabels, labelKeyJobResult, labelKeyRunnerID, labelKeyRunnerName)
+	jobExecutionDurationLabels = append(jobLabels, labelKeyJobResult, labelKeyRunnerID, labelKeyRunnerName)
+	startedJobsTotalLabels     = append(jobLabels, labelKeyRunnerID, labelKeyRunnerName)
+	jobStartupDurationLabels   = append(jobLabels, labelKeyRunnerID, labelKeyRunnerName)
+)
+
+var (
+	assignedJobs = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Subsystem: githubScaleSetSubsystem,
+			Name:      "assigned_jobs",
+			Help:      "Number of jobs assigned to this scale set.",
+		},
+		scaleSetLabels,
+	)
+
+	runningJobs = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Subsystem: githubScaleSetSubsystem,
+			Name:      "running_jobs",
+			Help:      "Number of jobs running (or about to be run).",
+		},
+		scaleSetLabels,
+	)
+
+	registeredRunners = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Subsystem: githubScaleSetSubsystem,
+			Name:      "registered_runners",
+			Help:      "Number of runners registered by the scale set.",
+		},
+		scaleSetLabels,
+	)
+
+	busyRunners = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Subsystem: githubScaleSetSubsystem,
+			Name:      "busy_runners",
+			Help:      "Number of registered runners running a job.",
+		},
+		scaleSetLabels,
+	)
+
+	minRunners = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Subsystem: githubScaleSetSubsystem,
+			Name:      "min_runners",
+			Help:      "Minimum number of runners.",
+		},
+		scaleSetLabels,
+	)
+
+	maxRunners = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Subsystem: githubScaleSetSubsystem,
+			Name:      "max_runners",
+			Help:      "Maximum number of runners.",
+		},
+		scaleSetLabels,
+	)
+
+	desiredRunners = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Subsystem: githubScaleSetSubsystem,
+			Name:      "desired_runners",
+			Help:      "Number of runners desired by the scale set.",
+		},
+		scaleSetLabels,
+	)
+
+	idleRunners = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Subsystem: githubScaleSetSubsystem,
+			Name:      "idle_runners",
+			Help:      "Number of registered runners not running a job.",
+		},
+		scaleSetLabels,
+	)
+
+	startedJobsTotal = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Subsystem: githubScaleSetSubsystem,
+			Name:      "started_jobs_total",
+			Help:      "Total number of jobs started.",
+		},
+		startedJobsTotalLabels,
+	)
+
+	completedJobsTotal = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name:      "completed_jobs_total",
+			Help:      "Total number of jobs completed.",
+			Subsystem: githubScaleSetSubsystem,
+		},
+		completedJobsTotalLabels,
+	)
+
+	jobStartupDurationSeconds = prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Subsystem: githubScaleSetSubsystem,
+			Name:      "job_startup_duration_seconds",
+			Help:      "Time spent waiting for workflow job to get started on the runner owned by the scale set (in seconds).",
+			Buckets:   runtimeBuckets,
+		},
+		jobStartupDurationLabels,
+	)
+
+	jobExecutionDurationSeconds = prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Subsystem: githubScaleSetSubsystem,
+			Name:      "job_execution_duration_seconds",
+			Help:      "Time spent executing workflow jobs by the scale set (in seconds).",
+			Buckets:   runtimeBuckets,
+		},
+		jobExecutionDurationLabels,
+	)
+)
+
+var runtimeBuckets []float64 = []float64{
+	0.01,
+	0.05,
+	0.1,
+	0.5,
+	1,
+	2,
+	3,
+	4,
+	5,
+	6,
+	7,
+	8,
+	9,
+	10,
+	12,
+	15,
+	18,
+	20,
+	25,
+	30,
+	40,
+	50,
+	60,
+	70,
+	80,
+	90,
+	100,
+	110,
+	120,
+	150,
+	180,
+	210,
+	240,
+	300,
+	360,
+	420,
+	480,
+	540,
+	600,
+	900,
+	1200,
+	1800,
+	2400,
+	3000,
+	3600,
+}
+
+type baseLabels struct {
+	scaleSetName      string
+	scaleSetNamespace string
+	enterprise        string
+	organization      string
+	repository        string
+}
+
+func (b *baseLabels) jobLabels(jobBase *actions.JobMessageBase) prometheus.Labels {
+	return prometheus.Labels{
+		labelKeyEnterprise:     b.enterprise,
+		labelKeyOrganization:   b.organization,
+		labelKeyRepository:     b.repository,
+		labelKeyJobName:        jobBase.JobDisplayName,
+		labelKeyJobWorkflowRef: jobBase.JobWorkflowRef,
+		labelKeyEventName:      jobBase.EventName,
+	}
+}
+
+func (b *baseLabels) scaleSetLabels() prometheus.Labels {
+	return prometheus.Labels{
+		labelKeyRunnerScaleSetName:      b.scaleSetName,
+		labelKeyRunnerScaleSetNamespace: b.scaleSetNamespace,
+		labelKeyEnterprise:              b.enterprise,
+		labelKeyOrganization:            b.organization,
+		labelKeyRepository:              b.repository,
+	}
+}
+
+func (b *baseLabels) completedJobLabels(msg *actions.JobCompleted) prometheus.Labels {
+	l := b.jobLabels(&msg.JobMessageBase)
+	l[labelKeyRunnerID] = strconv.Itoa(msg.RunnerId)
+	l[labelKeyJobResult] = msg.Result
+	l[labelKeyRunnerName] = msg.RunnerName
+	return l
+}
+
+func (b *baseLabels) startedJobLabels(msg *actions.JobStarted) prometheus.Labels {
+	l := b.jobLabels(&msg.JobMessageBase)
+	l[labelKeyRunnerID] = strconv.Itoa(msg.RunnerId)
+	l[labelKeyRunnerName] = msg.RunnerName
+	return l
+}
+
+//go:generate mockery --name Publisher --output ./mocks --outpkg mocks --case underscore
+type Publisher interface {
+	PublishStatic(min, max int)
+	PublishStatistics(stats *actions.RunnerScaleSetStatistic)
+	PublishJobStarted(msg *actions.JobStarted)
+	PublishJobCompleted(msg *actions.JobCompleted)
+	PublishDesiredRunners(count int)
+}
+
+//go:generate mockery --name ServerPublisher --output ./mocks --outpkg mocks --case underscore
+type ServerPublisher interface {
+	Publisher
+	ListenAndServe(ctx context.Context) error
+}
+
+var _ Publisher = &discard{}
+var _ ServerPublisher = &exporter{}
+
+var Discard Publisher = &discard{}
+
+type exporter struct {
+	logger logr.Logger
+	baseLabels
+	srv *http.Server
+}
+
+type ExporterConfig struct {
+	ScaleSetName      string
+	ScaleSetNamespace string
+	Enterprise        string
+	Organization      string
+	Repository        string
+	ServerAddr        string
+	ServerEndpoint    string
+	Logger            logr.Logger
+}
+
+func NewExporter(config ExporterConfig) ServerPublisher {
+	reg := prometheus.NewRegistry()
+	reg.MustRegister(
+		assignedJobs,
+		runningJobs,
+		registeredRunners,
+		busyRunners,
+		minRunners,
+		maxRunners,
+		desiredRunners,
+		idleRunners,
+		startedJobsTotal,
+		completedJobsTotal,
+		jobStartupDurationSeconds,
+		jobExecutionDurationSeconds,
+	)
+
+	mux := http.NewServeMux()
+	mux.Handle(
+		config.ServerEndpoint,
+		promhttp.HandlerFor(reg, promhttp.HandlerOpts{Registry: reg}),
+	)
+
+	return &exporter{
+		logger: config.Logger.WithName("metrics"),
+		baseLabels: baseLabels{
+			scaleSetName:      config.ScaleSetName,
+			scaleSetNamespace: config.ScaleSetNamespace,
+			enterprise:        config.Enterprise,
+			organization:      config.Organization,
+			repository:        config.Repository,
+		},
+		srv: &http.Server{
+			Addr:    config.ServerAddr,
+			Handler: mux,
+		},
+	}
+}
+
+func (e *exporter) ListenAndServe(ctx context.Context) error {
+	e.logger.Info("starting metrics server", "addr", e.srv.Addr)
+	go func() {
+		<-ctx.Done()
+		e.logger.Info("stopping metrics server")
+		e.srv.Shutdown(ctx)
+	}()
+	return e.srv.ListenAndServe()
+}
+
+func (m *exporter) PublishStatic(min, max int) {
+	l := m.scaleSetLabels()
+	maxRunners.With(l).Set(float64(max))
+	minRunners.With(l).Set(float64(min))
+}
+
+func (e *exporter) PublishStatistics(stats *actions.RunnerScaleSetStatistic) {
+	l := e.scaleSetLabels()
+
+	assignedJobs.With(l).Set(float64(stats.TotalAssignedJobs))
+	runningJobs.With(l).Set(float64(stats.TotalRunningJobs))
+	registeredRunners.With(l).Set(float64(stats.TotalRegisteredRunners))
+	busyRunners.With(l).Set(float64(stats.TotalBusyRunners))
+	idleRunners.With(l).Set(float64(stats.TotalIdleRunners))
+}
+
+func (e *exporter) PublishJobStarted(msg *actions.JobStarted) {
+	l := e.startedJobLabels(msg)
+	startedJobsTotal.With(l).Inc()
+
+	startupDuration := msg.JobMessageBase.RunnerAssignTime.Unix() - msg.JobMessageBase.ScaleSetAssignTime.Unix()
+	jobStartupDurationSeconds.With(l).Observe(float64(startupDuration))
+}
+
+func (e *exporter) PublishJobCompleted(msg *actions.JobCompleted) {
+	l := e.completedJobLabels(msg)
+	completedJobsTotal.With(l).Inc()
+
+	executionDuration := msg.JobMessageBase.FinishTime.Unix() - msg.JobMessageBase.RunnerAssignTime.Unix()
+	jobExecutionDurationSeconds.With(l).Observe(float64(executionDuration))
+}
+
+func (m *exporter) PublishDesiredRunners(count int) {
+	desiredRunners.With(m.scaleSetLabels()).Set(float64(count))
+}
+
+type discard struct{}
+
+func (*discard) PublishStatic(int, int)                             {}
+func (*discard) PublishStatistics(*actions.RunnerScaleSetStatistic) {}
+func (*discard) PublishJobStarted(*actions.JobStarted)              {}
+func (*discard) PublishJobCompleted(*actions.JobCompleted)          {}
+func (*discard) PublishDesiredRunners(int)                          {}

cmd/ghalistener/metrics/mocks/publisher.go

@@ -0,0 +1,53 @@
+// Code generated by mockery v2.36.1. DO NOT EDIT.
+
+package mocks
+
+import (
+	actions "github.com/actions/actions-runner-controller/github/actions"
+
+	mock "github.com/stretchr/testify/mock"
+)
+
+// Publisher is an autogenerated mock type for the Publisher type
+type Publisher struct {
+	mock.Mock
+}
+
+// PublishDesiredRunners provides a mock function with given fields: count
+func (_m *Publisher) PublishDesiredRunners(count int) {
+	_m.Called(count)
+}
+
+// PublishJobCompleted provides a mock function with given fields: msg
+func (_m *Publisher) PublishJobCompleted(msg *actions.JobCompleted) {
+	_m.Called(msg)
+}
+
+// PublishJobStarted provides a mock function with given fields: msg
+func (_m *Publisher) PublishJobStarted(msg *actions.JobStarted) {
+	_m.Called(msg)
+}
+
+// PublishStatic provides a mock function with given fields: min, max
+func (_m *Publisher) PublishStatic(min int, max int) {
+	_m.Called(min, max)
+}
+
+// PublishStatistics provides a mock function with given fields: stats
+func (_m *Publisher) PublishStatistics(stats *actions.RunnerScaleSetStatistic) {
+	_m.Called(stats)
+}
+
+// NewPublisher creates a new instance of Publisher. It also registers a testing interface on the mock and a cleanup function to assert the mocks expectations.
+// The first argument is typically a *testing.T value.
+func NewPublisher(t interface {
+	mock.TestingT
+	Cleanup(func())
+}) *Publisher {
+	mock := &Publisher{}
+	mock.Mock.Test(t)
+
+	t.Cleanup(func() { mock.AssertExpectations(t) })
+
+	return mock
+}

cmd/ghalistener/metrics/mocks/server_publisher.go

@@ -0,0 +1,69 @@
+// Code generated by mockery v2.36.1. DO NOT EDIT.
+
+package mocks
+
+import (
+	context "context"
+
+	actions "github.com/actions/actions-runner-controller/github/actions"
+
+	mock "github.com/stretchr/testify/mock"
+)
+
+// ServerPublisher is an autogenerated mock type for the ServerPublisher type
+type ServerPublisher struct {
+	mock.Mock
+}
+
+// ListenAndServe provides a mock function with given fields: ctx
+func (_m *ServerPublisher) ListenAndServe(ctx context.Context) error {
+	ret := _m.Called(ctx)
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(context.Context) error); ok {
+		r0 = rf(ctx)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
+// PublishDesiredRunners provides a mock function with given fields: count
+func (_m *ServerPublisher) PublishDesiredRunners(count int) {
+	_m.Called(count)
+}
+
+// PublishJobCompleted provides a mock function with given fields: msg
+func (_m *ServerPublisher) PublishJobCompleted(msg *actions.JobCompleted) {
+	_m.Called(msg)
+}
+
+// PublishJobStarted provides a mock function with given fields: msg
+func (_m *ServerPublisher) PublishJobStarted(msg *actions.JobStarted) {
+	_m.Called(msg)
+}
+
+// PublishStatic provides a mock function with given fields: min, max
+func (_m *ServerPublisher) PublishStatic(min int, max int) {
+	_m.Called(min, max)
+}
+
+// PublishStatistics provides a mock function with given fields: stats
+func (_m *ServerPublisher) PublishStatistics(stats *actions.RunnerScaleSetStatistic) {
+	_m.Called(stats)
+}
+
+// NewServerPublisher creates a new instance of ServerPublisher. It also registers a testing interface on the mock and a cleanup function to assert the mocks expectations.
+// The first argument is typically a *testing.T value.
+func NewServerPublisher(t interface {
+	mock.TestingT
+	Cleanup(func())
+}) *ServerPublisher {
+	mock := &ServerPublisher{}
+	mock.Mock.Test(t)
+
+	t.Cleanup(func() { mock.AssertExpectations(t) })
+
+	return mock
+}

cmd/ghalistener/worker/worker.go

@@ -0,0 +1,228 @@
+package worker
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"math"
+
+	"github.com/actions/actions-runner-controller/apis/actions.github.com/v1alpha1"
+	"github.com/actions/actions-runner-controller/cmd/ghalistener/listener"
+	"github.com/actions/actions-runner-controller/github/actions"
+	"github.com/actions/actions-runner-controller/logging"
+	jsonpatch "github.com/evanphx/json-patch"
+	"github.com/go-logr/logr"
+	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/rest"
+)
+
+const workerName = "kubernetesworker"
+
+type Option func(*Worker)
+
+func WithLogger(logger logr.Logger) Option {
+	return func(w *Worker) {
+		logger = logger.WithName(workerName)
+		w.logger = &logger
+	}
+}
+
+type Config struct {
+	EphemeralRunnerSetNamespace string
+	EphemeralRunnerSetName      string
+	MaxRunners                  int
+	MinRunners                  int
+}
+
+// The Worker's role is to process the messages it receives from the listener.
+// It then initiates Kubernetes API requests to carry out the necessary actions.
+type Worker struct {
+	clientset *kubernetes.Clientset
+	config    Config
+	lastPatch int
+	logger    *logr.Logger
+}
+
+var _ listener.Handler = (*Worker)(nil)
+
+func New(config Config, options ...Option) (*Worker, error) {
+	w := &Worker{
+		config:    config,
+		lastPatch: -1,
+	}
+
+	conf, err := rest.InClusterConfig()
+	if err != nil {
+		return nil, err
+	}
+
+	clientset, err := kubernetes.NewForConfig(conf)
+	if err != nil {
+		return nil, err
+	}
+
+	w.clientset = clientset
+
+	for _, option := range options {
+		option(w)
+	}
+
+	if err := w.applyDefaults(); err != nil {
+		return nil, err
+	}
+
+	return w, nil
+}
+
+func (w *Worker) applyDefaults() error {
+	if w.logger == nil {
+		logger, err := logging.NewLogger(logging.LogLevelDebug, logging.LogFormatJSON)
+		if err != nil {
+			return fmt.Errorf("NewLogger failed: %w", err)
+		}
+		logger = logger.WithName(workerName)
+		w.logger = &logger
+	}
+
+	return nil
+}
+
+// HandleJobStarted updates the job information for the ephemeral runner when a job is started.
+// It takes a context and a jobInfo parameter which contains the details of the started job.
+// This update marks the ephemeral runner so that the controller would have more context
+// about the ephemeral runner that should not be deleted when scaling down.
+// It returns an error if there is any issue with updating the job information.
+func (w *Worker) HandleJobStarted(ctx context.Context, jobInfo *actions.JobStarted) error {
+	w.logger.Info("Updating job info for the runner",
+		"runnerName", jobInfo.RunnerName,
+		"ownerName", jobInfo.OwnerName,
+		"repoName", jobInfo.RepositoryName,
+		"workflowRef", jobInfo.JobWorkflowRef,
+		"workflowRunId", jobInfo.WorkflowRunId,
+		"jobDisplayName", jobInfo.JobDisplayName,
+		"requestId", jobInfo.RunnerRequestId)
+
+	original, err := json.Marshal(&v1alpha1.EphemeralRunner{})
+	if err != nil {
+		return fmt.Errorf("failed to marshal empty ephemeral runner: %w", err)
+	}
+
+	patch, err := json.Marshal(
+		&v1alpha1.EphemeralRunner{
+			Status: v1alpha1.EphemeralRunnerStatus{
+				JobRequestId:      jobInfo.RunnerRequestId,
+				JobRepositoryName: fmt.Sprintf("%s/%s", jobInfo.OwnerName, jobInfo.RepositoryName),
+				WorkflowRunId:     jobInfo.WorkflowRunId,
+				JobWorkflowRef:    jobInfo.JobWorkflowRef,
+				JobDisplayName:    jobInfo.JobDisplayName,
+			},
+		},
+	)
+	if err != nil {
+		return fmt.Errorf("failed to marshal ephemeral runner patch: %w", err)
+	}
+
+	mergePatch, err := jsonpatch.CreateMergePatch(original, patch)
+	if err != nil {
+		return fmt.Errorf("failed to create merge patch json for ephemeral runner: %w", err)
+	}
+
+	w.logger.Info("Updating ephemeral runner with merge patch", "json", string(mergePatch))
+
+	patchedStatus := &v1alpha1.EphemeralRunner{}
+	err = w.clientset.RESTClient().
+		Patch(types.MergePatchType).
+		Prefix("apis", v1alpha1.GroupVersion.Group, v1alpha1.GroupVersion.Version).
+		Namespace(w.config.EphemeralRunnerSetNamespace).
+		Resource("EphemeralRunners").
+		Name(jobInfo.RunnerName).
+		SubResource("status").
+		Body(mergePatch).
+		Do(ctx).
+		Into(patchedStatus)
+	if err != nil {
+		return fmt.Errorf("could not patch ephemeral runner status, patch JSON: %s, error: %w", string(mergePatch), err)
+	}
+
+	w.logger.Info("Ephemeral runner status updated with the merge patch successfully.")
+
+	return nil
+}
+
+// HandleDesiredRunnerCount handles the desired runner count by scaling the ephemeral runner set.
+// The function calculates the target runner count based on the minimum and maximum runner count configuration.
+// If the target runner count is the same as the last patched count, it skips patching and returns nil.
+// Otherwise, it creates a merge patch JSON for updating the ephemeral runner set with the desired count.
+// The function then scales the ephemeral runner set by applying the merge patch.
+// Finally, it logs the scaled ephemeral runner set details and returns nil if successful.
+// If any error occurs during the process, it returns an error with a descriptive message.
+func (w *Worker) HandleDesiredRunnerCount(ctx context.Context, count int) error {
+	targetRunnerCount := int(math.Max(math.Min(float64(w.config.MaxRunners), float64(count)), float64(w.config.MinRunners)))
+
+	logValues := []any{
+		"assigned job", count,
+		"decision", targetRunnerCount,
+		"min", w.config.MinRunners,
+		"max", w.config.MaxRunners,
+		"currentRunnerCount", w.lastPatch,
+	}
+
+	if targetRunnerCount == w.lastPatch {
+		w.logger.Info("Skipping patching of EphemeralRunnerSet as the desired count has not changed", logValues...)
+		return nil
+	}
+
+	original, err := json.Marshal(
+		&v1alpha1.EphemeralRunnerSet{
+			Spec: v1alpha1.EphemeralRunnerSetSpec{
+				Replicas: -1,
+			},
+		},
+	)
+	if err != nil {
+		return fmt.Errorf("failed to marshal empty ephemeral runner set: %w", err)
+	}
+
+	patch, err := json.Marshal(
+		&v1alpha1.EphemeralRunnerSet{
+			Spec: v1alpha1.EphemeralRunnerSetSpec{
+				Replicas: count,
+			},
+		},
+	)
+	if err != nil {
+		w.logger.Error(err, "could not marshal patch ephemeral runner set")
+		return err
+	}
+
+	mergePatch, err := jsonpatch.CreateMergePatch(original, patch)
+	if err != nil {
+		return fmt.Errorf("failed to create merge patch json for ephemeral runner set: %w", err)
+	}
+
+	w.logger.Info("Created merge patch json for EphemeralRunnerSet update", "json", string(mergePatch))
+
+	w.logger.Info("Scaling ephemeral runner set", logValues...)
+
+	patchedEphemeralRunnerSet := &v1alpha1.EphemeralRunnerSet{}
+	err = w.clientset.RESTClient().
+		Patch(types.MergePatchType).
+		Prefix("apis", v1alpha1.GroupVersion.Group, v1alpha1.GroupVersion.Version).
+		Namespace(w.config.EphemeralRunnerSetNamespace).
+		Resource("ephemeralrunnersets").
+		Name(w.config.EphemeralRunnerSetName).
+		Body([]byte(mergePatch)).
+		Do(ctx).
+		Into(patchedEphemeralRunnerSet)
+	if err != nil {
+		return fmt.Errorf("could not patch ephemeral runner set , patch JSON: %s, error: %w", string(mergePatch), err)
+	}
+
+	w.logger.Info("Ephemeral runner set scaled.",
+		"namespace", w.config.EphemeralRunnerSetNamespace,
+		"name", w.config.EphemeralRunnerSetName,
+		"replicas", patchedEphemeralRunnerSet.Spec.Replicas,
+	)
+	return nil
+}

cmd/githubrunnerscalesetlistener/mock_KubernetesManager.go

@@ -1,4 +1,4 @@
-// Code generated by mockery v2.33.2. DO NOT EDIT.
+// Code generated by mockery v2.36.1. DO NOT EDIT.
 
 package main
 

cmd/githubrunnerscalesetlistener/mock_RunnerScaleSetClient.go

@@ -1,4 +1,4 @@
-// Code generated by mockery v2.33.2. DO NOT EDIT.
+// Code generated by mockery v2.36.1. DO NOT EDIT.
 
 package main
 

controllers/actions.github.com/resourcebuilder.go

@@ -38,8 +38,11 @@ var commonLabelKeys = [...]string{
 
 const labelValueKubernetesPartOf = "gha-runner-scale-set"
 
-var scaleSetListenerLogLevel = DefaultScaleSetListenerLogLevel
+var (
-var scaleSetListenerLogFormat = DefaultScaleSetListenerLogFormat
+	scaleSetListenerLogLevel   = DefaultScaleSetListenerLogLevel
+	scaleSetListenerLogFormat  = DefaultScaleSetListenerLogFormat
+	scaleSetListenerEntrypoint = "/ghalistener"
+)
 
 func SetListenerLoggingParameters(level string, format string) bool {
 	switch level {
@@ -59,6 +62,12 @@ func SetListenerLoggingParameters(level string, format string) bool {
 	return true
 }
 
+func SetListenerEntrypoint(entrypoint string) {
+	if entrypoint != "" {
+		scaleSetListenerEntrypoint = entrypoint
+	}
+}
+
 type resourceBuilder struct{}
 
 func (b *resourceBuilder) newAutoScalingListener(autoscalingRunnerSet *v1alpha1.AutoscalingRunnerSet, ephemeralRunnerSet *v1alpha1.EphemeralRunnerSet, namespace, image string, imagePullSecrets []corev1.LocalObjectReference) (*v1alpha1.AutoscalingListener, error) {
@@ -225,7 +234,7 @@ func (b *resourceBuilder) newScaleSetListenerPod(autoscalingListener *v1alpha1.A
 				Image: autoscalingListener.Spec.Image,
 				Env:   listenerEnv,
 				Command: []string{
-					"/github-runnerscaleset-listener",
+					scaleSetListenerEntrypoint,
 				},
 				Ports: ports,
 				VolumeMounts: []corev1.VolumeMount{

github/actions/mock_ActionsService.go

@@ -1,4 +1,4 @@
-// Code generated by mockery v2.33.2. DO NOT EDIT.
+// Code generated by mockery v2.36.1. DO NOT EDIT.
 
 package actions
 

github/actions/mock_SessionService.go

@@ -1,4 +1,4 @@
-// Code generated by mockery v2.33.2. DO NOT EDIT.
+// Code generated by mockery v2.36.1. DO NOT EDIT.
 
 package actions
 

main.go

@@ -203,6 +203,8 @@ func main() {
 		log.Info("Using default AutoscalingListener logging parameters", "LogLevel", actionsgithubcom.DefaultScaleSetListenerLogLevel, "LogFormat", actionsgithubcom.DefaultScaleSetListenerLogFormat)
 	}
 
+	actionsgithubcom.SetListenerEntrypoint(os.Getenv("LISTENER_ENTRYPOINT"))
+
 	var webhookServer webhook.Server
 	if port != 0 {
 		webhookServer = webhook.NewServer(webhook.Options{