Use Patroni API to set bootstrap-only options. (#299)

Call Patroni API /config in order to set special options that are
ignored when set in the configuration file, such as max_connections.
Per https://github.com/zalando-incubator/postgres-operator/issues/297

* Some minor refacoring:

Rename Cluster ManualFailover to Swithover
Rename Patroni Failover to Switchover
Add more details to error messages and comments introduced in this PR.

Review by @zerg-junior

pkg/cluster/cluster.go

@@ -866,8 +866,8 @@ func (c *Cluster) GetStatus() *spec.ClusterStatus {
 	}
 }
 
-// ManualFailover does manual failover to a candidate pod
-func (c *Cluster) ManualFailover(curMaster *v1.Pod, candidate spec.NamespacedName) error {
+// Switchover does a switchover (via Patroni) to a candidate pod
+func (c *Cluster) Switchover(curMaster *v1.Pod, candidate spec.NamespacedName) error {
 	c.logger.Debugf("failing over from %q to %q", curMaster.Name, candidate)
 
 	podLabelErr := make(chan error)
@@ -889,7 +889,7 @@ func (c *Cluster) ManualFailover(curMaster *v1.Pod, candidate spec.NamespacedNam
 		}
 	}()
 
-	if err := c.patroni.Failover(curMaster, candidate.Name); err != nil {
+	if err := c.patroni.Switchover(curMaster, candidate.Name); err != nil {
 		close(stopCh)
 		return fmt.Errorf("could not failover: %v", err)
 	}

pkg/cluster/pod.go

@@ -232,7 +232,7 @@ func (c *Cluster) MigrateMasterPod(podName spec.NamespacedName) error {
 		}
 
 		masterCandidateName := util.NameFromMeta(pod.ObjectMeta)
-		if err := c.ManualFailover(oldMaster, masterCandidateName); err != nil {
+		if err := c.Switchover(oldMaster, masterCandidateName); err != nil {
 			return fmt.Errorf("could not failover to pod %q: %v", masterCandidateName, err)
 		}
 	} else {
@@ -330,7 +330,7 @@ func (c *Cluster) recreatePods() error {
 	if masterPod != nil {
 		// failover if we have not observed a master pod when re-creating former replicas.
 		if newMasterPod == nil && len(replicas) > 0 {
-			if err := c.ManualFailover(masterPod, masterCandidate(replicas)); err != nil {
+			if err := c.Switchover(masterPod, masterCandidate(replicas)); err != nil {
 				c.logger.Warningf("could not perform failover: %v", err)
 			}
 		} else if newMasterPod == nil && len(replicas) == 0 {

pkg/cluster/resources.go

@@ -125,7 +125,7 @@ func (c *Cluster) preScaleDown(newStatefulSet *v1beta1.StatefulSet) error {
 		return fmt.Errorf("pod %q does not belong to cluster", podName)
 	}
 
-	if err := c.patroni.Failover(&masterPod[0], masterCandidatePod.Name); err != nil {
+	if err := c.patroni.Switchover(&masterPod[0], masterCandidatePod.Name); err != nil {
 		return fmt.Errorf("could not failover: %v", err)
 	}
 

pkg/cluster/sync.go

@@ -229,6 +229,7 @@ func (c *Cluster) syncStatefulSet() error {
 	var (
 		podsRollingUpdateRequired bool
 	)
+	// NB: Be careful to consider the codepath that acts on podsRollingUpdateRequired before returning early.
 	sset, err := c.KubeClient.StatefulSets(c.Namespace).Get(c.statefulSetName(), metav1.GetOptions{})
 	if err != nil {
 		if !k8sutil.ResourceNotFound(err) {
@@ -288,6 +289,14 @@ func (c *Cluster) syncStatefulSet() error {
 			}
 		}
 	}
+
+	// Apply special PostgreSQL parameters that can only be set via the Patroni API.
+	// it is important to do it after the statefulset pods are there, but before the rolling update
+	// since those parameters require PostgreSQL restart.
+	if err := c.checkAndSetGlobalPostgreSQLConfiguration(); err != nil {
+		return fmt.Errorf("could not set cluster-wide PostgreSQL configuration options: %v", err)
+	}
+
 	// if we get here we also need to re-create the pods (either leftovers from the old
 	// statefulset or those that got their configuration from the outdated statefulset)
 	if podsRollingUpdateRequired {
@@ -303,6 +312,43 @@ func (c *Cluster) syncStatefulSet() error {
 	return nil
 }
 
+// checkAndSetGlobalPostgreSQLConfiguration checks whether cluster-wide API parameters
+// (like max_connections) has changed and if necessary sets it via the Patroni API
+func (c *Cluster) checkAndSetGlobalPostgreSQLConfiguration() error {
+	// we need to extract those options from the cluster manifest.
+	optionsToSet := make(map[string]string)
+	pgOptions := c.Spec.Parameters
+
+	for k, v := range pgOptions {
+		if isBootstrapOnlyParameter(k) {
+			optionsToSet[k] = v
+		}
+	}
+
+	if len(optionsToSet) > 0 {
+		pods, err := c.listPods()
+		if err != nil {
+			return err
+		}
+		if len(pods) == 0 {
+			return fmt.Errorf("could not call Patroni API: cluster has no pods")
+		}
+		for _, pod := range pods {
+			podName := util.NameFromMeta(pod.ObjectMeta)
+			c.logger.Debugf("calling Patroni API on a pod %s to set the following Postgres options: %v",
+				podName, optionsToSet)
+			if err := c.patroni.SetPostgresParameters(&pod, optionsToSet); err == nil {
+				return nil
+			} else {
+				c.logger.Warningf("could not patch postgres parameters with a pod %s: %v", podName, err)
+			}
+		}
+		return fmt.Errorf("could not reach Patroni API to set Postgres options: failed on every pod (%d total)",
+			len(pods))
+	}
+	return nil
+}
+
 func (c *Cluster) syncSecrets() error {
 	c.setProcessName("syncing secrets")
 	secrets := c.generateUserSecrets()

pkg/spec/types.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"log"
+	"os"
 	"strings"
 	"time"
 
@@ -14,6 +15,7 @@ import (
 	"k8s.io/client-go/pkg/apis/apps/v1beta1"
 	policyv1beta1 "k8s.io/client-go/pkg/apis/policy/v1beta1"
 	"k8s.io/client-go/rest"
+
 )
 
 // EventType contains type of the events for the TPRs and Pods received from Kubernetes
@@ -223,6 +225,9 @@ func (r RoleOrigin) String() string {
 // Placing this func here instead of pgk/util avoids circular import
 func GetOperatorNamespace() string {
 	if operatorNamespace == "" {
+		if namespaceFromEnvironment := os.Getenv("OPERATOR_NAMESPACE"); namespaceFromEnvironment != "" {
+			return namespaceFromEnvironment
+		}
 		operatorNamespaceBytes, err := ioutil.ReadFile(fileWithNamespace)
 		if err != nil {
 			log.Fatalf("Unable to detect operator namespace from within its pod due to: %v", err)

pkg/util/patroni/patroni.go

@@ -14,13 +14,15 @@ import (
 
 const (
 	failoverPath = "/failover"
+	configPath   = "/config"
 	apiPort      = 8008
 	timeout      = 30 * time.Second
 )
 
 // Interface describe patroni methods
 type Interface interface {
-	Failover(master *v1.Pod, candidate string) error
+	Switchover(master *v1.Pod, candidate string) error
+	SetPostgresParameters(server *v1.Pod, options map[string]string) error
 }
 
 // Patroni API client
@@ -45,20 +47,13 @@ func apiURL(masterPod *v1.Pod) string {
 	return fmt.Sprintf("http://%s:%d", masterPod.Status.PodIP, apiPort)
 }
 
-// Failover does manual failover via patroni api
-func (p *Patroni) Failover(master *v1.Pod, candidate string) error {
-	buf := &bytes.Buffer{}
-
-	err := json.NewEncoder(buf).Encode(map[string]string{"leader": master.Name, "member": candidate})
-	if err != nil {
-		return fmt.Errorf("could not encode json: %v", err)
-	}
-	request, err := http.NewRequest(http.MethodPost, apiURL(master)+failoverPath, buf)
+func (p *Patroni) httpPostOrPatch(method string, url string, body *bytes.Buffer) error {
+	request, err := http.NewRequest(method, url, body)
 	if err != nil {
 		return fmt.Errorf("could not create request: %v", err)
 	}
 
-	p.logger.Debugf("making http request: %s", request.URL.String())
+	p.logger.Debugf("making %s http request: %s", method, request.URL.String())
 
 	resp, err := p.httpClient.Do(request)
 	if err != nil {
@@ -74,6 +69,28 @@ func (p *Patroni) Failover(master *v1.Pod, candidate string) error {
 
 		return fmt.Errorf("patroni returned '%s'", string(bodyBytes))
 	}
+	return nil
+}
+
+// Switchover by calling Patroni REST API
+func (p *Patroni) Switchover(master *v1.Pod, candidate string) error {
+	buf := &bytes.Buffer{}
+	err := json.NewEncoder(buf).Encode(map[string]string{"leader": master.Name, "member": candidate})
+	if err != nil {
+		return fmt.Errorf("could not encode json: %v", err)
+	}
+	return p.httpPostOrPatch(http.MethodPost, apiURL(master)+failoverPath, buf)
 
 	return nil
 }
+
+//TODO: add an option call /patroni to check if it is necessary to restart the server
+// SetPostgresParameters sets Postgres options via Patroni patch API call.
+func (p *Patroni) SetPostgresParameters(server *v1.Pod, parameters map[string]string) error {
+	buf := &bytes.Buffer{}
+	err := json.NewEncoder(buf).Encode(map[string]map[string]interface{}{"postgresql": {"parameters": parameters}})
+	if err != nil {
+		return fmt.Errorf("could not encode json: %v", err)
+	}
+	return p.httpPostOrPatch(http.MethodPatch, apiURL(server)+configPath, buf)
+}