Load testing: synthetic VMs, multiple worker support and Grafana k6 test (#389)

* Load testing: synthetic VMs, multiple worker support and Grafana k6 test

* echoserver: prevent fallthrough when Accept() fails

* Move default local-dev context logic to CreateDevController()

* Synthetic: add a random delay to startup script echoing

internal/controller/api_workers.go

@@ -59,7 +59,7 @@ func (controller *Controller) createWorker(ctx *gin.Context) responder.Responder
 			return responder.Code(http.StatusInternalServerError)
 		}
 
-		if uint(len(workers)+1) > controller.maxWorkersPerLicense {
+		if !controller.synthetic && uint(len(workers)+1) > controller.maxWorkersPerLicense {
 			return responder.JSON(http.StatusConflict, NewErrorResponse("cannot register a new worker "+
 				"because the license capacity of %d workers has been reached, "+
 				"consider upgrading at https://tart.run/licensing/", controller.maxWorkersPerLicense))

internal/controller/controller.go

@@ -66,6 +66,7 @@ type Controller struct {
 	disableDBCompression bool
 	pingInterval         time.Duration
 	prometheusMetrics    bool
+	synthetic            bool
 
 	sshListenAddr   string
 	sshSigner       ssh.Signer

internal/controller/option.go

@@ -84,6 +84,12 @@ func WithPrometheusMetrics() Option {
 	}
 }
 
+func WithSynthetic() Option {
+	return func(controller *Controller) {
+		controller.synthetic = true
+	}
+}
+
 func WithLogger(logger *zap.Logger) Option {
 	return func(controller *Controller) {
 		controller.logger = logger.Sugar()