[v2] Add IsReady method to App interface and implement connection checks

[ffelipelimao]

Description

This PR introduces a new IsReady() method to the Pitaya interface that provides one step to make a health check mechanism to determine if the metagame/connector is ready to serve requests.

Motivation

• Requests being routed to instances that haven't fully connected to required services (NATS, ETCD)
• Failed requests during service startup
• Difficulty implementing proper readiness probes in Kubernetes environments

Core Functionality

The IsReady() method validates:

• Application Running State: Checks if app.IsRunning() returns true
• NATS RPC Client Connection: Verifies NATS client is connected (if configured)
• NATS RPC Server Connection: Verifies NATS server is connected (if configured)
  -ETCD Service Discovery: Validates ETCD connection health (if configured)

Usage Example

HTTP Server to Health Check example

//main.go
func initializeServer(flags *cluster.StartCommandFlags) {
	var (
		viper       = viper.GetViper()
		logger      = logging.NewLogger(gameID, flags.ServerType, logFormat, verbosity)
		fieldLogger = logging.NewFieldLogger(gameID, flags.ServerType, logFormat, verbosity)
	)

	fixViperEnvVars(viper)

	err := configureJaeger(viper)
	if err != nil {
		logger.WithError(err).Error("Could not configure Jaeger")
	}

	if flags.ServerType == servers.CS {
		servers.StartCSServer(viper, logger, verbosity)
		return
	}

	var app pitaya.Pitaya

	switch flags.ServerType {
	case servers.Connector:
		app = servers.NewConnectorServer(viper, logger, flags)
	case servers.Metagame:
		app = servers.NewMetagameServer(viper, logger, fieldLogger, verbosity)
	case servers.WorkerClanWars:
		app = servers.NewWorkerClanWars(viper, logger)
	case servers.WorkerSplitServer:
		app = servers.NewWorkerSplitServer(viper, logger)
	default:
		logger.Fatalf("Unknown server type: %s", flags.ServerType)
	}

	pitaya.SetLogger(logger)
	
	// HERE
	go startHealthServer(app, 8080, logger)
	
	app.Start()  // Blocking Operation
}

//health_server.go
func startHealthServer(app pitaya.Pitaya, port int, logger interface{}) {
	http.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
		if app.IsRunning() {
			w.WriteHeader(http.StatusOK)
			fmt.Fprint(w, "alive")
		} else {
			w.WriteHeader(http.StatusServiceUnavailable)
			fmt.Fprint(w, "dead")
		}
	})

	http.HandleFunc("/readyz", func(w http.ResponseWriter, r *http.Request) {
		ctx, cancel := context.WithTimeout(r.Context(), 2*time.Second)
		defer cancel()
                 //HERE
		if app.IsReady(ctx) {
			w.WriteHeader(http.StatusOK)
			fmt.Fprint(w, "ready")
		} else {
			w.WriteHeader(http.StatusServiceUnavailable)
			fmt.Fprint(w, "not ready")
		}
	})

	http.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
		ctx, cancel := context.WithTimeout(r.Context(), 2*time.Second)
		defer cancel()

		ready := app.IsReady(ctx)
		status := map[string]interface{}{
			"ready":             ready,
			"running":           app.IsRunning(),
			"connected_clients": app.GetNumberOfConnectedClients(),
		}

		w.Header().Set("Content-Type", "application/json")
		if ready {
			w.WriteHeader(http.StatusOK)
		} else {
			w.WriteHeader(http.StatusServiceUnavailable)
		}
		json.NewEncoder(w).Encode(status)
	})

	if log, ok := logger.(interface{ Infof(string, ...interface{}) }); ok {
		log.Infof("Health check server listening on :%d", port)
	}

	if err := http.ListenAndServe(fmt.Sprintf(":%d", port), nil); err != nil {
		if log, ok := logger.(interface{ Errorf(string, ...interface{}) }); ok {
			log.Errorf("Health server error: %v", err)
		}
	}
}

[coveralls]

Pull Request Test Coverage Report for Build 20349108963

Details

• 0 of 42 (0.0%) changed or added relevant lines in 5 files are covered.
• 19 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.5%) to 61.46%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
cluster/nats_rpc_client.go	0	3	0.0%
cluster/nats_rpc_server.go	0	3	0.0%
static.go	0	3	0.0%
cluster/etcd_service_discovery.go	0	10	0.0%
app.go	0	23	0.0%

Files with Coverage Reduction	New Missed Lines	%
module.go	6	62.64%
app.go	13	66.78%

Totals
Change from base Build 19577298026:	-0.5%
Covered Lines:	5154
Relevant Lines:	8386

---

💛 - Coveralls

[rsafonseca]

LGTM :)