✨ Integrate monitoring server for observability, adding health and metrics endpoints. Update configuration to enable monitoring features and enhance README with deployment examples for Kubernetes and systemd. Refactor application initialization to include monitoring server setup and improve error handling in message processing metrics.

internal/infra/monitoring/server.go

@@ -0,0 +1,144 @@
+package monitoring
+
+import (
+	"caatsm/internal/infra/config"
+	obsmetrics "caatsm/internal/observability/metrics"
+	"context"
+	"encoding/json"
+	"errors"
+	"net/http"
+	"time"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+	"github.com/nats-io/nats.go"
+	"go.uber.org/zap"
+)
+
+// Server exposes /healthz and /metrics endpoints for basic operations and observability checks.
+type Server struct {
+	cfg        config.MonitoringConfig
+	logger     *zap.Logger
+	pool       *pgxpool.Pool
+	conn       *nats.Conn
+	httpServer *http.Server
+}
+
+// ProvideServer wires a monitoring server if enabled in configuration.
+func ProvideServer(
+	cfg *config.Config,
+	logger *zap.Logger,
+	pool *pgxpool.Pool,
+	conn *nats.Conn,
+) (*Server, error) {
+	if cfg == nil || logger == nil || cfg.Monitoring.Disabled {
+		return nil, nil
+	}
+	if cfg.Monitoring.Addr == "" {
+		return nil, nil
+	}
+
+	mux := http.NewServeMux()
+	server := &Server{
+		cfg:    cfg.Monitoring,
+		logger: logger,
+		pool:   pool,
+		conn:   conn,
+	}
+
+	routes := 0
+	if cfg.Monitoring.EnableHealth {
+		mux.HandleFunc("/healthz", server.handleHealth)
+		routes++
+	}
+	if cfg.Monitoring.EnableMetrics {
+		mux.Handle("/metrics", obsmetrics.Handler())
+		routes++
+	}
+
+	if routes == 0 {
+		return nil, nil
+	}
+
+	httpServer := &http.Server{
+		Addr:              cfg.Monitoring.Addr,
+		Handler:           mux,
+		ReadHeaderTimeout: 3 * time.Second,
+		ReadTimeout:       cfg.Monitoring.ReadTimeout,
+		WriteTimeout:      cfg.Monitoring.WriteTimeout,
+	}
+	server.httpServer = httpServer
+
+	return server, nil
+}
+
+// Start launches the monitoring HTTP server in the background.
+func (s *Server) Start(ctx context.Context) error {
+	if s == nil || s.httpServer == nil {
+		return nil
+	}
+
+	go func() {
+		<-ctx.Done()
+		_ = s.Shutdown(context.Background())
+	}()
+
+	go func() {
+		s.logger.Info("Monitoring server listening",
+			zap.String("addr", s.httpServer.Addr),
+			zap.Bool("metrics", s.cfg.EnableMetrics),
+			zap.Bool("health", s.cfg.EnableHealth),
+		)
+		if err := s.httpServer.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
+			s.logger.Error("Monitoring server exited", zap.Error(err))
+		}
+	}()
+
+	return nil
+}
+
+// Shutdown gracefully stops the HTTP server.
+func (s *Server) Shutdown(ctx context.Context) error {
+	if s == nil || s.httpServer == nil {
+		return nil
+	}
+	return s.httpServer.Shutdown(ctx)
+}
+
+func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
+	status := http.StatusOK
+	result := map[string]interface{}{
+		"postgres": "ok",
+		"nats":     "ok",
+	}
+
+	ctx, cancel := context.WithTimeout(r.Context(), s.healthTimeout())
+	defer cancel()
+
+	if s.pool == nil {
+		result["postgres"] = "unconfigured"
+		status = http.StatusServiceUnavailable
+	} else if err := s.pool.Ping(ctx); err != nil {
+		result["postgres"] = err.Error()
+		status = http.StatusServiceUnavailable
+	}
+
+	if s.conn == nil {
+		result["nats"] = "unconfigured"
+		status = http.StatusServiceUnavailable
+	} else if s.conn.Status() != nats.CONNECTED {
+		result["nats"] = s.conn.Status().String()
+		status = http.StatusServiceUnavailable
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(result)
+}
+
+func (s *Server) healthTimeout() time.Duration {
+	timeout := s.cfg.HealthTimeout
+	if timeout <= 0 {
+		timeout = 2 * time.Second
+	}
+	return timeout
+}