service backend

api/fx/ingestor/internal/metrics/server.go

@@ -0,0 +1,134 @@
+package metrics
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"strings"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/tech/sendico/fx/ingestor/internal/config"
+	"github.com/tech/sendico/fx/ingestor/internal/fmerrors"
+	"github.com/tech/sendico/pkg/api/routers"
+	"github.com/tech/sendico/pkg/api/routers/health"
+	"github.com/tech/sendico/pkg/mlogger"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"go.uber.org/zap"
+)
+
+const (
+	defaultAddress        = ":9102"
+	readHeaderTimeout     = 5 * time.Second
+	defaultShutdownWindow = 5 * time.Second
+)
+
+type Server interface {
+	SetStatus(health.ServiceStatus)
+	Close(context.Context)
+}
+
+func NewServer(logger mlogger.Logger, cfg *config.MetricsConfig) (Server, error) {
+	if logger == nil {
+		return nil, fmerrors.New("metrics: logger is nil")
+	}
+	if cfg == nil || !cfg.Enabled {
+		logger.Debug("Metrics disabled; using noop server")
+		return noopServer{}, nil
+	}
+
+	address := strings.TrimSpace(cfg.Address)
+	if address == "" {
+		address = defaultAddress
+	}
+
+	metricsLogger := logger.Named("metrics")
+	router := chi.NewRouter()
+	router.Handle("/metrics", promhttp.Handler())
+
+	var healthRouter routers.Health
+	if hr, err := routers.NewHealthRouter(metricsLogger, router, ""); err != nil {
+		metricsLogger.Warn("Failed to initialise health router", zap.Error(err))
+	} else {
+		hr.SetStatus(health.SSStarting)
+		healthRouter = hr
+	}
+
+	httpServer := &http.Server{
+		Addr:              address,
+		Handler:           router,
+		ReadHeaderTimeout: readHeaderTimeout,
+	}
+
+	ms := &httpServerWrapper{
+		logger:  metricsLogger,
+		server:  httpServer,
+		health:  healthRouter,
+		timeout: defaultShutdownWindow,
+	}
+
+	go func() {
+		metricsLogger.Info("Prometheus endpoint listening", zap.String("address", address))
+		if err := httpServer.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
+			metricsLogger.Error("Prometheus endpoint stopped unexpectedly", zap.Error(err))
+			if healthRouter != nil {
+				healthRouter.SetStatus(health.SSTerminating)
+			}
+		}
+	}()
+
+	return ms, nil
+}
+
+type httpServerWrapper struct {
+	logger  mlogger.Logger
+	server  *http.Server
+	health  routers.Health
+	timeout time.Duration
+}
+
+func (s *httpServerWrapper) SetStatus(status health.ServiceStatus) {
+	if s == nil || s.health == nil {
+		return
+	}
+	s.logger.Debug("Updating metrics health status", zap.String("status", string(status)))
+	s.health.SetStatus(status)
+}
+
+func (s *httpServerWrapper) Close(ctx context.Context) {
+	if s == nil {
+		return
+	}
+
+	if s.health != nil {
+		s.health.SetStatus(health.SSTerminating)
+		s.health.Finish()
+		s.health = nil
+	}
+
+	if s.server == nil {
+		return
+	}
+
+	shutdownCtx := ctx
+	if shutdownCtx == nil {
+		shutdownCtx = context.Background()
+	}
+	if s.timeout > 0 {
+		var cancel context.CancelFunc
+		shutdownCtx, cancel = context.WithTimeout(shutdownCtx, s.timeout)
+		defer cancel()
+	}
+
+	if err := s.server.Shutdown(shutdownCtx); err != nil && !errors.Is(err, http.ErrServerClosed) {
+		s.logger.Warn("Failed to stop metrics server", zap.Error(err))
+	} else {
+		s.logger.Info("Metrics server stopped")
+	}
+}
+
+type noopServer struct{}
+
+func (noopServer) SetStatus(health.ServiceStatus) {}
+
+func (noopServer) Close(context.Context) {}