add metrics to embedr service

bskyweb/cmd/embedr/main.go

···
 					Value:    ":8100",
 					EnvVars:  []string{"HTTP_ADDRESS"},
 				},
+				&cli.StringFlag{
+					Name:     "metrics-address",
+					Usage:    "Specify the local IP/port to bind the metrics server to",
+					Required: false,
+					Value:    ":9090",
+					EnvVars:  []string{"METRICS_HTTP_ADDRESS"},
+				},
 				&cli.BoolFlag{
 					Name:     "debug",
 					Usage:    "Enable debug mode",

bskyweb/cmd/embedr/server.go

···
 	"github.com/bluesky-social/indigo/util/cliutil"
 	"github.com/bluesky-social/indigo/xrpc"
 	"github.com/bluesky-social/social-app/bskyweb"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 
-	"github.com/klauspost/compress/gzhttp"
-	"github.com/klauspost/compress/gzip"
+	"github.com/labstack/echo-contrib/echoprometheus"
 	"github.com/labstack/echo/v4"
 	"github.com/labstack/echo/v4/middleware"
+
+	"github.com/klauspost/compress/gzhttp"
+	"github.com/klauspost/compress/gzip"
 	"github.com/urfave/cli/v2"
 )
 
 type Server struct {
-	echo  *echo.Echo
-	httpd *http.Server
-	xrpcc *xrpc.Client
-	dir   identity.Directory
+	echo         *echo.Echo
+	httpd        *http.Server
+	metricsHttpd *http.Server
+	xrpcc        *xrpc.Client
+	dir          identity.Directory
 }
 
 func serve(cctx *cli.Context) error {
 	debug := cctx.Bool("debug")
 	httpAddress := cctx.String("http-address")
 	appviewHost := cctx.String("appview-host")
+	metricsAddress := cctx.String("metrics-address")
 
 	// Echo
 	e := echo.New()
···
 		return err
 	}
 
+	metricsMux := http.NewServeMux()
+	metricsMux.Handle("/metrics", promhttp.Handler())
+
+	metricsHttpd := &http.Server{
+		Addr:    metricsAddress,
+		Handler: metricsMux,
+	}
+
+	go func() {
+		if err := metricsHttpd.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
+			log.Error("failed to start metrics server", "error", err)
+		}
+	}()
+
 	//
 	// server
 	//
 	server := &Server{
-		echo:  e,
-		xrpcc: xrpcc,
-		dir:   identity.DefaultDirectory(),
+		echo:         e,
+		xrpcc:        xrpcc,
+		dir:          identity.DefaultDirectory(),
+		metricsHttpd: metricsHttpd,
 	}
 
 	// Create the HTTP server.
···
 	e.Use(middleware.RemoveTrailingSlashWithConfig(middleware.TrailingSlashConfig{
 		RedirectCode: http.StatusFound,
 	}))
+
+	e.Use(echoprometheus.NewMiddleware(""))
 
 	//
 	// configure routes
···
 
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()
+
+	// Shutdown metrics server too
+	if srv.metricsHttpd != nil {
+		srv.metricsHttpd.Shutdown(ctx)
+	}
 
 	return srv.httpd.Shutdown(ctx)
 }