Run the guacgql HTTP server on only one port (#1805)

- Previously guacgql would run http.DefaultServeMux on
  two separate ports. One of them would conflict with
  the port used by Prometheus for guaccollect deps_dev.
  (The second port was used to provide Prometheus's
  /metrics route, but this was already present on the
  initial port, and it still is.)
- Fixes #1676

Signed-off-by: Narsimham Chelluri (Narsa) <narsa@kusari.dev>

cmd/guaccollect/cmd/deps_dev.go

@@ -84,7 +84,7 @@ you have access to read and write to the respective blob store.`,
 			viper.GetBool("retrieve-dependencies"),
 			args,
 			viper.GetBool("enable-prometheus"),
-			viper.GetInt("prometheus-addr"),
+			viper.GetInt("prometheus-port"),
 		)
 		if err != nil {
 			fmt.Printf("unable to validate flags: %v\n", err)
@@ -159,7 +159,7 @@ func validateDepsDevFlags(pubsubAddr string, blobAddr string, csubAddr string, c
 }
 
 func init() {
-	set, err := cli.BuildFlags([]string{"retrieve-dependencies"})
+	set, err := cli.BuildFlags([]string{"retrieve-dependencies", "prometheus-port"})
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "failed to setup flag: %v", err)
 		os.Exit(1)

cmd/guaccollect/cmd/root.go

@@ -29,7 +29,7 @@ import (
 func init() {
 	cobra.OnInitialize(cli.InitConfig)
 
-	set, err := cli.BuildFlags([]string{"pubsub-addr", "blob-addr", "csub-addr", "use-csub", "service-poll", "enable-prometheus", "prometheus-addr"})
+	set, err := cli.BuildFlags([]string{"pubsub-addr", "blob-addr", "csub-addr", "use-csub", "service-poll", "enable-prometheus"})
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "failed to setup flag: %v", err)
 		os.Exit(1)

cmd/guacgql/cmd/root.go

@@ -113,7 +113,7 @@ func init() {
 		"neptune-endpoint", "neptune-port", "neptune-region", "neptune-user", "neptune-realm",
 		"gql-listen-port", "gql-tls-cert-file", "gql-tls-key-file", "gql-debug", "gql-backend", "gql-trace",
 		"db-address", "db-driver", "db-debug", "db-migrate",
-		"kv-store", "kv-redis", "kv-tikv", "enable-prometheus", "prometheus-addr",
+		"kv-store", "kv-redis", "kv-tikv", "enable-prometheus",
 	})
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "failed to setup flag: %v", err)

pkg/cli/init.go

@@ -22,7 +22,6 @@ import (
 	"net/http"
 	"os"
 	"strings"
-	"time"
 
 	"github.com/guacsec/guac/pkg/logging"
 	"github.com/guacsec/guac/pkg/metrics"
@@ -71,39 +70,18 @@ func InitConfig() {
 	}
 }
 
-// SetupPrometheus sets up the prometheus server
+// SetupPrometheus sets up the Prometheus server, registering its handler on http.DefaultServeMux
 func SetupPrometheus(ctx context.Context, logger *zap.SugaredLogger, name string) (metrics.MetricCollector, error) {
-	if name == "" {
-		return nil, errors.New("name cannot be empty")
-	}
-	m := metrics.FromContext(ctx, name)
 	enablePrometheus := viper.GetBool("enable-prometheus")
-	prometheusPort := viper.GetInt("prometheus-addr")
 	if !enablePrometheus {
 		return nil, nil
 	}
 
-	go func() {
-		http.Handle("/metrics", m.MetricsHandler())
-		logger.Infof("Prometheus server is listening on: %d", prometheusPort)
-		server := &http.Server{Addr: fmt.Sprintf(":%d", prometheusPort)}
-
-		// Start server in a goroutine so that it doesn't block
-		go func() {
-			if err := server.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
-				logger.Fatalf("Error starting HTTP server: %v", err)
-			}
-		}()
-
-		// Listen for the cancellation signal
-		<-ctx.Done()
+	if name == "" {
+		return nil, errors.New("name cannot be empty")
+	}
 
-		// Shutdown the server when cancellation signal is received
-		shutdownCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
-		defer cancel()
-		if err := server.Shutdown(shutdownCtx); err != nil {
-			logger.Errorf("Error shutting down server: %v", err)
-		}
-	}()
+	m := metrics.FromContext(ctx, name)
+	http.Handle("/metrics", m.MetricsHandler())
 	return m, nil
 }

pkg/cli/store.go

@@ -91,7 +91,7 @@ func init() {
 
 	set.Bool("enable-prometheus", true, "enable prometheus metrics")
 
-	set.Int("prometheus-addr", 9091, "port to listen to on prometheus server")
+	set.Int("prometheus-port", 9091, "port to listen to on prometheus server")
 
 	set.StringP("interval", "i", "5m", "if polling set interval, m, h, s, etc.")
 

pkg/metrics/README.md

@@ -21,7 +21,7 @@ To use this metrics package in your application, you need to do the following:
 To scrape the metrics from Prometheus, you can use the following example:
 
 ```bash
-curl http://localhost:9091/metrics
+curl http://localhost:8080/metrics
 ```
 
 This will return a plain text page with a series of lines like this: