fixed registry bug with debug config (#722)

cmd/hauler/cli/store/serve.go

@@ -126,6 +126,18 @@ func ServeRegistryCmd(ctx context.Context, o *flags.ServeRegistryOpts, s *store.
 		return err
 	}
 
+	if cfg.HTTP.Debug.Addr != "" {
+		l.Infof("starting debug server on address [%s]", cfg.HTTP.Debug.Addr)
+		if cfg.HTTP.Debug.Prometheus.Enabled {
+			path := cfg.HTTP.Debug.Prometheus.Path
+			if path == "" {
+				path = "/metrics"
+			}
+			l.Infof("providing prometheus metrics on [%s]", path)
+		}
+	}
+	server.ConfigureDebugServer(cfg)
+
 	if err = r.ListenAndServe(); err != nil {
 		return err
 	}

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/containerd/errdefs v1.0.0
 	github.com/distribution/distribution/v3 v3.1.1
 	github.com/distribution/reference v0.6.0
+	github.com/docker/go-metrics v0.0.1
 	github.com/dustin/go-humanize v1.0.1
 	github.com/google/go-containerregistry v0.21.9
 	github.com/google/uuid v1.6.0
@@ -132,7 +133,6 @@ require (
 	github.com/docker/docker-credential-helpers v0.9.5 // indirect
 	github.com/docker/go-connections v0.7.0 // indirect
 	github.com/docker/go-events v0.0.0-20250808211157-605354379745 // indirect
-	github.com/docker/go-metrics v0.0.1 // indirect
 	github.com/docker/go-units v0.5.0 // indirect
 	github.com/dsnet/compress v0.0.2-0.20230904184137-39efe44ab707 // indirect
 	github.com/dylibso/observe-sdk/go v0.0.0-20240819160327-2d926c5d788a // indirect

internal/server/registry.go

@@ -11,6 +11,7 @@ import (
 	"github.com/distribution/distribution/v3/configuration"
 	"github.com/distribution/distribution/v3/registry"
 	"github.com/distribution/distribution/v3/registry/handlers"
+	dockermetrics "github.com/docker/go-metrics"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 )
@@ -24,6 +25,27 @@ func NewRegistry(ctx context.Context, cfg *configuration.Configuration) (*regist
 	return r, nil
 }
 
+// ConfigureDebugServer starts pprof/expvar/prometheus on cfg.HTTP.Debug.Addr
+func ConfigureDebugServer(cfg *configuration.Configuration) {
+	if cfg.HTTP.Debug.Addr == "" {
+		return
+	}
+
+	if cfg.HTTP.Debug.Prometheus.Enabled {
+		path := cfg.HTTP.Debug.Prometheus.Path
+		if path == "" {
+			path = "/metrics"
+		}
+		http.Handle(path, dockermetrics.Handler())
+	}
+
+	go func(addr string) {
+		if err := http.ListenAndServe(addr, nil); err != nil { //nolint:gosec // debug interface: internal-only, no read/write timeouts needed
+			logrus.Fatalf("error listening on debug interface: %v", err)
+		}
+	}(cfg.HTTP.Debug.Addr)
+}
+
 type tmpRegistryServer struct {
 	*httptest.Server
 }

internal/server/server_test.go

@@ -2,10 +2,14 @@ package server
 
 import (
 	"context"
+	"io"
+	"net"
 	"net/http"
 	"strings"
 	"testing"
+	"time"
 
+	"github.com/distribution/distribution/v3/configuration"
 	// Register the filesystem storage driver for the distribution registry.
 	_ "github.com/distribution/distribution/v3/registry/storage/driver/filesystem"
 
@@ -16,9 +20,8 @@ func TestNewTempRegistry_StartStop(t *testing.T) {
 	ctx := context.Background()
 	srv := NewTempRegistry(ctx, t.TempDir())
 
-	// Start the httptest server directly to avoid the Start() method's
-	// retry logic which only accepts HTTP 200, while /v2 returns 401
-	// from the distribution registry.
+	// start the httptest server directly to avoid the retry logic which only accepts HTTP 200
+	// while /v2 returns 401 from the distribution registry.
 	srv.Server.Start()
 	t.Cleanup(func() { srv.Stop() })
 
@@ -74,6 +77,55 @@ func TestNewFile_Configuration(t *testing.T) {
 	}
 }
 
+// this is the only test in the package allowed to enable prometheus, since it registers
+// on http.DefaultServeMux and a second registration would panic.
+func TestConfigureDebugServer_Prometheus(t *testing.T) {
+	// grab a free port and release it so ConfigureDebugServer can bind it
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("failed to reserve a free port: %v", err)
+	}
+	addr := l.Addr().String()
+	l.Close()
+
+	cfg := &configuration.Configuration{}
+	cfg.HTTP.Debug.Addr = addr
+	cfg.HTTP.Debug.Prometheus.Enabled = true
+	cfg.HTTP.Debug.Prometheus.Path = "/metrics"
+
+	ConfigureDebugServer(cfg)
+
+	var resp *http.Response
+	for i := 0; i < 20; i++ {
+		resp, err = http.Get("http://" + addr + "/metrics")
+		if err == nil {
+			break
+		}
+		time.Sleep(50 * time.Millisecond)
+	}
+	if err != nil {
+		t.Fatalf("expected GET /metrics to eventually succeed, got error: %v", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("expected status 200 from the prometheus handler, got %d", resp.StatusCode)
+	}
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		t.Fatalf("failed to read response body: %v", err)
+	}
+	if !strings.Contains(string(body), "go_gc_duration_seconds") {
+		t.Fatalf("expected prometheus-formatted metrics output, got: %s", body)
+	}
+}
+
+// an empty Debug.Addr should just no-op, not start a listener.
+func TestConfigureDebugServer_NoAddr(t *testing.T) {
+	ConfigureDebugServer(&configuration.Configuration{})
+}
+
 func TestNewFile_DefaultPort(t *testing.T) {
 	ctx := context.Background()
 	opts := flags.ServeFilesOpts{