fix(static/metrics/instance): fix duplicate metrics registration pani…

…c when recreating the instance (grafana#6608)

Signed-off-by: hainenber <dotronghai96@gmail.com>
(cherry picked from commit 7a61067)

CHANGELOG.md

@@ -17,6 +17,9 @@ internal API changes are not present.
 
 - Fix an issue where Loki could reject a batch of logs when structured metadata feature is used. (@thampiotr)
 
+- Fix a duplicate metrics registration panic when recreating static
+  mode metric instance's write handler. (@rfratto, @hainenber)
+
 v0.40.1 (2024-02-27)
 --------------------
 

pkg/metrics/instance/instance.go

@@ -409,7 +409,7 @@ func (i *Instance) initialize(ctx context.Context, reg prometheus.Registerer, cf
 		return fmt.Errorf("error creating WAL: %w", err)
 	}
 
-	i.writeHandler = remote.NewWriteHandler(i.logger, i.reg, i.wal)
+	i.writeHandler = remote.NewWriteHandler(i.logger, reg, i.wal)
 
 	i.discovery, err = i.newDiscoveryManager(ctx, cfg)
 	if err != nil {

pkg/metrics/instance/instance_test.go

@@ -258,7 +258,8 @@ func TestInstance_Recreate(t *testing.T) {
 	cfg.RemoteFlushDeadline = time.Hour
 
 	logger := log.NewLogfmtLogger(log.NewSyncWriter(os.Stderr))
-	inst, err := New(prometheus.NewRegistry(), cfg, walDir, logger)
+	currentReg := prometheus.NewRegistry()
+	inst, err := New(currentReg, cfg, walDir, logger)
 	require.NoError(t, err)
 
 	ctx, cancel := context.WithCancel(context.Background())
@@ -278,7 +279,7 @@ func TestInstance_Recreate(t *testing.T) {
 
 	// Recreate the instance, no panic should happen.
 	require.NotPanics(t, func() {
-		inst, err := New(prometheus.NewRegistry(), cfg, walDir, logger)
+		inst, err := New(currentReg, cfg, walDir, logger)
 		require.NoError(t, err)
 		runInstance(t, inst)