fix: alertmanager user config disappearing when ring is unreachable

CHANGELOG.md

@@ -4,6 +4,7 @@
 * [ENHANCEMENT] Cache: Add per-tenant TTL configuration for query results cache to control cache expiration on a per-tenant basis with separate TTLs for regular and out-of-order data. #7357
 * [ENHANCEMENT] Tenant Federation: Add a local cache to regex resolver. #7363
 * [ENHANCEMENT] Query Scheduler: Add `cortex_query_scheduler_tracked_requests` metric to track the current number of requests held by the scheduler. #7355
+* [BUGFIX] Alertmanager: Fix disappearing user config and state when ring is temporarily unreachable. #7372
 * [BUGFIX] Fix nil when ingester_query_max_attempts > 1. #7369
 
 ## 1.21.0 in progress

pkg/alertmanager/multitenant.go

@@ -714,7 +714,10 @@ func (am *MultitenantAlertmanager) userIndexUpdateLoop(ctx context.Context) {
 			level.Error(am.logger).Log("msg", "context timeout, exit user index update loop", "err", ctx.Err())
 			return
 		case <-ticker.C:
-			owned := am.isUserOwned(userID)
+			owned, err := am.isUserOwned(userID)
+			if err != nil {
+				continue
+			}
 			if !owned {
 				continue
 			}
@@ -804,7 +807,11 @@ func (am *MultitenantAlertmanager) loadAlertmanagerConfigs(ctx context.Context)
 
 	// Filter out users not owned by this shard.
 	for _, userID := range allUserIDs {
-		if am.isUserOwned(userID) {
+		owned, err := am.isUserOwned(userID)
+		if err != nil {
+			return nil, nil, errors.Wrapf(err, "failed to check if user %s is owned", userID)
+		}
+		if owned {
 			ownedUserIDs = append(ownedUserIDs, userID)
 		}
 	}
@@ -821,24 +828,24 @@ func (am *MultitenantAlertmanager) loadAlertmanagerConfigs(ctx context.Context)
 	return allUserIDs, configs, nil
 }
 
-func (am *MultitenantAlertmanager) isUserOwned(userID string) bool {
+func (am *MultitenantAlertmanager) isUserOwned(userID string) (bool, error) {
 	if !am.allowedTenants.IsAllowed(userID) {
-		return false
+		return false, nil
 	}
 
 	// If sharding is disabled, any alertmanager instance owns all users.
 	if !am.cfg.ShardingEnabled {
-		return true
+		return true, nil
 	}
 
 	alertmanagers, err := am.ring.Get(users.ShardByUser(userID), getSyncRingOp(am.cfg.ShardingRing.DisableReplicaSetExtension), nil, nil, nil)
 	if err != nil {
 		am.ringCheckErrors.Inc()
 		level.Error(am.logger).Log("msg", "failed to load alertmanager configuration", "user", userID, "err", err)
-		return false
+		return false, err
 	}
 
-	return alertmanagers.Includes(am.ringLifecycler.GetInstanceAddr())
+	return alertmanagers.Includes(am.ringLifecycler.GetInstanceAddr()), nil
 }
 
 func (am *MultitenantAlertmanager) syncConfigs(cfgs map[string]alertspb.AlertConfigDesc) {

pkg/alertmanager/multitenant_test.go

@@ -2501,3 +2501,128 @@ func (m *mockAlertManagerLimits) AlertmanagerMaxSilencesCount(_ string) int {
 func (m *mockAlertManagerLimits) AlertmanagerMaxSilenceSizeBytes(_ string) int {
 	return m.maxSilencesSizeBytes
 }
+
+func TestMultitenantAlertmanager_isUserOwned(t *testing.T) {
+	ctx := context.Background()
+	_ = ctx
+	amConfig := mockAlertmanagerConfig(t)
+	amConfig.ShardingEnabled = true
+
+	ringStore, closer := consul.NewInMemoryClient(ring.GetCodec(), log.NewNopLogger(), nil)
+	t.Cleanup(func() { assert.NoError(t, closer.Close()) })
+
+	alertStore, err := prepareInMemoryAlertStore()
+	require.NoError(t, err)
+
+	am, err := createMultitenantAlertmanager(amConfig, nil, nil, alertStore, ringStore, nil, log.NewNopLogger(), nil)
+	require.NoError(t, err)
+
+	// We don't start the AM, so the ring is empty.
+	// When sharding is enabled, isUserOwned will call am.ring.Get, which should fail because the ring is empty.
+	owned, err := am.isUserOwned("user-1")
+	require.Error(t, err)
+	require.Equal(t, ring.ErrEmptyRing, err)
+	require.False(t, owned)
+
+	// If sharding is disabled, it should return true, nil
+	am.cfg.ShardingEnabled = false
+	owned, err = am.isUserOwned("user-1")
+	require.NoError(t, err)
+	require.True(t, owned)
+}
+
+func TestMultitenantAlertmanager_loadAndSyncConfigs_deletesUserFromStore(t *testing.T) {
+	ctx := context.Background()
+	amConfig := mockAlertmanagerConfig(t)
+	amConfig.ShardingEnabled = true
+
+	ringStore, closer := consul.NewInMemoryClient(ring.GetCodec(), log.NewNopLogger(), nil)
+	t.Cleanup(func() { assert.NoError(t, closer.Close()) })
+
+	alertStore, err := prepareInMemoryAlertStore()
+	require.NoError(t, err)
+
+	am, err := createMultitenantAlertmanager(amConfig, nil, nil, alertStore, ringStore, nil, log.NewNopLogger(), nil)
+	require.NoError(t, err)
+
+	// We don't start the AM. We just manually insert state, then call loadAndSyncConfigs.
+	user1 := "user-1"
+
+	// 1. Create a FullState (remote state) for user1 in the store.
+	fullState := alertspb.FullStateDesc{
+		State: &clusterpb.FullState{},
+	}
+	err = alertStore.SetFullState(ctx, user1, fullState)
+	require.NoError(t, err)
+
+	// Since we did NOT SetAlertConfig for user1, the store.ListAllUsers will return empty.
+	allUsers, err := alertStore.ListAllUsers(ctx)
+	require.NoError(t, err)
+	require.Empty(t, allUsers)
+
+	// Verify user1's FullState is written to the store.
+	_, err = alertStore.GetFullState(ctx, user1)
+	require.NoError(t, err)
+
+	// 2. Call loadAndSyncConfigs. It should fetch all users (which is empty),
+	// and since sharding is enabled, it should clean up unused remote state for any users not in the list.
+	// user1 has state but no config, so its state should be pruned.
+	err = am.loadAndSyncConfigs(ctx, reasonPeriodic)
+	require.NoError(t, err)
+
+	// 3. Verify user1's FullState is deleted from the store.
+	_, err = alertStore.GetFullState(ctx, user1)
+	require.Error(t, err)
+	require.Equal(t, alertspb.ErrNotFound, err)
+}
+
+func TestMultitenantAlertmanager_loadAndSyncConfigs_DoesNotDeleteUserFromStoreWhenRingUnreachable(t *testing.T) {
+	ctx := context.Background()
+	amConfig := mockAlertmanagerConfig(t)
+	amConfig.ShardingEnabled = true
+
+	ringStore, closer := consul.NewInMemoryClient(ring.GetCodec(), log.NewNopLogger(), nil)
+	t.Cleanup(func() { assert.NoError(t, closer.Close()) })
+
+	alertStore, err := prepareInMemoryAlertStore()
+	require.NoError(t, err)
+
+	am, err := createMultitenantAlertmanager(amConfig, nil, nil, alertStore, ringStore, nil, log.NewNopLogger(), nil)
+	require.NoError(t, err)
+
+	user1 := "user-1"
+
+	// 1. Create a FullState (remote state) for user1 in the store.
+	fullState := alertspb.FullStateDesc{
+		State: &clusterpb.FullState{},
+	}
+	err = alertStore.SetFullState(ctx, user1, fullState)
+	require.NoError(t, err)
+
+	// Since we DO SetAlertConfig for user1, the store.ListAllUsers will return the user.
+	err = alertStore.SetAlertConfig(ctx, alertspb.AlertConfigDesc{
+		User:      user1,
+		RawConfig: simpleConfigOne,
+		Templates: []*alertspb.TemplateDesc{},
+	})
+	require.NoError(t, err)
+
+	allUsers, err := alertStore.ListAllUsers(ctx)
+	require.NoError(t, err)
+	require.Len(t, allUsers, 1)
+
+	// Verify user1's FullState is written to the store.
+	_, err = alertStore.GetFullState(ctx, user1)
+	require.NoError(t, err)
+
+	// 2. Call loadAndSyncConfigs. It should fetch all users.
+	// Since sharding is enabled but ring is empty (unreachable), isUserOwned will fail.
+	// loadAndSyncConfigs will return early with an error before pruning any states!
+	err = am.loadAndSyncConfigs(ctx, reasonPeriodic)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), ring.ErrEmptyRing.Error())
+
+	// 3. Verify user1's FullState is STILL in the store.
+	_, err = alertStore.GetFullState(ctx, user1)
+	require.NoError(t, err)
+}