cortexproject · danielblando · Feb 26, 2025 · Feb 26, 2025 · yeya24 · Feb 26, 2025
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -5,6 +5,7 @@
 * [FEATURE] Query Frontend: Add dynamic interval size for query splitting. This is enabled by configuring experimental flags `querier.max-shards-per-query` and/or `querier.max-fetched-data-duration-per-query`. The split interval size is dynamically increased to maintain a number of shards and total duration fetched below the configured values. #6458
 * [FEATURE] Querier/Ruler: Add `query_partial_data` and `rules_partial_data` limits to allow queries/rules to be evaluated with data from a single zone, if other zones are not available. #6526
 * [FEATURE] Update prometheus alertmanager version to v0.28.0 and add new integration msteamsv2, jira, and rocketchat. #6590
+* [ENHANCEMENT] Alertmanager: Add new limits `-alertmanager.max-silences-count` and `-alertmanager.max-silences-size-bytes` for limiting silences per tenant. #6605
 * [ENHANCEMENT] Add `compactor.auto-forget-delay` for compactor to auto forget compactors after X minutes without heartbeat. #6533
 * [ENHANCEMENT] StoreGateway: Emit more histogram buckets on the `cortex_querier_storegateway_refetches_per_query` metric. #6570
 * [ENHANCEMENT] Querier: Apply bytes limiter to LabelNames and LabelValuesForLabelNames. #6568

diff --git a/docs/configuration/config-file-reference.md b/docs/configuration/config-file-reference.md
@@ -3751,6 +3751,15 @@ query_rejection:
 # CLI flag: -alertmanager.max-alerts-size-bytes
 [alertmanager_max_alerts_size_bytes: <int> | default = 0]
 
+# Maximum number of silences that a single user can have, including expired
+# silences. 0 = no limit.
+# CLI flag: -alertmanager.max-silences-count
+[alertmanager_max_silences_count: <int> | default = 0]
+
+# Maximum size of individual silences that a single user can have. 0 = no limit.
+# CLI flag: -alertmanager.max-silences-size-bytes
+[alertmanager_max_silences_size_bytes: <int> | default = 0]
+
 # list of rule groups to disable
 [disabled_rule_groups: <list of DisabledRuleGroup> | default = []]
 ```

diff --git a/pkg/alertmanager/alertmanager.go b/pkg/alertmanager/alertmanager.go
@@ -228,11 +228,16 @@ func New(cfg *Config, reg *prometheus.Registry) (*Alertmanager, error) {
 	am.groupMarker = memMarker
 
 	silencesFile := filepath.Join(cfg.TenantDataDir, silencesSnapshot)
+
 	am.silences, err = silence.New(silence.Options{
 		SnapshotFile: silencesFile,
 		Retention:    cfg.Retention,
-		Logger:       util_log.GoKitLogToSlog(log.With(am.logger, "component", "silences")),
-		Metrics:      am.registry,
+		Limits: silence.Limits{
+			MaxSilences:         func() int { return cfg.Limits.AlertmanagerMaxSilencesCount(cfg.UserID) },
+			MaxSilenceSizeBytes: func() int { return cfg.Limits.AlertmanagerMaxSilenceSizeBytes(cfg.UserID) },
+		},
+		Logger:  util_log.GoKitLogToSlog(log.With(am.logger, "component", "silences")),
+		Metrics: am.registry,
 	})
 	if err != nil {
 		return nil, fmt.Errorf("failed to create silences: %v", err)

diff --git a/pkg/alertmanager/alertmanager_test.go b/pkg/alertmanager/alertmanager_test.go
@@ -9,6 +9,7 @@ import (
 
 	"github.com/go-kit/log"
 	"github.com/prometheus/alertmanager/config"
+	"github.com/prometheus/alertmanager/silence/silencepb"
 	"github.com/prometheus/alertmanager/types"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/testutil"
@@ -19,6 +20,75 @@ import (
 	"github.com/cortexproject/cortex/pkg/util/test"
 )
 
+func TestSilencesLimits(t *testing.T) {
+	user := "test"
+
+	reg := prometheus.NewPedanticRegistry()
+	maxSilencesCount := 3
+	maxSilencesSizeBytes := 500
+	am, err := New(&Config{
+		UserID:          user,
+		Logger:          log.NewNopLogger(),
+		Limits:          &mockAlertManagerLimits{maxSilencesCount: maxSilencesCount, maxSilencesSizeBytes: maxSilencesSizeBytes},
+		TenantDataDir:   t.TempDir(),
+		ExternalURL:     &url.URL{Path: "/am"},
+		ShardingEnabled: false,
+		GCInterval:      30 * time.Minute,
+	}, reg)
+	require.NoError(t, err)
+	defer am.StopAndWait()
+
+	t.Run("Test maxSilencesCount", func(t *testing.T) {
+		createSilences := func() *silencepb.Silence {
+			return &silencepb.Silence{
+				Matchers: []*silencepb.Matcher{{Name: "name", Pattern: "pattern"}},
+				StartsAt: time.Now(),
+				EndsAt:   time.Now().Add(time.Minute * 30),
+			}
+		}
+
+		// create silences up to maxSilencesCount
+		for i := 0; i < maxSilencesCount; i++ {
+			err := am.silences.Set(createSilences())
+			require.NoError(t, err)
+		}
+
+		// exceeds limit
+		err = am.silences.Set(createSilences())
+		require.Error(t, err)
+		require.Equal(t, fmt.Sprintf("exceeded maximum number of silences: %d (limit: %d)", maxSilencesCount, maxSilencesCount), err.Error())
+
+		// expire whole silences
+		silences, _, err := am.silences.Query()
+		require.NoError(t, err)
+		for _, s := range silences {
+			err := am.silences.Expire(s.Id)
+			require.NoError(t, err)
+		}
+
+		// check maxSilencesCount includes expired silences
+		err = am.silences.Set(createSilences())
+		require.Error(t, err)
+		require.Equal(t, fmt.Sprintf("exceeded maximum number of silences: %d (limit: %d)", maxSilencesCount, maxSilencesCount), err.Error())
+
+		// GC
+		n, err := am.silences.GC()
+		require.NoError(t, err)
+		require.Equal(t, maxSilencesCount, n)
+	})
+	t.Run("Test maxSilencesSizeBytes", func(t *testing.T) {
+		bigSilences := &silencepb.Silence{
+			Matchers: []*silencepb.Matcher{{Name: strings.Repeat("a", maxSilencesSizeBytes/2+1), Pattern: strings.Repeat("b", maxSilencesSizeBytes/2+1)}},
+			StartsAt: time.Now(),
+			EndsAt:   time.Now().Add(time.Minute * 30),
+		}
+
+		err = am.silences.Set(bigSilences)
+		require.Error(t, err)
+		require.True(t, strings.Contains(err.Error(), "silence exceeded maximum size"))
+	})
+}
+
 func TestDispatcherGroupLimits(t *testing.T) {
 	for name, tc := range map[string]struct {
 		groups           int

diff --git a/pkg/alertmanager/multitenant.go b/pkg/alertmanager/multitenant.go
@@ -228,6 +228,12 @@ type Limits interface {
 	// AlertmanagerMaxAlertsSizeBytes returns total max size of alerts that tenant can have active at the same time. 0 = no limit.
 	// Size of the alert is computed from alert labels, annotations and generator URL.
 	AlertmanagerMaxAlertsSizeBytes(tenant string) int
+
+	// AlertmanagerMaxSilencesCount returns max number of silences that tenant can have, including expired silences. 0 = no limit.
+	AlertmanagerMaxSilencesCount(tenant string) int
+
+	// AlertmanagerMaxSilenceSizeBytes returns the maximum size of an individual silence. 0 = no limit.
+	AlertmanagerMaxSilenceSizeBytes(tenant string) int
 }
 
 // A MultitenantAlertmanager manages Alertmanager instances for multiple

diff --git a/pkg/alertmanager/multitenant_test.go b/pkg/alertmanager/multitenant_test.go
@@ -1777,8 +1777,14 @@ func TestAlertmanager_StateReplicationWithSharding(t *testing.T) {
 					amConfig.ShardingEnabled = true
 				}
 
+				var limits validation.Limits
+				flagext.DefaultValues(&limits)
+
+				overrides, err := validation.NewOverrides(limits, nil)
+				require.NoError(t, err)
+
 				reg := prometheus.NewPedanticRegistry()
-				am, err := createMultitenantAlertmanager(amConfig, nil, nil, mockStore, ringStore, nil, log.NewNopLogger(), reg)
+				am, err := createMultitenantAlertmanager(amConfig, nil, nil, mockStore, ringStore, overrides, log.NewNopLogger(), reg)
 				require.NoError(t, err)
 				defer services.StopAndAwaitTerminated(ctx, am) //nolint:errcheck
 
@@ -1969,8 +1975,14 @@ func TestAlertmanager_StateReplicationWithSharding_InitialSyncFromPeers(t *testi
 
 				amConfig.ShardingEnabled = true
 
+				var limits validation.Limits
+				flagext.DefaultValues(&limits)
+
+				overrides, err := validation.NewOverrides(limits, nil)
+				require.NoError(t, err)
+
 				reg := prometheus.NewPedanticRegistry()
-				am, err := createMultitenantAlertmanager(amConfig, nil, nil, mockStore, ringStore, nil, log.NewNopLogger(), reg)
+				am, err := createMultitenantAlertmanager(amConfig, nil, nil, mockStore, ringStore, overrides, log.NewNopLogger(), reg)
 				require.NoError(t, err)
 
 				clientPool.setServer(amConfig.ShardingRing.InstanceAddr+":0", am)
@@ -2285,6 +2297,8 @@ type mockAlertManagerLimits struct {
 	maxDispatcherAggregationGroups int
 	maxAlertsCount                 int
 	maxAlertsSizeBytes             int
+	maxSilencesCount               int
+	maxSilencesSizeBytes           int
 }
 
 func (m *mockAlertManagerLimits) AlertmanagerMaxConfigSize(tenant string) int {
@@ -2326,3 +2340,11 @@ func (m *mockAlertManagerLimits) AlertmanagerMaxAlertsCount(_ string) int {
 func (m *mockAlertManagerLimits) AlertmanagerMaxAlertsSizeBytes(_ string) int {
 	return m.maxAlertsSizeBytes
 }
+
+func (m *mockAlertManagerLimits) AlertmanagerMaxSilencesCount(_ string) int {
+	return m.maxSilencesCount
+}
+
+func (m *mockAlertManagerLimits) AlertmanagerMaxSilenceSizeBytes(_ string) int {
+	return m.maxSilencesSizeBytes
+}
diff --git a/pkg/util/validation/limits.go b/pkg/util/validation/limits.go
@@ -218,6 +218,8 @@ type Limits struct {
 	AlertmanagerMaxDispatcherAggregationGroups int                `yaml:"alertmanager_max_dispatcher_aggregation_groups" json:"alertmanager_max_dispatcher_aggregation_groups"`
 	AlertmanagerMaxAlertsCount                 int                `yaml:"alertmanager_max_alerts_count" json:"alertmanager_max_alerts_count"`
 	AlertmanagerMaxAlertsSizeBytes             int                `yaml:"alertmanager_max_alerts_size_bytes" json:"alertmanager_max_alerts_size_bytes"`
+	AlertmanagerMaxSilencesCount               int                `yaml:"alertmanager_max_silences_count" json:"alertmanager_max_silences_count"`
+	AlertmanagerMaxSilencesSizeBytes           int                `yaml:"alertmanager_max_silences_size_bytes" json:"alertmanager_max_silences_size_bytes"`
 	DisabledRuleGroups                         DisabledRuleGroups `yaml:"disabled_rule_groups" json:"disabled_rule_groups" doc:"nocli|description=list of rule groups to disable"`
 }
 
@@ -310,6 +312,8 @@ func (l *Limits) RegisterFlags(f *flag.FlagSet) {
 	f.IntVar(&l.AlertmanagerMaxDispatcherAggregationGroups, "alertmanager.max-dispatcher-aggregation-groups", 0, "Maximum number of aggregation groups in Alertmanager's dispatcher that a tenant can have. Each active aggregation group uses single goroutine. When the limit is reached, dispatcher will not dispatch alerts that belong to additional aggregation groups, but existing groups will keep working properly. 0 = no limit.")
 	f.IntVar(&l.AlertmanagerMaxAlertsCount, "alertmanager.max-alerts-count", 0, "Maximum number of alerts that a single user can have. Inserting more alerts will fail with a log message and metric increment. 0 = no limit.")
 	f.IntVar(&l.AlertmanagerMaxAlertsSizeBytes, "alertmanager.max-alerts-size-bytes", 0, "Maximum total size of alerts that a single user can have, alert size is the sum of the bytes of its labels, annotations and generatorURL. Inserting more alerts will fail with a log message and metric increment. 0 = no limit.")
+	f.IntVar(&l.AlertmanagerMaxSilencesCount, "alertmanager.max-silences-count", 0, "Maximum number of silences that a single user can have, including expired silences. 0 = no limit.")
+	f.IntVar(&l.AlertmanagerMaxSilencesSizeBytes, "alertmanager.max-silences-size-bytes", 0, "Maximum size of individual silences that a single user can have. 0 = no limit.")
 }
 
 // Validate the limits config and returns an error if the validation
@@ -971,6 +975,14 @@ func (o *Overrides) AlertmanagerMaxAlertsSizeBytes(userID string) int {
 	return o.GetOverridesForUser(userID).AlertmanagerMaxAlertsSizeBytes
 }
 
+func (o *Overrides) AlertmanagerMaxSilencesCount(userID string) int {
+	return o.GetOverridesForUser(userID).AlertmanagerMaxSilencesCount
+}
+
+func (o *Overrides) AlertmanagerMaxSilenceSizeBytes(userID string) int {
+	return o.GetOverridesForUser(userID).AlertmanagerMaxSilencesSizeBytes
+}
+
 func (o *Overrides) DisabledRuleGroups(userID string) DisabledRuleGroups {
 	if o.tenantLimits != nil {
 		l := o.tenantLimits.ByUserID(userID)