Silence limits as functions (#3885)

* Silence limits as functions

This commit changes silence limits from a struct of ints to a struct
of functions that return individual limits. This allows limits
to be lazy-loaded and updated without having to call silences.New().

Signed-off-by: George Robinson <george.robinson@grafana.com>

* Add explicit test for no limits

Signed-off-by: George Robinson <george.robinson@grafana.com>

* Fix run()

Signed-off-by: George Robinson <george.robinson@grafana.com>

---------

Signed-off-by: George Robinson <george.robinson@grafana.com>

cmd/alertmanager/main.go

@@ -262,8 +262,8 @@ func run() int {
 		SnapshotFile: filepath.Join(*dataDir, "silences"),
 		Retention:    *retention,
 		Limits: silence.Limits{
-			MaxSilences:        *maxSilences,
-			MaxPerSilenceBytes: *maxPerSilenceBytes,
+			MaxSilences:        func() int { return *maxSilences },
+			MaxPerSilenceBytes: func() int { return *maxPerSilenceBytes },
 		},
 		Logger:  log.With(logger, "component", "silences"),
 		Metrics: prometheus.DefaultRegisterer,

silence/silence.go

@@ -206,10 +206,10 @@ type Silences struct {
 type Limits struct {
 	// MaxSilences limits the maximum number of silences, including expired
 	// silences.
-	MaxSilences int
+	MaxSilences func() int
 	// MaxPerSilenceBytes is the maximum size of an individual silence as
 	// stored on disk.
-	MaxPerSilenceBytes int
+	MaxPerSilenceBytes func() int
 }
 
 // MaintenanceFunc represents the function to run as part of the periodic maintenance for silences.
@@ -585,8 +585,11 @@ func (s *Silences) setSilence(sil *pb.Silence, now time.Time, skipValidate bool)
 	// Check the limit unless the silence has been expired. This is to avoid
 	// situations where silences cannot be expired after the limit has been
 	// reduced.
-	if n := msil.Size(); s.limits.MaxPerSilenceBytes > 0 && n > s.limits.MaxPerSilenceBytes && sil.EndsAt.After(now) {
-		return fmt.Errorf("silence exceeded maximum size: %d bytes (limit: %d bytes)", n, s.limits.MaxPerSilenceBytes)
+	if s.limits.MaxPerSilenceBytes != nil {
+		n := msil.Size()
+		if m := s.limits.MaxPerSilenceBytes(); m > 0 && n > m && sil.EndsAt.After(now) {
+			return fmt.Errorf("silence exceeded maximum size: %d bytes (limit: %d bytes)", n, m)
+		}
 	}
 
 	if s.st.merge(msil, now) {
@@ -622,9 +625,9 @@ func (s *Silences) Set(sil *pb.Silence) (string, error) {
 	}
 
 	// If we got here it's either a new silence or a replacing one.
-	if s.limits.MaxSilences > 0 {
-		if len(s.st)+1 > s.limits.MaxSilences {
-			return "", fmt.Errorf("exceeded maximum number of silences: %d (limit: %d)", len(s.st), s.limits.MaxSilences)
+	if s.limits.MaxSilences != nil {
+		if m := s.limits.MaxSilences(); m > 0 && len(s.st)+1 > m {
+			return "", fmt.Errorf("exceeded maximum number of silences: %d (limit: %d)", len(s.st), m)
 		}
 	}
 

silence/silence_test.go

@@ -462,8 +462,8 @@ func TestSilenceSet(t *testing.T) {
 func TestSilenceLimits(t *testing.T) {
 	s, err := New(Options{
 		Limits: Limits{
-			MaxSilences:        1,
-			MaxPerSilenceBytes: 2 << 11, // 4KB
+			MaxSilences:        func() int { return 1 },
+			MaxPerSilenceBytes: func() int { return 2 << 11 }, // 4KB
 		},
 	})
 	require.NoError(t, err)
@@ -535,6 +535,24 @@ func TestSilenceLimits(t *testing.T) {
 	require.Equal(t, "", id3)
 }
 
+func TestSilenceNoLimits(t *testing.T) {
+	s, err := New(Options{
+		Limits: Limits{},
+	})
+	require.NoError(t, err)
+
+	// Insert sil should succeed without error.
+	sil := &pb.Silence{
+		Matchers: []*pb.Matcher{{Name: "a", Pattern: "b"}},
+		StartsAt: time.Now(),
+		EndsAt:   time.Now().Add(5 * time.Minute),
+		Comment:  strings.Repeat("c", 2<<9),
+	}
+	id, err := s.Set(sil)
+	require.NoError(t, err)
+	require.NotEqual(t, "", id)
+}
+
 func TestSetActiveSilence(t *testing.T) {
 	s, err := New(Options{
 		Retention: time.Hour,