Fix panics in DurationWithJitter utils when computed variance is zero.

CHANGELOG.md

@@ -50,6 +50,7 @@
 * [BUGFIX] Query-frontend: Add flag `-query-frontend.prom2-range-compat` and corresponding YAML to rewrite queries with ranges that worked in Prometheus 2 but are invalid in Prometheus 3. #10445 #10461 #10502
 * [BUGFIX] Distributor: Fix edge case at the HA-tracker with memberlist as KVStore, where when a replica in the KVStore is marked as deleted but not yet removed, it fails to update the KVStore. #10443
 * [BUGFIX] Ingester: Fixed a race condition in the `PostingsForMatchers` cache that may have infrequently returned expired cached postings. #10500
+* [BUGFIX] Fix panics in `DurationWithJitter` util functions when computed variance is zero. #10507
 
 ### Mixin
 

pkg/util/time.go

@@ -72,6 +72,10 @@ func DurationWithJitter(input time.Duration, variancePerc float64) time.Duration
 	}
 
 	variance := int64(float64(input) * variancePerc)
+	if variance == 0 {
+		return 0
+	}
+
 	jitter := rand.Int63n(variance*2) - variance
 
 	return input + time.Duration(jitter)
@@ -85,6 +89,10 @@ func DurationWithPositiveJitter(input time.Duration, variancePerc float64) time.
 	}
 
 	variance := int64(float64(input) * variancePerc)
+	if variance == 0 {
+		return 0
+	}
+
 	jitter := rand.Int63n(variance)
 
 	return input + time.Duration(jitter)
@@ -98,6 +106,10 @@ func DurationWithNegativeJitter(input time.Duration, variancePerc float64) time.
 	}
 
 	variance := int64(float64(input) * variancePerc)
+	if variance == 0 {
+		return 0
+	}
+
 	jitter := rand.Int63n(variance)
 
 	return input - time.Duration(jitter)

pkg/util/time_test.go

@@ -72,6 +72,10 @@ func TestDurationWithJitter_ZeroInputDuration(t *testing.T) {
 	assert.Equal(t, time.Duration(0), DurationWithJitter(time.Duration(0), 0.5))
 }
 
+func TestDurationWithJitter_SmallInput(t *testing.T) {
+	assert.Equal(t, time.Duration(0), DurationWithJitter(time.Duration(7), 0.1))
+}
+
 func TestDurationWithPositiveJitter(t *testing.T) {
 	const numRuns = 1000
 
@@ -86,6 +90,10 @@ func TestDurationWithPositiveJitter_ZeroInputDuration(t *testing.T) {
 	assert.Equal(t, time.Duration(0), DurationWithPositiveJitter(time.Duration(0), 0.5))
 }
 
+func TestDurationWithPositiveJitter_SmallInputDuration(t *testing.T) {
+	assert.Equal(t, time.Duration(0), DurationWithPositiveJitter(time.Duration(7), 0.1))
+}
+
 func TestDurationWithNegativeJitter(t *testing.T) {
 	const numRuns = 1000
 
@@ -100,6 +108,10 @@ func TestDurationWithNegativeJitter_ZeroInputDuration(t *testing.T) {
 	assert.Equal(t, time.Duration(0), DurationWithNegativeJitter(time.Duration(0), 0.5))
 }
 
+func TestDurationWithNegativeJitter_SmallInputDuration(t *testing.T) {
+	assert.Equal(t, time.Duration(0), DurationWithNegativeJitter(time.Duration(7), 0.1))
+}
+
 func TestParseTime(t *testing.T) {
 	var tests = []struct {
 		input  string