fix(checker): Add cap on metric fetching to prevent checker OOM

Closes #190

checker/trigger_checker.go

@@ -9,6 +9,12 @@ import (
 	"github.com/moira-alert/moira/metrics"
 )
 
+const (
+	// Prevents OOM when a trigger has enormous TTL,
+	// see https://github.com/moira-alert/moira/pull/519 for details
+	safeMetricFetchIntervalSeconds = 7 * 24 * 3600
+)
+
 // TriggerChecker represents data, used for handling new trigger state
 type TriggerChecker struct {
 	database moira.Database
@@ -101,7 +107,7 @@ func getTTLState(triggerTTLState *moira.TTLState) moira.TTLState {
 
 func calculateFrom(lastCheckTimestamp, triggerTTL int64) int64 {
 	if triggerTTL != 0 {
-		return lastCheckTimestamp - triggerTTL
+		return lastCheckTimestamp - moira.MinInt64(triggerTTL, safeMetricFetchIntervalSeconds)
 	}
 	return lastCheckTimestamp - 600
 }

checker/trigger_checker_test.go

@@ -2,6 +2,7 @@ package checker
 
 import (
 	"fmt"
+	"math"
 	"testing"
 
 	"github.com/golang/mock/gomock"
@@ -195,4 +196,28 @@ func TestInitTriggerChecker(t *testing.T) {
 		}
 		So(*actual, ShouldResemble, expected)
 	})
+
+	trigger.TTL = math.MaxInt64
+
+	Convey("Test trigger with enormous ttl", t, func() {
+		dataBase.EXPECT().GetTrigger(triggerID).Return(trigger, nil)
+		dataBase.EXPECT().GetTriggerLastCheck(triggerID).Return(lastCheck, nil)
+		actual, err := MakeTriggerChecker(triggerID, dataBase, logger, config, metricSource.CreateMetricSourceProvider(localSource, nil), &metrics.CheckerMetrics{})
+		So(err, ShouldBeNil)
+
+		expected := TriggerChecker{
+			triggerID: triggerID,
+			database:  dataBase,
+			config:    config,
+			source:    localSource,
+			logger:    logger,
+			trigger:   &trigger,
+			ttl:       math.MaxInt64,
+			ttlState:  moira.TTLStateNODATA,
+			lastCheck: &lastCheck,
+			from:      lastCheck.Timestamp - safeMetricFetchIntervalSeconds,
+			until:     actual.until,
+		}
+		So(*actual, ShouldResemble, expected)
+	})
 }

helpers.go

@@ -195,3 +195,10 @@ func ChunkSlice(original []string, chunkSize int) (divided [][]string) {
 func RoundToNearestRetention(ts, retention int64) int64 {
 	return (ts + retention/2) / retention * retention
 }
+
+func MinInt64(a, b int64) int64 {
+	if a < b {
+		return a
+	}
+	return b
+}