Alerting: Set MissingSeriesEvalsToResolve to 1 for Prometheus-imported rules (#101973)

pkg/services/ngalert/prom/convert.go

@@ -241,6 +241,12 @@ func (p *Converter) convertRule(orgID int64, namespaceUID string, promGroup Prom
 		RuleGroup:    promGroup.Name,
 		IsPaused:     isPaused,
 		Record:       record,
+
+		// MissingSeriesEvalsToResolve is set to 1 to match the Prometheus behaviour.
+		// Prometheus resolves alerts as soon as the series disappears.
+		// By setting this value to 1 we ensure that the alert is resolved on the first evaluation
+		// that doesn't have the series.
+		MissingSeriesEvalsToResolve: util.Pointer(1),
 	}
 
 	if p.cfg.KeepOriginalRuleDefinition != nil && *p.cfg.KeepOriginalRuleDefinition {

pkg/services/ngalert/prom/convert_test.go

@@ -280,6 +280,7 @@ func TestPrometheusRulesToGrafana(t *testing.T) {
 
 				require.Equal(t, models.Duration(evalOffset), grafanaRule.Data[0].RelativeTimeRange.To)
 				require.Equal(t, models.Duration(10*time.Minute+evalOffset), grafanaRule.Data[0].RelativeTimeRange.From)
+				require.Equal(t, util.Pointer(1), grafanaRule.MissingSeriesEvalsToResolve)
 
 				originalRuleDefinition, err := yaml.Marshal(promRule)
 				require.NoError(t, err)