elastic: always use millisecond-intervals for alerting (#54157) (#54317)

(cherry picked from commit a58edc9f5e)

Co-authored-by: Gábor Farkas <gabor.farkas@gmail.com>

pkg/tsdb/elasticsearch/time_series_query.go

@@ -251,7 +251,14 @@ func addDateHistogramAgg(aggBuilder es.AggBuilder, bucketAgg *BucketAgg, timeFro
 		a.Format = bucketAgg.Settings.Get("format").MustString(es.DateFormatEpochMS)
 
 		if a.FixedInterval == "auto" {
-			a.FixedInterval = "$__interval"
+			// note this is not really a valid grafana-variable-handling,
+			// because normally this would not match `$__interval_ms`,
+			// but because how we apply these in the go-code, this will work
+			// correctly, and becomes something like `500ms`.
+			// a nicer way would be to use `${__interval_ms}ms`, but
+			// that format is not recognized where we apply these variables
+			// in the elasticsearch datasource
+			a.FixedInterval = "$__interval_msms"
 		}
 
 		if offset, err := bucketAgg.Settings.Get("offset").String(); err == nil {

pkg/tsdb/elasticsearch/time_series_query_test.go

@@ -399,7 +399,7 @@ func TestExecuteTimeSeriesQuery(t *testing.T) {
 			require.Equal(t, firstLevel.Aggregation.Type, "date_histogram")
 			hAgg := firstLevel.Aggregation.Aggregation.(*es.DateHistogramAgg)
 			require.Equal(t, hAgg.Field, "@timestamp")
-			require.Equal(t, hAgg.FixedInterval, "$__interval")
+			require.Equal(t, hAgg.FixedInterval, "$__interval_msms")
 			require.Equal(t, hAgg.MinDocCount, 2)
 
 			t.Run("Should not include time_zone when timeZone is utc", func(t *testing.T) {