[r310] query-frontend: Do not break scheduler connection on malformed queries

pkg/frontend/v2/frontend.go

@@ -144,6 +144,9 @@ const (
 
 type enqueueResult struct {
 	status enqueueStatus
+	// If the status is failed and if it was because of a client error on the frontend,
+	// the clientErr should be updated with the appropriate error.
+	clientErr error
 
 	cancelCh chan<- uint64 // Channel that can be used for request cancellation. If nil, cancellation is not possible.
 }
@@ -285,6 +288,11 @@ enqueueAgain:
 			cancelCh = enqRes.cancelCh
 			break // go wait for response.
 		} else if enqRes.status == failed {
+			if enqRes.clientErr != nil {
+				// It failed because of a client error. No need to retry.
+				return nil, nil, httpgrpc.Errorf(http.StatusBadRequest, "failed to enqueue request: %s", enqRes.clientErr.Error())
+			}
+
 			retries--
 			if retries > 0 {
 				spanLogger.DebugLog("msg", "enqueuing request failed, will retry")

pkg/frontend/v2/frontend_scheduler_worker.go

@@ -412,8 +412,8 @@ func (w *frontendSchedulerWorker) enqueueRequest(loop schedulerpb.SchedulerForFr
 	frontendToSchedulerRequest, err := w.toSchedulerAdapter.frontendToSchedulerEnqueueRequest(req, w.frontendAddr)
 	if err != nil {
 		level.Warn(spanLogger).Log("msg", "error converting frontend request to scheduler request", "err", err)
-		req.enqueue <- enqueueResult{status: failed}
-		return err
+		req.enqueue <- enqueueResult{status: failed, clientErr: err}
+		return nil
 	}
 
 	err = loop.Send(frontendToSchedulerRequest)

pkg/frontend/v2/frontend_test.go

@@ -242,17 +242,59 @@ func TestFrontendTooManyRequests(t *testing.T) {
 	require.Equal(t, int32(http.StatusTooManyRequests), resp.Code)
 }
 
-func TestFrontendEnqueueFailure(t *testing.T) {
-	f, _ := setupFrontend(t, nil, func(*Frontend, *schedulerpb.FrontendToScheduler) *schedulerpb.SchedulerToFrontend {
-		return &schedulerpb.SchedulerToFrontend{Status: schedulerpb.SHUTTING_DOWN}
+func TestFrontendEnqueueFailures(t *testing.T) {
+	t.Run("scheduler is shutting down with valid query", func(t *testing.T) {
+		f, _ := setupFrontend(t, nil, func(*Frontend, *schedulerpb.FrontendToScheduler) *schedulerpb.SchedulerToFrontend {
+			return &schedulerpb.SchedulerToFrontend{Status: schedulerpb.SHUTTING_DOWN}
+		})
+
+		req := &httpgrpc.HTTPRequest{
+			Url: "/api/v1/query_range?start=946684800&end=946771200&step=60&query=up",
+		}
+		_, _, err := f.RoundTripGRPC(user.InjectOrgID(context.Background(), "test"), req)
+		require.Error(t, err)
+		require.True(t, strings.Contains(err.Error(), "failed to enqueue request"))
 	})
+	t.Run("scheduler is running fine", func(t *testing.T) {
+		f, _ := setupFrontend(t, nil, func(*Frontend, *schedulerpb.FrontendToScheduler) *schedulerpb.SchedulerToFrontend {
+			return &schedulerpb.SchedulerToFrontend{Status: schedulerpb.OK}
+		})
 
-	req := &httpgrpc.HTTPRequest{
-		Url: "/api/v1/query_range?start=946684800&end=946771200&step=60",
-	}
-	_, _, err := f.RoundTripGRPC(user.InjectOrgID(context.Background(), "test"), req)
-	require.Error(t, err)
-	require.True(t, strings.Contains(err.Error(), "failed to enqueue request"))
+		cases := []struct {
+			name, url, error string
+		}{
+			{
+				name:  "start time is wrong",
+				url:   "/api/v1/query_range?start=9466camnsd84800&end=946771200&step=60&query=up{}",
+				error: `rpc error: code = Code(400) desc = failed to enqueue request: invalid parameter "start": cannot parse "9466camnsd84800" to a valid timestamp`,
+			},
+			{
+				name:  "end time is wrong",
+				url:   "/api/v1/query_range?start=946684800&end=946771200dgiu&step=60&query=up{}",
+				error: `rpc error: code = Code(400) desc = failed to enqueue request: invalid parameter "end": cannot parse "946771200dgiu" to a valid timestamp`,
+			},
+			{
+				name:  "query time is wrong",
+				url:   "/api/v1/query_range?start=946684800&end=946771200&step=60&query=up{",
+				error: `rpc error: code = Code(400) desc = failed to enqueue request: invalid parameter "query": 1:4: parse error: unexpected end of input inside braces`,
+			},
+			{
+				name:  "no query provided",
+				url:   "/api/v1/query_range?start=946684800&end=946771200&step=60",
+				error: `rpc error: code = Code(400) desc = failed to enqueue request: invalid parameter "query": unknown position: parse error: no expression found in input`,
+			},
+		}
+		for _, c := range cases {
+			t.Run(c.name, func(t *testing.T) {
+				req := &httpgrpc.HTTPRequest{
+					Url: c.url,
+				}
+				_, _, err := f.RoundTripGRPC(user.InjectOrgID(context.Background(), "test"), req)
+				require.Error(t, err)
+				require.Equal(t, c.error, err.Error())
+			})
+		}
+	})
 }
 
 func TestFrontendCancellation(t *testing.T) {