map gRPC codes.Cancled to 499, not 500 in querier

CHANGELOG.md

@@ -81,6 +81,7 @@
 * [BUGFIX] Querier/Query Frontend: Fix DNS watcher dropping all query-frontend/scheduler worker connections on a transient DNS lookup failure. #7698
 * [BUGFIX] Ring: Fix DynamoDB KV CAS not retrying on transactional conditional check failures. `TransactWriteItems` reports condition failures as `TransactionCanceledException` with a `ConditionalCheckFailed` cancellation reason, which was not recognized as retryable, so any concurrent ring update conflict (e.g. many ingesters joining during a rolling update) failed immediately instead of re-reading and retrying. `TransactionConflict` cancellation reasons are also treated as retryable. #7706
 * [BUGFIX] Distributor: Return HTTP 499 (Client Closed Request) instead of 500 when a remote-write or OTLP push is canceled by the client, so client-side cancellations are no longer counted as server-side errors. #7717
+* [BUGFIX] Querier: Fix gRPC `codes.Canceled` errors being mapped to HTTP 500 instead of 499 when a client cancels a query. #7738
 
 ## 1.21.1 2026-06-04
 

pkg/querier/error_translate_queryable.go

@@ -10,6 +10,7 @@ import (
 	"github.com/prometheus/prometheus/promql"
 	"github.com/prometheus/prometheus/storage"
 	"github.com/prometheus/prometheus/util/annotations"
+	"google.golang.org/grpc/codes"
 
 	"github.com/cortexproject/cortex/pkg/util/validation"
 )
@@ -46,7 +47,7 @@ func TranslateToPromqlAPIError(err error) error {
 		return err
 	default:
 		if errors.Is(err, context.Canceled) {
-			return err // 422
+			return err // 499
 		}
 
 		if search.IsResourceExhausted(err) {
@@ -63,6 +64,12 @@ func TranslateToPromqlAPIError(err error) error {
 		if ok {
 			code := s.Code()
 
+			// gRPC context cancellation (codes.Canceled) should be treated as a canceled query,
+			// not as a storage error (500).
+			if code == codes.Canceled {
+				return promql.ErrQueryCanceled("grpc context canceled")
+			}
+
 			// Treat these as HTTP status codes, even though they are supposed to be grpc codes.
 			if code >= 400 && code < 500 {
 				// Return directly, will be mapped to 422

pkg/querier/error_translate_queryable_test.go

@@ -24,6 +24,8 @@ import (
 	"github.com/stretchr/testify/require"
 	"github.com/weaveworks/common/httpgrpc"
 	"github.com/weaveworks/common/user"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 
 	"github.com/cortexproject/cortex/pkg/storegateway"
 	"github.com/cortexproject/cortex/pkg/util/limiter"
@@ -126,6 +128,16 @@ func TestApiStatusCodes(t *testing.T) {
 			expectedString: limiter.ErrResourceLimitReachedStr,
 			expectedCode:   500,
 		},
+		{
+			err:            status.Error(codes.Canceled, "context canceled"),
+			expectedString: "query was canceled",
+			expectedCode:   499,
+		},
+		{
+			err:            errors.Wrap(status.Error(codes.Canceled, "context canceled"), "wrapped grpc error"),
+			expectedString: "query was canceled",
+			expectedCode:   499,
+		},
 	} {
 		for k, q := range map[string]storage.SampleAndChunkQueryable{
 			"error from queryable": errorTestQueryable{err: tc.err},