Re-enqueue 429 requests if there are multiple query-schedulers

CHANGELOG.md

@@ -24,6 +24,7 @@
 * [FEATURE] Store Gateway: Add `-store-gateway.sharding-ring.keep-instance-in-the-ring-on-shutdown` to skip unregistering instance from the ring in shutdown. #5421
 * [FEATURE] Ruler: Support for filtering rules in the API. #5417
 * [FEATURE] Compactor: Add `-compactor.ring.tokens-file-path` to store generated tokens locally. #5432
+* [FEATURE] Query Frontend: Add `-frontend.retry-on-too-many-outstanding-requests` to re-enqueue 429 requests if there are multiple query-schedulers available. #5496
 * [ENHANCEMENT] Distributor/Ingester: Add span on push path #5319
 * [ENHANCEMENT] Support object storage backends for runtime configuration file. #5292
 * [ENHANCEMENT] Query Frontend: Reject subquery with too small step size. #5323

docs/configuration/config-file-reference.md

@@ -3528,6 +3528,11 @@ grpc_client_config:
   # CLI flag: -frontend.grpc-client-config.tls-insecure-skip-verify
   [tls_insecure_skip_verify: <boolean> | default = false]
 
+# When multiple query-schedulers are available, re-enqueue queries that were
+# rejected due to too many outstanding requests.
+# CLI flag: -frontend.retry-on-too-many-outstanding-requests
+[retry_on_too_many_outstanding_requests: <boolean> | default = false]
+
 # Name of network interface to read address from. This address is sent to
 # query-scheduler and querier, which uses it to send the query response back to
 # query-frontend.

pkg/frontend/v2/frontend.go

@@ -30,10 +30,11 @@ import (
 
 // Config for a Frontend.
 type Config struct {
-	SchedulerAddress  string            `yaml:"scheduler_address"`
-	DNSLookupPeriod   time.Duration     `yaml:"scheduler_dns_lookup_period"`
-	WorkerConcurrency int               `yaml:"scheduler_worker_concurrency"`
-	GRPCClientConfig  grpcclient.Config `yaml:"grpc_client_config"`
+	SchedulerAddress                  string            `yaml:"scheduler_address"`
+	DNSLookupPeriod                   time.Duration     `yaml:"scheduler_dns_lookup_period"`
+	WorkerConcurrency                 int               `yaml:"scheduler_worker_concurrency"`
+	GRPCClientConfig                  grpcclient.Config `yaml:"grpc_client_config"`
+	RetryOnTooManyOutstandingRequests bool              `yaml:"retry_on_too_many_outstanding_requests"`
 
 	// Used to find local IP address, that is sent to scheduler and querier-worker.
 	InfNames []string `yaml:"instance_interface_names"`
@@ -47,6 +48,7 @@ func (cfg *Config) RegisterFlags(f *flag.FlagSet) {
 	f.StringVar(&cfg.SchedulerAddress, "frontend.scheduler-address", "", "DNS hostname used for finding query-schedulers.")
 	f.DurationVar(&cfg.DNSLookupPeriod, "frontend.scheduler-dns-lookup-period", 10*time.Second, "How often to resolve the scheduler-address, in order to look for new query-scheduler instances.")
 	f.IntVar(&cfg.WorkerConcurrency, "frontend.scheduler-worker-concurrency", 5, "Number of concurrent workers forwarding queries to single query-scheduler.")
+	f.BoolVar(&cfg.RetryOnTooManyOutstandingRequests, "frontend.retry-on-too-many-outstanding-requests", false, "When multiple query-schedulers are available, re-enqueue queries that were rejected due to too many outstanding requests.")
 
 	cfg.InfNames = []string{"eth0", "en0"}
 	f.Var((*flagext.StringSlice)(&cfg.InfNames), "frontend.instance-interface-names", "Name of network interface to read address from. This address is sent to query-scheduler and querier, which uses it to send the query response back to query-frontend.")
@@ -86,6 +88,8 @@ type frontendRequest struct {
 
 	enqueue  chan enqueueResult
 	response chan *frontendv2pb.QueryResultRequest
+
+	retryOnTooManyOutstandingRequests bool
 }
 
 type enqueueStatus int
@@ -192,6 +196,8 @@ func (f *Frontend) RoundTripGRPC(ctx context.Context, req *httpgrpc.HTTPRequest)
 		// even if this goroutine goes away due to client context cancellation.
 		enqueue:  make(chan enqueueResult, 1),
 		response: make(chan *frontendv2pb.QueryResultRequest, 1),
+
+		retryOnTooManyOutstandingRequests: f.cfg.RetryOnTooManyOutstandingRequests && f.schedulerWorkers.getWorkersCount() > 1,
 	}
 
 	f.requests.put(freq)

pkg/frontend/v2/frontend_scheduler_worker.go

@@ -296,12 +296,16 @@ func (w *frontendSchedulerWorker) schedulerLoop(loop schedulerpb.SchedulerForFro
 				}
 
 			case schedulerpb.TOO_MANY_REQUESTS_PER_TENANT:
-				req.enqueue <- enqueueResult{status: waitForResponse}
-				req.response <- &frontendv2pb.QueryResultRequest{
-					HttpResponse: &httpgrpc.HTTPResponse{
-						Code: http.StatusTooManyRequests,
-						Body: []byte("too many outstanding requests"),
-					},
+				if req.retryOnTooManyOutstandingRequests {
+					req.enqueue <- enqueueResult{status: failed}
+				} else {
+					req.enqueue <- enqueueResult{status: waitForResponse}
+					req.response <- &frontendv2pb.QueryResultRequest{
+						HttpResponse: &httpgrpc.HTTPResponse{
+							Code: http.StatusTooManyRequests,
+							Body: []byte("too many outstanding requests"),
+						},
+					}
 				}
 			}