Return 503 on hitting distributor instance limits

CHANGELOG.md

@@ -40,6 +40,7 @@
 * [ENHANCEMENT] StoreGateway: Add new `cortex_bucket_store_chunk_pool_inuse_bytes` metric to track the usage in chunk pool. #6310
 * [ENHANCEMENT] Distributor: Add new `cortex_distributor_inflight_client_requests` metric to track number of ingester client inflight requests. #6358
 * [ENHANCEMENT] Distributor: Expose `cortex_label_size_bytes` native histogram metric. #6372
+* [ENHANCEMENT] Distributor: Return HTTP 5XX instead of HTTP 4XX when instance limits are hit. #6358
 * [BUGFIX] Runtime-config: Handle absolute file paths when working directory is not / #6224
 * [BUGFIX] Ruler: Allow rule evaluation to complete during shutdown. #6326
 * [BUGFIX] Ring: update ring with new ip address when instance is lost, rejoins, but heartbeat is disabled  #6271

pkg/distributor/distributor.go

@@ -51,11 +51,6 @@ var (
 	// Validation errors.
 	errInvalidShardingStrategy = errors.New("invalid sharding strategy")
 	errInvalidTenantShardSize  = errors.New("invalid tenant shard size. The value must be greater than or equal to 0")
-
-	// Distributor instance limits errors.
-	errTooManyInflightPushRequests    = errors.New("too many inflight push requests in distributor")
-	errMaxSamplesPushRateLimitReached = errors.New("distributor's samples push rate limit reached")
-	errTooManyInflightClientRequests  = errors.New("too many inflight ingester client requests in distributor")
 )
 
 const (
@@ -668,19 +663,19 @@ func (d *Distributor) Push(ctx context.Context, req *cortexpb.WriteRequest) (*co
 	d.incomingMetadata.WithLabelValues(userID).Add(float64(len(req.Metadata)))
 
 	if d.cfg.InstanceLimits.MaxInflightPushRequests > 0 && inflight > int64(d.cfg.InstanceLimits.MaxInflightPushRequests) {
-		return nil, errTooManyInflightPushRequests
+		return nil, httpgrpc.Errorf(http.StatusServiceUnavailable, "too many inflight push requests in distributor")
 	}
 
 	if d.cfg.InstanceLimits.MaxIngestionRate > 0 {
 		if rate := d.ingestionRate.Rate(); rate >= d.cfg.InstanceLimits.MaxIngestionRate {
-			return nil, errMaxSamplesPushRateLimitReached
+			return nil, httpgrpc.Errorf(http.StatusServiceUnavailable, "distributor's samples push rate limit reached")
 		}
 	}
 
 	// only reject requests at this stage to allow distributor to finish sending the current batch request to all ingesters
 	// even if we've exceeded the MaxInflightClientRequests in the `doBatch`
 	if d.cfg.InstanceLimits.MaxInflightClientRequests > 0 && d.inflightClientRequests.Load() > int64(d.cfg.InstanceLimits.MaxInflightClientRequests) {
-		return nil, errTooManyInflightClientRequests
+		return nil, httpgrpc.Errorf(http.StatusServiceUnavailable, "too many inflight ingester client requests in distributor")
 	}
 
 	removeReplica := false

pkg/distributor/distributor_test.go

@@ -840,7 +840,7 @@ func TestDistributor_PushInstanceLimits(t *testing.T) {
 			preInflight:   101,
 			inflightLimit: 101,
 			pushes: []testPush{
-				{samples: 100, expectedError: errTooManyInflightPushRequests},
+				{samples: 100, expectedError: httpgrpc.Errorf(http.StatusServiceUnavailable, "too many inflight push requests in distributor")},
 			},
 		},
 		"below inflight client limit": {
@@ -863,7 +863,8 @@ func TestDistributor_PushInstanceLimits(t *testing.T) {
 			preInflightClient:   103,
 			inflightClientLimit: 101,
 			pushes: []testPush{
-				{samples: 100, expectedError: errTooManyInflightClientRequests},
+				{samples: 100, expectedError: httpgrpc.Errorf(http.StatusServiceUnavailable,
+					"too many inflight ingester client requests in distributor")},
 			},
 		},
 		"below ingestion rate limit": {
@@ -892,7 +893,7 @@ func TestDistributor_PushInstanceLimits(t *testing.T) {
 			ingestionRateLimit: 1000,
 
 			pushes: []testPush{
-				{samples: 100, expectedError: errMaxSamplesPushRateLimitReached},
+				{samples: 100, expectedError: httpgrpc.Errorf(http.StatusServiceUnavailable, "distributor's samples push rate limit reached")},
 				{samples: 100, expectedError: nil},
 			},
 		},
@@ -902,10 +903,10 @@ func TestDistributor_PushInstanceLimits(t *testing.T) {
 			ingestionRateLimit: 1000,
 
 			pushes: []testPush{
-				{samples: 5000, expectedError: nil},                               // after push, rate = 500 + 0.2*(5000-500) = 1400
-				{samples: 5000, expectedError: errMaxSamplesPushRateLimitReached}, // after push, rate = 1400 + 0.2*(0 - 1400) = 1120
-				{samples: 5000, expectedError: errMaxSamplesPushRateLimitReached}, // after push, rate = 1120 + 0.2*(0 - 1120) = 896
-				{samples: 5000, expectedError: nil},                               // 896 is below 1000, so this push succeeds, new rate = 896 + 0.2*(5000-896) = 1716.8
+				{samples: 5000, expectedError: nil}, // after push, rate = 500 + 0.2*(5000-500) = 1400
+				{samples: 5000, expectedError: httpgrpc.Errorf(http.StatusServiceUnavailable, "distributor's samples push rate limit reached")}, // after push, rate = 1400 + 0.2*(0 - 1400) = 1120
+				{samples: 5000, expectedError: httpgrpc.Errorf(http.StatusServiceUnavailable, "distributor's samples push rate limit reached")}, // after push, rate = 1120 + 0.2*(0 - 1120) = 896
+				{samples: 5000, expectedError: nil}, // 896 is below 1000, so this push succeeds, new rate = 896 + 0.2*(5000-896) = 1716.8
 			},
 		},
 	}