Create new cortex_querier_codec_response_size histogram to track the size of the encoded Query responses

CHANGELOG.md

@@ -50,6 +50,7 @@
 * [ENHANCEMENT] Ingester: Make sure unregistered ingester joining the ring after WAL replay. #6277
 * [ENHANCEMENT] Distributor: Add a new `-distributor.num-push-workers` flag to use a goroutine worker pool when sending data from distributor to ingesters. #6406
 * [ENHANCEMENT] Ingester: If a limit per label set entry doesn't have any label, use it as the default partition to catch all series that doesn't match any other label sets entries. #6435
+* [ENHANCEMENT] Querier: Add new `cortex_querier_codec_response_size` metric to track the size of the encoded query responses from queriers. #6444
 * [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/api/handlers.go

@@ -231,11 +231,15 @@ func NewQuerierHandler(
 		nil,
 		false,
 	)
+	// Let's clear all codecs to create the instrumented ones
+	api.ClearCodecs()
+	cm := codec.NewInstrumentedCodecMetrics(reg)
 
-	// JSON codec is already installed. Install Protobuf codec to give the option for using either.
-	api.InstallCodec(codec.ProtobufCodec{CortexInternal: false})
+	api.InstallCodec(codec.NewInstrumentedCodec(v1.JSONCodec{}, cm))
+	// Install Protobuf codec to give the option for using either.
+	api.InstallCodec(codec.NewInstrumentedCodec(codec.ProtobufCodec{CortexInternal: false}, cm))
 	// Protobuf codec for Cortex internal requests. This should be used by Cortex Ruler only for remote evaluation.
-	api.InstallCodec(codec.ProtobufCodec{CortexInternal: true})
+	api.InstallCodec(codec.NewInstrumentedCodec(codec.ProtobufCodec{CortexInternal: true}, cm))
 
 	router := mux.NewRouter()
 

pkg/querier/codec/instrumented_codec.go

@@ -0,0 +1,57 @@
+package codec
+
+import (
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+	v1 "github.com/prometheus/prometheus/web/api/v1"
+	"github.com/weaveworks/common/middleware"
+)
+
+type InstrumentedCodecMetrics struct {
+	responseSizeHistogram *prometheus.HistogramVec
+}
+
+func NewInstrumentedCodecMetrics(reg prometheus.Registerer) *InstrumentedCodecMetrics {
+	return &InstrumentedCodecMetrics{
+		responseSizeHistogram: promauto.With(reg).NewHistogramVec(prometheus.HistogramOpts{
+			Namespace:                       "cortex",
+			Name:                            "querier_codec_response_size",
+			Help:                            "Size of the encoded prometheus response from the queriers.",
+			Buckets:                         middleware.BodySizeBuckets,
+			NativeHistogramBucketFactor:     1.1,
+			NativeHistogramMaxBucketNumber:  100,
+			NativeHistogramMinResetDuration: time.Hour,
+		}, []string{"content_type"}),
+	}
+}
+
+type InstrumentedCodec struct {
+	uc v1.Codec
+
+	metrics *InstrumentedCodecMetrics
+}
+
+func (c *InstrumentedCodec) ContentType() v1.MIMEType {
+	return c.uc.ContentType()
+}
+
+func (c *InstrumentedCodec) CanEncode(resp *v1.Response) bool {
+	return c.uc.CanEncode(resp)
+}
+
+func (c *InstrumentedCodec) Encode(resp *v1.Response) ([]byte, error) {
+	b, err := c.uc.Encode(resp)
+	if err == nil {
+		c.metrics.responseSizeHistogram.WithLabelValues(c.uc.ContentType().String()).Observe(float64(len((b))))
+	}
+	return b, err
+}
+
+func NewInstrumentedCodec(uc v1.Codec, m *InstrumentedCodecMetrics) v1.Codec {
+	return &InstrumentedCodec{
+		uc:      uc,
+		metrics: m,
+	}
+}

pkg/querier/codec/protobuf_codec_test.go

@@ -1,9 +1,13 @@
 package codec
 
 import (
+	"bytes"
+	"fmt"
 	"testing"
 
 	"github.com/gogo/protobuf/proto"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/testutil"
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/prometheus/model/histogram"
 	"github.com/prometheus/prometheus/model/labels"
@@ -437,7 +441,9 @@ func TestProtobufCodec_Encode(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			codec := ProtobufCodec{CortexInternal: test.cortexInternal}
+			reg := prometheus.NewPedanticRegistry()
+			cm := NewInstrumentedCodecMetrics(reg)
+			codec := NewInstrumentedCodec(ProtobufCodec{CortexInternal: test.cortexInternal}, cm)
 			body, err := codec.Encode(&v1.Response{
 				Status: tripperware.StatusSuccess,
 				Data:   test.data,
@@ -446,6 +452,21 @@ func TestProtobufCodec_Encode(t *testing.T) {
 			b, err := proto.Marshal(test.expected)
 			require.NoError(t, err)
 			require.Equal(t, string(b), string(body))
+			require.NoError(t, testutil.GatherAndCompare(reg, bytes.NewBufferString(fmt.Sprintf(`
+				# HELP cortex_querier_codec_response_size Size of the encoded prometheus response from the queriers.
+				# TYPE cortex_querier_codec_response_size histogram
+				cortex_querier_codec_response_size_bucket{content_type="`+codec.ContentType().String()+`",le="1.048576e+06"} 1
+				cortex_querier_codec_response_size_bucket{content_type="`+codec.ContentType().String()+`",le="2.62144e+06"} 1
+				cortex_querier_codec_response_size_bucket{content_type="`+codec.ContentType().String()+`",le="5.24288e+06"} 1
+				cortex_querier_codec_response_size_bucket{content_type="`+codec.ContentType().String()+`",le="1.048576e+07"} 1
+				cortex_querier_codec_response_size_bucket{content_type="`+codec.ContentType().String()+`",le="2.62144e+07"} 1
+				cortex_querier_codec_response_size_bucket{content_type="`+codec.ContentType().String()+`",le="5.24288e+07"} 1
+				cortex_querier_codec_response_size_bucket{content_type="`+codec.ContentType().String()+`",le="1.048576e+08"} 1
+				cortex_querier_codec_response_size_bucket{content_type="`+codec.ContentType().String()+`",le="2.62144e+08"} 1
+				cortex_querier_codec_response_size_bucket{content_type="`+codec.ContentType().String()+`",le="+Inf"} 1
+				cortex_querier_codec_response_size_sum{content_type="`+codec.ContentType().String()+`"} %v
+				cortex_querier_codec_response_size_count{content_type="`+codec.ContentType().String()+`"} 1
+	`, len(body))), "cortex_querier_codec_response_size"))
 		})
 	}
 }