From 3e737ddcccce1521411c54a979feb1e9f5efd25f Mon Sep 17 00:00:00 2001
From: JBD <jbd@amazon.com>
Date: Wed, 26 May 2021 15:06:47 -0700
Subject: [PATCH] Log dropped metric count when exporting from PRW exporter

Fixes https://github.com/open-telemetry/wg-prometheus/issues/13.
---
 exporter/prometheusremotewriteexporter/exporter.go      | 8 ++++++--
 exporter/prometheusremotewriteexporter/exporter_test.go | 9 +++++----
 exporter/prometheusremotewriteexporter/factory.go       | 2 +-
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/exporter/prometheusremotewriteexporter/exporter.go b/exporter/prometheusremotewriteexporter/exporter.go
index 4e50ca44eb8..fd35c4fc65a 100644
--- a/exporter/prometheusremotewriteexporter/exporter.go
+++ b/exporter/prometheusremotewriteexporter/exporter.go
@@ -31,6 +31,7 @@ import (
 	"github.com/gogo/protobuf/proto"
 	"github.com/golang/snappy"
 	"github.com/prometheus/prometheus/prompb"
+	"go.uber.org/zap"
 
 	"go.opentelemetry.io/collector/component"
 	"go.opentelemetry.io/collector/config/confighttp"
@@ -51,10 +52,11 @@ type PRWExporter struct {
 	concurrency     int
 	userAgentHeader string
 	clientSettings  *confighttp.HTTPClientSettings
+	logger          *zap.Logger
 }
 
 // NewPRWExporter initializes a new PRWExporter instance and sets fields accordingly.
-func NewPRWExporter(cfg *Config, buildInfo component.BuildInfo) (*PRWExporter, error) {
+func NewPRWExporter(cfg *Config, buildInfo component.BuildInfo, logger *zap.Logger) (*PRWExporter, error) {
 	sanitizedLabels, err := validateAndSanitizeExternalLabels(cfg.ExternalLabels)
 	if err != nil {
 		return nil, err
@@ -76,6 +78,7 @@ func NewPRWExporter(cfg *Config, buildInfo component.BuildInfo) (*PRWExporter, e
 		userAgentHeader: userAgentHeader,
 		concurrency:     cfg.RemoteWriteQueue.NumConsumers,
 		clientSettings:  &cfg.HTTPClientSettings,
+		logger:          logger,
 	}, nil
 }
 
@@ -158,7 +161,8 @@ func (prwe *PRWExporter) PushMetrics(ctx context.Context, md pdata.Metrics) erro
 			errs = append(errs, exportErrors...)
 		}
 
-		if dropped != 0 {
+		if dropped > 0 {
+			prwe.logger.Info("Prometheus remote write dropped metrics", zap.Int("dropped_count", dropped))
 			return consumererror.Combine(errs)
 		}
 
diff --git a/exporter/prometheusremotewriteexporter/exporter_test.go b/exporter/prometheusremotewriteexporter/exporter_test.go
index 1eda3f6e9b8..b6300669774 100644
--- a/exporter/prometheusremotewriteexporter/exporter_test.go
+++ b/exporter/prometheusremotewriteexporter/exporter_test.go
@@ -28,6 +28,7 @@ import (
 	"github.com/prometheus/prometheus/prompb"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"go.uber.org/zap"
 
 	"go.opentelemetry.io/collector/component"
 	"go.opentelemetry.io/collector/component/componenttest"
@@ -110,7 +111,7 @@ func Test_NewPRWExporter(t *testing.T) {
 			cfg.ExternalLabels = tt.externalLabels
 			cfg.Namespace = tt.namespace
 			cfg.RemoteWriteQueue.NumConsumers = 1
-			prwe, err := NewPRWExporter(cfg, tt.buildInfo)
+			prwe, err := NewPRWExporter(cfg, tt.buildInfo, zap.NewNop())
 
 			if tt.returnErrorOnCreate {
 				assert.Error(t, err)
@@ -191,7 +192,7 @@ func Test_Start(t *testing.T) {
 			cfg.RemoteWriteQueue.NumConsumers = 1
 			cfg.HTTPClientSettings = tt.clientSettings
 
-			prwe, err := NewPRWExporter(cfg, tt.buildInfo)
+			prwe, err := NewPRWExporter(cfg, tt.buildInfo, zap.NewNop())
 			assert.NoError(t, err)
 			assert.NotNil(t, prwe)
 
@@ -333,7 +334,7 @@ func runExportPipeline(ts *prompb.TimeSeries, endpoint *url.URL) []error {
 		Version:     "1.0",
 	}
 	// after this, instantiate a CortexExporter with the current HTTP client and endpoint set to passed in endpoint
-	prwe, err := NewPRWExporter(cfg, buildInfo)
+	prwe, err := NewPRWExporter(cfg, buildInfo, zap.NewNop())
 	if err != nil {
 		errs = append(errs, err)
 		return errs
@@ -591,7 +592,7 @@ func Test_PushMetrics(t *testing.T) {
 				Description: "OpenTelemetry Collector",
 				Version:     "1.0",
 			}
-			prwe, nErr := NewPRWExporter(cfg, buildInfo)
+			prwe, nErr := NewPRWExporter(cfg, buildInfo, zap.NewNop())
 			require.NoError(t, nErr)
 			require.NoError(t, prwe.Start(context.Background(), componenttest.NewNopHost()))
 			err := prwe.PushMetrics(context.Background(), *tt.md)
diff --git a/exporter/prometheusremotewriteexporter/factory.go b/exporter/prometheusremotewriteexporter/factory.go
index 6b9b2c155a1..4e46348074c 100644
--- a/exporter/prometheusremotewriteexporter/factory.go
+++ b/exporter/prometheusremotewriteexporter/factory.go
@@ -45,7 +45,7 @@ func createMetricsExporter(_ context.Context, params component.ExporterCreatePar
 		return nil, errors.New("invalid configuration")
 	}
 
-	prwe, err := NewPRWExporter(prwCfg, params.BuildInfo)
+	prwe, err := NewPRWExporter(prwCfg, params.BuildInfo, params.Logger)
 	if err != nil {
 		return nil, err
 	}