From ef94c388dbf3b47d6ccd114cba93116366340688 Mon Sep 17 00:00:00 2001
From: Brett Jones <blockloop@users.noreply.github.com>
Date: Tue, 7 Jan 2020 18:53:03 -0600
Subject: [PATCH] sidecar: allow custom http con pool size fix #1953

---
 CHANGELOG.md            | 1 +
 cmd/thanos/sidecar.go   | 7 ++++++-
 pkg/store/prometheus.go | 7 ++++++-
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 134714a9c69..abc62fa2ca1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ We use *breaking* word for marking changes that are not backward compatible (rel
 
 ### Fixed
 
+- [#1955](https://github.com/thanos-io/thanos/pull/1955) Sidecar: enable command line flag to set http connection pool size `--prometheus.connection-pool-size`
 - [#1919](https://github.com/thanos-io/thanos/issues/1919) Compactor: Fixed potential data loss when uploading older blocks, or upload taking long time while compactor is
 running.
 - [#1937](https://github.com/thanos-io/thanos/pull/1937) Compactor: Improved synchronization of meta JSON files.
diff --git a/cmd/thanos/sidecar.go b/cmd/thanos/sidecar.go
index f6961e9766b..54667ed7c81 100644
--- a/cmd/thanos/sidecar.go
+++ b/cmd/thanos/sidecar.go
@@ -65,6 +65,9 @@ func registerSidecar(m map[string]setupFunc, app *kingpin.Application) {
 	minTime := thanosmodel.TimeOrDuration(cmd.Flag("min-time", "Start of time range limit to serve. Thanos sidecar will serve only metrics, which happened later than this value. Option can be a constant time in RFC3339 format or time duration relative to current time, such as -1d or 2h45m. Valid duration units are ms, s, m, h, d, w, y.").
 		Default("0000-01-01T00:00:00Z"))
 
+	connectionPoolSize := cmd.Flag("prometheus.connection-pool-size", "sets the MaxIdleConnsPerHost and MaxIdleConns when connecting to prometheus").
+		Default("100").Int()
+
 	m[component.Sidecar.String()] = func(g *run.Group, logger log.Logger, reg *prometheus.Registry, tracer opentracing.Tracer, _ bool) error {
 		rl := reloader.New(
 			log.With(logger, "component", "reloader"),
@@ -95,6 +98,7 @@ func registerSidecar(m map[string]setupFunc, app *kingpin.Application) {
 			*ignoreBlockSize,
 			component.Sidecar,
 			*minTime,
+			*connectionPoolSize,
 		)
 	}
 }
@@ -120,6 +124,7 @@ func runSidecar(
 	ignoreBlockSize bool,
 	comp component.Component,
 	limitMinTime thanosmodel.TimeOrDurationValue,
+	connectionPoolSize int,
 ) error {
 	var m = &promMetadata{
 		promURL: promURL,
@@ -244,7 +249,7 @@ func runSidecar(
 
 	{
 		promStore, err := store.NewPrometheusStore(
-			logger, nil, promURL, component.Sidecar, m.Labels, m.Timestamps)
+			logger, nil, promURL, component.Sidecar, m.Labels, m.Timestamps, connectionPoolSize)
 		if err != nil {
 			return errors.Wrap(err, "create Prometheus store")
 		}
diff --git a/pkg/store/prometheus.go b/pkg/store/prometheus.go
index 4012eceb9c8..74f4eace9d7 100644
--- a/pkg/store/prometheus.go
+++ b/pkg/store/prometheus.go
@@ -73,13 +73,18 @@ func NewPrometheusStore(
 	component component.StoreAPI,
 	externalLabels func() labels.Labels,
 	timestamps func() (mint int64, maxt int64),
+	connectionPoolSize int,
 ) (*PrometheusStore, error) {
 	if logger == nil {
 		logger = log.NewNopLogger()
 	}
 	if client == nil {
+		t := http.DefaultTransport.(*http.Transport)
+		t.MaxIdleConnsPerHost = connectionPoolSize
+		t.MaxIdleConns = connectionPoolSize
+
 		client = &http.Client{
-			Transport: tracing.HTTPTripperware(logger, http.DefaultTransport),
+			Transport: tracing.HTTPTripperware(logger, t),
 		}
 	}
 	p := &PrometheusStore{