From 331c756471dc307575a3446535e4d97d4789e422 Mon Sep 17 00:00:00 2001
From: "Chris S. Kim" <ckim@hashicorp.com>
Date: Thu, 8 Sep 2022 11:02:05 -0400
Subject: [PATCH] Reuse http.DefaultTransport in UIMetricsProxy (#14521)

http.Transport keeps a pool of connections and should be reused when possible. We instantiate a new http.DefaultTransport for every metrics request, making large numbers of concurrent requests inefficiently spin up new connections instead of reusing open ones.
---
 .changelog/14521.txt | 3 +++
 agent/agent.go       | 5 +++--
 agent/http.go        | 4 ++++
 agent/ui_endpoint.go | 1 +
 4 files changed, 11 insertions(+), 2 deletions(-)
 create mode 100644 .changelog/14521.txt

diff --git a/.changelog/14521.txt b/.changelog/14521.txt
new file mode 100644
index 000000000..8dc0de40f
--- /dev/null
+++ b/.changelog/14521.txt
@@ -0,0 +1,3 @@
+```release-note:improvement
+ui: Reuse connections for requests to /v1/internal/ui/metrics-proxy/
+```
diff --git a/agent/agent.go b/agent/agent.go
index b52c480c2..1bcb6c148 100644
--- a/agent/agent.go
+++ b/agent/agent.go
@@ -939,8 +939,9 @@ func (a *Agent) listenHTTP() ([]apiServer, error) {
 			}
 
 			srv := &HTTPHandlers{
-				agent:    a,
-				denylist: NewDenylist(a.config.HTTPBlockEndpoints),
+				agent:          a,
+				denylist:       NewDenylist(a.config.HTTPBlockEndpoints),
+				proxyTransport: http.DefaultTransport,
 			}
 			a.configReloaders = append(a.configReloaders, srv.ReloadConfig)
 			a.httpHandlers = srv
diff --git a/agent/http.go b/agent/http.go
index 98beb6feb..ff7764f0d 100644
--- a/agent/http.go
+++ b/agent/http.go
@@ -81,6 +81,10 @@ type HTTPHandlers struct {
 	configReloaders []ConfigReloader
 	h               http.Handler
 	metricsProxyCfg atomic.Value
+
+	// proxyTransport is used by UIMetricsProxy to keep
+	// a managed pool of connections.
+	proxyTransport http.RoundTripper
 }
 
 // endpoint is a Consul-specific HTTP handler that takes the usual arguments in
diff --git a/agent/ui_endpoint.go b/agent/ui_endpoint.go
index df6f359de..a418a4017 100644
--- a/agent/ui_endpoint.go
+++ b/agent/ui_endpoint.go
@@ -771,6 +771,7 @@ func (s *HTTPHandlers) UIMetricsProxy(resp http.ResponseWriter, req *http.Reques
 		Director: func(r *http.Request) {
 			r.URL = u
 		},
+		Transport: s.proxyTransport,
 		ErrorLog: log.StandardLogger(&hclog.StandardLoggerOptions{
 			InferLevels: true,
 		}),