Allow http keep-alive setting to be overridden in config

config/config.go

@@ -526,6 +526,8 @@ type HTTPClientConfig struct {
 	ProxyURL URL `yaml:"proxy_url,omitempty"`
 	// TLSConfig to use to connect to the targets.
 	TLSConfig TLSConfig `yaml:"tls_config,omitempty"`
+	// If set, override whether to use HTTP KeepAlive - defaults OFF
+	KeepAlive *bool `yaml:"keep_alive,omitempty"`
 
 	// Catches all undefined fields and must be empty after parsing.
 	XXX map[string]interface{} `yaml:",inline"`

util/httputil/client.go

@@ -36,11 +36,15 @@ func NewClientFromConfig(cfg config.HTTPClientConfig) (*http.Client, error) {
 	if err != nil {
 		return nil, err
 	}
+	disableKeepAlives := true // hard-coded default unless overridden in config
+	if cfg.KeepAlive != nil {
+		disableKeepAlives = !*cfg.KeepAlive
+	}
 	// The only timeout we care about is the configured scrape timeout.
 	// It is applied on request. So we leave out any timings here.
 	var rt http.RoundTripper = &http.Transport{
 		Proxy:             http.ProxyURL(cfg.ProxyURL.URL),
-		DisableKeepAlives: true,
+		DisableKeepAlives: disableKeepAlives,
 		TLSClientConfig:   tlsConfig,
 	}