Add response_header_timeout

Add ability to set timeout on downstream separate from dial

Fixes #501

cmd/promxy/config.yaml

@@ -60,6 +60,9 @@ promxy:
         # dial_timeout controls how long promxy will wait for a connection to the downstream
         # the default is 200ms.
         dial_timeout: 1s
+        # response_header_timeout controls how long promxy will wait for headers from a downstream
+        # this does not include the time required to read the response body
+        response_header_timeout: 10s
         tls_config:
           insecure_skip_verify: true
 

pkg/servergroup/config.go

@@ -154,8 +154,9 @@ func (c *Config) UnmarshalYAML(unmarshal func(interface{}) error) error {
 
 // HTTPClientConfig extends prometheus' HTTPClientConfig
 type HTTPClientConfig struct {
-	DialTimeout time.Duration                `yaml:"dial_timeout"`
-	HTTPConfig  config_util.HTTPClientConfig `yaml:",inline"`
+	DialTimeout           time.Duration                `yaml:"dial_timeout"`
+	ResponseHeaderTimeout time.Duration                `yaml:"response_header_timeout"`
+	HTTPConfig            config_util.HTTPClientConfig `yaml:",inline"`
 }
 
 // RelativeTimeRangeConfig configures durations relative from "now" to define

pkg/servergroup/servergroup.go

@@ -270,6 +270,7 @@ func (s *ServerGroup) ApplyConfig(cfg *Config) error {
 		// 5 minutes is typically above the maximum sane scrape interval. So we can
 		// use keepalive for all configurations.
 		IdleConnTimeout:       5 * time.Minute,
+		ResponseHeaderTimeout: cfg.HTTPConfig.ResponseHeaderTimeout,
 		DialContext:           (&net.Dialer{Timeout: cfg.HTTPConfig.DialTimeout}).DialContext,
 		ResponseHeaderTimeout: cfg.Timeout,
 	}