Provide scraping target different from FQDN

Signed-off-by: Matteo Castellini <matteo.castellini@buildo.io>

Author: mcastellini

cmd/client/main.go

@@ -49,6 +49,7 @@ var (
 	tlsCert     = kingpin.Flag("tls.cert", "<cert> Client certificate file").String()
 	tlsKey      = kingpin.Flag("tls.key", "<key> Private key file").String()
 	metricsAddr = kingpin.Flag("metrics-addr", "Serve Prometheus metrics at this address").Default(":9369").String()
+	target      = kingpin.Flag("target", "Scraping target").String()
 
 	retryInitialWait = kingpin.Flag("proxy.retry.initial-wait", "Amount of time to wait after proxy failure").Default("1s").Duration()
 	retryMaxWait     = kingpin.Flag("proxy.retry.max-wait", "Maximum amount of time to wait between proxy poll retries").Default("5s").Duration()
@@ -133,6 +134,14 @@ func (c *Coordinator) doScrape(request *http.Request, client *http.Client) {
 		return
 	}
 
+	if *target != "" {
+		if request.URL.Port() == "" {
+			request.URL.Host = *target
+		} else {
+			request.URL.Host = *target + ":" + request.URL.Port()
+		}
+	}
+
 	scrapeResp, err := client.Do(request)
 	if err != nil {
 		msg := fmt.Sprintf("failed to scrape %s", request.URL.String())
@@ -280,6 +289,10 @@ func main() {
 		}()
 	}
 
+	if *target != "" {
+		level.Info(coordinator.logger).Log("msg", "Scraping target", "target", *target)
+	}
+
 	transport := &http.Transport{
 		Proxy: http.ProxyFromEnvironment,
 		DialContext: (&net.Dialer{