Fix prometheus input creation of transport on every gather

plugins/inputs/prometheus/prometheus.go

@@ -4,7 +4,6 @@ import (
 	"errors"
 	"fmt"
 	"io/ioutil"
-	"net"
 	"net/http"
 	"sync"
 	"time"
@@ -32,6 +31,8 @@ type Prometheus struct {
 	SSLKey string `toml:"ssl_key"`
 	// Use SSL but skip chain & host verification
 	InsecureSkipVerify bool
+
+	client *http.Client
 }
 
 var sampleConfig = `
@@ -65,6 +66,14 @@ var ErrProtocolError = errors.New("prometheus protocol error")
 // Reads stats from all configured servers accumulates stats.
 // Returns one of the errors encountered while gather stats (if any).
 func (p *Prometheus) Gather(acc telegraf.Accumulator) error {
+	if p.client == nil {
+		client, err := p.createHttpClient()
+		if err != nil {
+			return err
+		}
+		p.client = client
+	}
+
 	var wg sync.WaitGroup
 
 	for _, serv := range p.Urls {
@@ -89,29 +98,30 @@ var client = &http.Client{
 	Timeout:   time.Duration(4 * time.Second),
 }
 
+func (p *Prometheus) createHttpClient() (*http.Client, error) {
+	tlsCfg, err := internal.GetTLSConfig(
+		p.SSLCert, p.SSLKey, p.SSLCA, p.InsecureSkipVerify)
+	if err != nil {
+		return nil, err
+	}
+
+	client := &http.Client{
+		Transport: &http.Transport{
+			TLSClientConfig:   tlsCfg,
+			DisableKeepAlives: true,
+		},
+		Timeout: p.ResponseTimeout.Duration,
+	}
+
+	return client, nil
+}
+
 func (p *Prometheus) gatherURL(url string, acc telegraf.Accumulator) error {
 	var req, err = http.NewRequest("GET", url, nil)
 	req.Header.Add("Accept", acceptHeader)
 	var token []byte
 	var resp *http.Response
 
-	tlsCfg, err := internal.GetTLSConfig(
-		p.SSLCert, p.SSLKey, p.SSLCA, p.InsecureSkipVerify)
-	if err != nil {
-		return err
-	}
-
-	var rt http.RoundTripper = &http.Transport{
-		Dial: (&net.Dialer{
-			Timeout:   5 * time.Second,
-			KeepAlive: 30 * time.Second,
-		}).Dial,
-		TLSHandshakeTimeout:   5 * time.Second,
-		TLSClientConfig:       tlsCfg,
-		ResponseHeaderTimeout: p.ResponseTimeout.Duration,
-		DisableKeepAlives:     true,
-	}
-
 	if p.BearerToken != "" {
 		token, err = ioutil.ReadFile(p.BearerToken)
 		if err != nil {
@@ -120,7 +130,7 @@ func (p *Prometheus) gatherURL(url string, acc telegraf.Accumulator) error {
 		req.Header.Set("Authorization", "Bearer "+string(token))
 	}
 
-	resp, err = rt.RoundTrip(req)
+	resp, err = p.client.Do(req)
 	if err != nil {
 		return fmt.Errorf("error making HTTP request to %s: %s", url, err)
 	}