fix(inputs.prometheus): Remove duplicate response_timeout option (#15078)

plugins/inputs/prometheus/README.md

@@ -141,6 +141,8 @@ See the [CONFIGURATION.md][CONFIGURATION.md] for more details.
   # timeout = "5s"
 
   ## deprecated in 1.26; use the timeout option
+  ## This option is now used by the HTTP client to set the header response
+  ## timeout, not the overall HTTP timeout.
   # response_timeout = "5s"
 
   ## HTTP Proxy support

plugins/inputs/prometheus/prometheus.go

@@ -74,9 +74,8 @@ type Prometheus struct {
 
 	HTTPHeaders map[string]string `toml:"http_headers"`
 
-	ResponseTimeout      config.Duration `toml:"response_timeout" deprecated:"1.26.0;use 'timeout' instead"`
-	ContentLengthLimit   config.Size     `toml:"content_length_limit"`
-	EnableRequestMetrics bool            `toml:"enable_request_metrics"`
+	ContentLengthLimit   config.Size `toml:"content_length_limit"`
+	EnableRequestMetrics bool        `toml:"enable_request_metrics"`
 
 	MetricVersion int `toml:"metric_version"`
 
@@ -213,15 +212,21 @@ func (p *Prometheus) Init() error {
 	}
 
 	ctx := context.Background()
-	if p.ResponseTimeout != 0 {
-		p.HTTPClientConfig.Timeout = p.ResponseTimeout
-	}
 
 	client, err := p.HTTPClientConfig.CreateClient(ctx, p.Log)
 	if err != nil {
 		return err
 	}
 	p.client = client
+	if p.HTTPClientConfig.ResponseHeaderTimeout != 0 {
+		p.Log.Warn(
+			"Config option response_timeout was set to non-zero value. This option's behavior was " +
+				"changed in Telegraf 1.30.2 and now controls the HTTP client's header timeout and " +
+				"not the Prometheus timeout. Users can ignore this warning if that was the intention. " +
+				"Otherwise, please use the timeout config option for the Prometheus timeout.",
+		)
+	}
+
 	p.headers = map[string]string{
 		"User-Agent": internal.ProductToken(),
 		"Accept":     acceptHeader,
@@ -406,9 +411,6 @@ func (p *Prometheus) gatherURL(u URLAndAddress, acc telegraf.Accumulator) (map[s
 				},
 			},
 		}
-		if p.ResponseTimeout != 0 {
-			uClient.Timeout = time.Duration(p.ResponseTimeout)
-		}
 	} else {
 		if u.URL.Path == "" {
 			u.URL.Path = "/metrics"

plugins/inputs/prometheus/prometheus_test.go

@@ -14,7 +14,6 @@ import (
 	"k8s.io/apimachinery/pkg/fields"
 
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/config"
 	"github.com/influxdata/telegraf/metric"
 	"github.com/influxdata/telegraf/testutil"
 )
@@ -241,10 +240,12 @@ func TestPrometheusGeneratesMetricsSlowEndpoint(t *testing.T) {
 	defer ts.Close()
 
 	p := &Prometheus{
-		Log:             testutil.Logger{},
-		URLs:            []string{ts.URL},
-		URLTag:          "url",
-		ResponseTimeout: config.Duration(time.Second * 5),
+		Log:    testutil.Logger{},
+		URLs:   []string{ts.URL},
+		URLTag: "url",
+		client: &http.Client{
+			Timeout: time.Second * 5,
+		},
 	}
 	err := p.Init()
 	require.NoError(t, err)
@@ -271,10 +272,12 @@ func TestPrometheusGeneratesMetricsSlowEndpointHitTheTimeout(t *testing.T) {
 	defer ts.Close()
 
 	p := &Prometheus{
-		Log:             testutil.Logger{},
-		URLs:            []string{ts.URL},
-		URLTag:          "url",
-		ResponseTimeout: config.Duration(time.Second * 5),
+		Log:    testutil.Logger{},
+		URLs:   []string{ts.URL},
+		URLTag: "url",
+		client: &http.Client{
+			Timeout: time.Second * 5,
+		},
 	}
 	err := p.Init()
 	require.NoError(t, err)

plugins/inputs/prometheus/sample.conf

@@ -124,6 +124,8 @@
   # timeout = "5s"
 
   ## deprecated in 1.26; use the timeout option
+  ## This option is now used by the HTTP client to set the header response
+  ## timeout, not the overall HTTP timeout.
   # response_timeout = "5s"
 
   ## HTTP Proxy support