Fix/prometheusexporter Shutdown HTTP server (#35465)

**Description:** Shutdown the http.Server instance on exporter shutdown

**Link to tracking Issue:** #35464 

**Testing:** Manual testing. I included this version of the exporter in
our internal distribution and deployed it to verify the metrics no
longer go stale after receiving a `NOHUP` signal.

**Documentation:** n/a

---------

Co-authored-by: David Ashpole <[email protected]>

.chloggen/fix_prometheusexporter-shutdown-server.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: prometheusexporter
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: "Fixes an issue where the prometheus exporter would not shut down the server when the collector was stopped."
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [35464]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

exporter/prometheusexporter/prometheus.go

@@ -20,7 +20,7 @@ type prometheusExporter struct {
 	config       Config
 	name         string
 	endpoint     string
-	shutdownFunc func() error
+	shutdownFunc func(ctx context.Context) error
 	handler      http.Handler
 	collector    *collector
 	registry     *prometheus.Registry
@@ -44,7 +44,7 @@ func newPrometheusExporter(config *Config, set exporter.Settings) (*prometheusEx
 		endpoint:     addr,
 		collector:    collector,
 		registry:     registry,
-		shutdownFunc: func() error { return nil },
+		shutdownFunc: func(_ context.Context) error { return nil },
 		handler: promhttp.HandlerFor(
 			registry,
 			promhttp.HandlerOpts{
@@ -63,11 +63,17 @@ func (pe *prometheusExporter) Start(ctx context.Context, host component.Host) er
 		return err
 	}
 
-	pe.shutdownFunc = ln.Close
-
 	mux := http.NewServeMux()
 	mux.Handle("/metrics", pe.handler)
 	srv, err := pe.config.ToServer(ctx, host, pe.settings, mux)
+	pe.shutdownFunc = func(ctx context.Context) error {
+		errLn := ln.Close()
+		if srv == nil {
+			return errLn
+		}
+		errSrv := srv.Shutdown(ctx)
+		return errors.Join(errLn, errSrv)
+	}
 	if err != nil {
 		return err
 	}
@@ -88,6 +94,6 @@ func (pe *prometheusExporter) ConsumeMetrics(_ context.Context, md pmetric.Metri
 	return nil
 }
 
-func (pe *prometheusExporter) Shutdown(context.Context) error {
-	return pe.shutdownFunc()
+func (pe *prometheusExporter) Shutdown(ctx context.Context) error {
+	return pe.shutdownFunc(ctx)
 }

exporter/prometheusexporter/prometheus_test.go

@@ -135,11 +135,6 @@ func TestPrometheusExporter_WithTLS(t *testing.T) {
 
 	t.Cleanup(func() {
 		require.NoError(t, exp.Shutdown(context.Background()))
-		// trigger a get so that the server cleans up our keepalive socket
-		var resp *http.Response
-		resp, err = httpClient.Get("https://localhost:7777/metrics")
-		require.NoError(t, err)
-		require.NoError(t, resp.Body.Close())
 	})
 
 	assert.NotNil(t, exp)
@@ -196,11 +191,6 @@ func TestPrometheusExporter_endToEndMultipleTargets(t *testing.T) {
 
 	t.Cleanup(func() {
 		require.NoError(t, exp.Shutdown(context.Background()))
-		// trigger a get so that the server cleans up our keepalive socket
-		var resp *http.Response
-		resp, err = http.Get("http://localhost:7777/metrics")
-		require.NoError(t, err)
-		require.NoError(t, resp.Body.Close())
 	})
 
 	assert.NotNil(t, exp)
@@ -280,11 +270,6 @@ func TestPrometheusExporter_endToEnd(t *testing.T) {
 
 	t.Cleanup(func() {
 		require.NoError(t, exp.Shutdown(context.Background()))
-		// trigger a get so that the server cleans up our keepalive socket
-		var resp *http.Response
-		resp, err = http.Get("http://localhost:7777/metrics")
-		require.NoError(t, err)
-		require.NoError(t, resp.Body.Close())
 	})
 
 	assert.NotNil(t, exp)
@@ -359,11 +344,6 @@ func TestPrometheusExporter_endToEndWithTimestamps(t *testing.T) {
 
 	t.Cleanup(func() {
 		require.NoError(t, exp.Shutdown(context.Background()))
-		// trigger a get so that the server cleans up our keepalive socket
-		var resp *http.Response
-		resp, err = http.Get("http://localhost:7777/metrics")
-		require.NoError(t, err)
-		require.NoError(t, resp.Body.Close())
 	})
 
 	assert.NotNil(t, exp)
@@ -441,11 +421,6 @@ func TestPrometheusExporter_endToEndWithResource(t *testing.T) {
 
 	t.Cleanup(func() {
 		require.NoError(t, exp.Shutdown(context.Background()))
-		// trigger a get so that the server cleans up our keepalive socket
-		var resp *http.Response
-		resp, err = http.Get("http://localhost:7777/metrics")
-		require.NoError(t, err, "Failed to perform a scrape")
-		require.NoError(t, resp.Body.Close())
 	})
 
 	assert.NotNil(t, exp)