[extension/zpages] Add an option to enable expvar (#11964)

#### Description
Add an option to enable expvar, default is `disable`.

#### Link to tracking issue
Resolve #11081

#### Testing
Add a test case to verify the newly added option works.

---------

Signed-off-by: Hong Chen <[email protected]>
Co-authored-by: Yuri Shkuro <[email protected]>
Co-authored-by: Evan Bradley <[email protected]>

Author: 3 people

.chloggen/zpagesextension-add-expvar.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: zpagesextension
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add expvar handler to zpages extension.
+
+# One or more tracking issues or pull requests related to the change
+issues: [11081]
+
+# (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:
+
+# 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: []

extension/zpagesextension/README.md

@@ -27,6 +27,11 @@ The following settings are required:
 zPages. Use localhost:<port> to make it available only locally, or ":<port>" to
 make it available on all network interfaces.
 
+The following settings can be optionally configured:
+
+- `expvar`
+  - `enabled` (default = false): Enable the expvar services. For detail see [ExpvarZ](#expvarz).
+
 Example:
 ```yaml
 extensions:
@@ -78,6 +83,12 @@ They also allow you to quickly examine error samples
 
 Example URL: http://localhost:55679/debug/tracez
 
+### ExpvarZ
+
+The ExpvarZ exposes the useful information about Go runtime, OTel components could leverage [expvar](https://pkg.go.dev/expvar) library to expose their own state.
+
+Example URL: http://localhost:55679/debug/expvarz
+
 ## Warnings
 
 This extension registers a SpanProcessor to record all the spans created inside

extension/zpagesextension/config.go

@@ -13,6 +13,15 @@ import (
 // Config has the configuration for the extension enabling the zPages extension.
 type Config struct {
 	confighttp.ServerConfig `mapstructure:",squash"`
+
+	Expvar ExpvarConfig `mapstructure:"expvar"`
+}
+
+// ExpvarConfig has the configuration for the expvar service.
+type ExpvarConfig struct {
+	// Enabled indicates whether to enable expvar service.
+	// (default = false)
+	Enabled bool `mapstructure:"enabled"`
 }
 
 var _ component.Config = (*Config)(nil)

extension/zpagesextension/zpagesextension.go

@@ -6,6 +6,7 @@ package zpagesextension // import "go.opentelemetry.io/collector/extension/zpage
 import (
 	"context"
 	"errors"
+	"expvar"
 	"net/http"
 	"path"
 
@@ -18,7 +19,8 @@ import (
 )
 
 const (
-	tracezPath = "tracez"
+	tracezPath  = "tracez"
+	expvarzPath = "expvarz"
 )
 
 type zpagesExtension struct {
@@ -56,6 +58,11 @@ func (zpe *zpagesExtension) Start(ctx context.Context, host component.Host) erro
 		zpe.telemetry.Logger.Warn("zPages span processor registration is not available")
 	}
 
+	if zpe.config.Expvar.Enabled {
+		zPagesMux.Handle(path.Join("/debug", expvarzPath), expvar.Handler())
+		zpe.telemetry.Logger.Info("Registered zPages expvar handler")
+	}
+
 	hostZPages, ok := host.(interface {
 		RegisterZPages(mux *http.ServeMux, pathPrefix string)
 	})

extension/zpagesextension/zpagesextension_test.go

@@ -51,7 +51,7 @@ func newZpagesTelemetrySettings() component.TelemetrySettings {
 
 func TestZPagesExtensionUsage(t *testing.T) {
 	cfg := &Config{
-		confighttp.ServerConfig{
+		ServerConfig: confighttp.ServerConfig{
 			Endpoint: testutil.GetAvailableLocalAddress(t),
 		},
 	}
@@ -78,7 +78,7 @@ func TestZPagesExtensionUsage(t *testing.T) {
 
 func TestZPagesExtensionBadAuthExtension(t *testing.T) {
 	cfg := &Config{
-		confighttp.ServerConfig{
+		ServerConfig: confighttp.ServerConfig{
 			Endpoint: "localhost:0",
 			Auth: &confighttp.AuthConfig{
 				Authentication: configauth.Authentication{
@@ -98,7 +98,7 @@ func TestZPagesExtensionPortAlreadyInUse(t *testing.T) {
 	defer ln.Close()
 
 	cfg := &Config{
-		confighttp.ServerConfig{
+		ServerConfig: confighttp.ServerConfig{
 			Endpoint: endpoint,
 		},
 	}
@@ -110,7 +110,7 @@ func TestZPagesExtensionPortAlreadyInUse(t *testing.T) {
 
 func TestZPagesMultipleStarts(t *testing.T) {
 	cfg := &Config{
-		confighttp.ServerConfig{
+		ServerConfig: confighttp.ServerConfig{
 			Endpoint: testutil.GetAvailableLocalAddress(t),
 		},
 	}
@@ -127,7 +127,7 @@ func TestZPagesMultipleStarts(t *testing.T) {
 
 func TestZPagesMultipleShutdowns(t *testing.T) {
 	cfg := &Config{
-		confighttp.ServerConfig{
+		ServerConfig: confighttp.ServerConfig{
 			Endpoint: testutil.GetAvailableLocalAddress(t),
 		},
 	}
@@ -142,7 +142,7 @@ func TestZPagesMultipleShutdowns(t *testing.T) {
 
 func TestZPagesShutdownWithoutStart(t *testing.T) {
 	cfg := &Config{
-		confighttp.ServerConfig{
+		ServerConfig: confighttp.ServerConfig{
 			Endpoint: testutil.GetAvailableLocalAddress(t),
 		},
 	}
@@ -152,3 +152,33 @@ func TestZPagesShutdownWithoutStart(t *testing.T) {
 
 	require.NoError(t, zpagesExt.Shutdown(context.Background()))
 }
+
+func TestZPagesEnableExpvar(t *testing.T) {
+	cfg := &Config{
+		ServerConfig: confighttp.ServerConfig{
+			Endpoint: testutil.GetAvailableLocalAddress(t),
+		},
+		Expvar: ExpvarConfig{
+			Enabled: true,
+		},
+	}
+
+	zpagesExt := newServer(cfg, newZpagesTelemetrySettings())
+	require.NotNil(t, zpagesExt)
+
+	require.NoError(t, zpagesExt.Start(context.Background(), newZPagesHost()))
+	t.Cleanup(func() { require.NoError(t, zpagesExt.Shutdown(context.Background())) })
+
+	// Give a chance for the server goroutine to run.
+	runtime.Gosched()
+
+	_, zpagesPort, err := net.SplitHostPort(cfg.ServerConfig.Endpoint)
+	require.NoError(t, err)
+
+	client := &http.Client{}
+	resp, err := client.Get("http://localhost:" + zpagesPort + "/debug/expvarz")
+	require.NoError(t, err)
+	defer resp.Body.Close()
+
+	require.Equal(t, http.StatusOK, resp.StatusCode)
+}