Disable config switch (#191)

Add a config environment variable to disable the collection of metrics through this extension. Owing to the rules the lambda engine places on extensions, this isn't as simple as "just exit" - you still have to Register as an extension, and ask for at least the shutdown event. Additionally, add a config switch for "extension name" to make a complicated workaround for disabling the opentelemetry collector possible.

Co-authored-by: Pablo Collins <[email protected]>

cmd/splunk-extension-wrapper/splunk-extension-wrapper.go

@@ -33,16 +33,32 @@ import (
 // the correct value is set by the go linker (it's done during build using "ldflags")
 var gitVersion string
 
+const enabledKey = "SPLUNK_EXTENSION_WRAPPER_ENABLED"
+const extensionNameKey = "SPLUNK_EXTENSION_WRAPPER_NAME"
+
+func enabled() bool {
+	s := strings.ToLower(os.Getenv(enabledKey))
+	return s != "0" && s != "false"
+}
+
 func main() {
+	enabled := enabled()
+
 	configuration := config.New()
 
 	initLogging(&configuration)
 
 	ossignal.Watch()
 
-	m := metrics.New()
+	// When we are running "disabled", don't actually try to emit metrics.
+	// A cleaner design for this would use an interface with a stub implementation,
+	// but 3 or 4 nil checks will do for now, since they're all in one file
+	var m *metrics.MetricEmitter = nil
+	if enabled {
+		m = metrics.New()
+	}
 
-	shutdownCondition := registerApiAndStartMainLoop(m, &configuration)
+	shutdownCondition := registerApiAndStartMainLoop(enabled, m, &configuration)
 
 	if shutdownCondition.IsError() {
 		log.SetOutput(os.Stderr)
@@ -51,10 +67,12 @@ func main() {
 	log.Println("shutdown reason:", shutdownCondition.Reason())
 	log.Println("shutdown message:", shutdownCondition.Message())
 
-	m.Shutdown(shutdownCondition)
+	if m != nil {
+		m.Shutdown(shutdownCondition)
+	}
 }
 
-func registerApiAndStartMainLoop(m *metrics.MetricEmitter, configuration *config.Configuration) (sc shutdown.Condition) {
+func registerApiAndStartMainLoop(enabled bool, m *metrics.MetricEmitter, configuration *config.Configuration) (sc shutdown.Condition) {
 	var api *extensionapi.RegisteredApi
 
 	defer func() {
@@ -67,7 +85,7 @@ func registerApiAndStartMainLoop(m *metrics.MetricEmitter, configuration *config
 		}
 	}()
 
-	api, sc = extensionapi.Register(extensionName(), configuration)
+	api, sc = extensionapi.Register(enabled, extensionName(), configuration)
 
 	if sc == nil {
 		sc = mainLoop(api, m, configuration)
@@ -81,13 +99,17 @@ func registerApiAndStartMainLoop(m *metrics.MetricEmitter, configuration *config
 }
 
 func mainLoop(api *extensionapi.RegisteredApi, m *metrics.MetricEmitter, configuration *config.Configuration) (sc shutdown.Condition) {
-	m.SetFunction(api.FunctionName, api.FunctionVersion)
+	if m != nil {
+		m.SetFunction(api.FunctionName, api.FunctionVersion)
+	}
 
 	var event *extensionapi.Event
 	event, sc = api.NextEvent()
 
 	for sc == nil {
-		sc = m.Invoked(event.InvokedFunctionArn, configuration.SplunkFailFast)
+		if m != nil {
+			sc = m.Invoked(event.InvokedFunctionArn, configuration.SplunkFailFast)
+		}
 		if sc == nil {
 			event, sc = api.NextEvent()
 		}
@@ -121,5 +143,9 @@ func initLogging(configuration *config.Configuration) {
 }
 
 func extensionName() string {
-	return path.Base(os.Args[0])
+	name := os.Getenv(extensionNameKey)
+	if name == "" {
+		name = path.Base(os.Args[0])
+	}
+	return name
 }

internal/extensionapi/extensionapi.go

@@ -53,11 +53,17 @@ type RegisteredApi struct {
 	registerResponse
 }
 
-func Register(name string, configuration *config.Configuration) (*RegisteredApi, shutdown.Condition) {
-	log.Println("Registering...")
+func Register(enabled bool, name string, configuration *config.Configuration) (*RegisteredApi, shutdown.Condition) {
+	log.Println("Registering... " + name)
+        // extensions have to at least call Register and Next; they can't actually be "disabled"
+	// so if we are not enabled, at least subscribe to SHUTDOWN
+	events := []string{ shutdownType }
+	if enabled {
+		events = []string{ invokeType, shutdownType }
+	}
 
 	rb, err := json.Marshal(map[string][]string{
-		"events": {invokeType, shutdownType}})
+		"events": events})
 
 	if err != nil {
 		return nil, shutdown.Api(fmt.Sprintf("can't marshall body: %v", err))