feat: Simple health check endpoint for webhooks (#823)

* feat: Simple health check endpoint for webhooks

* doc

* doc update

* dock change

* re-run codegen

* fix

docs/webhook-health-check.md

@@ -0,0 +1,33 @@
+# Webhook Health Check
+
+![alpha](assets/alpha.svg)
+
+> v1.0 and after
+
+For `webhook` or `webhook` extended event sources such as `github`, `gitlab`,
+`sns`, `slack`, `Storage GRID` and `stripe`, besides the endpint configured in
+the spec, an endpoint `:${port}/health` will be created by default, this is
+useful for LB or Ingress configuration for the event source, where usually a
+health check endpoint is required.
+
+For example, besides `:12000/example1` and `:13000/example2`, the EventSource
+object below also creates 2 extra endpoints, `:12000/health` and
+`:13000/health`. A HTTP GET request to the health endpoint returns a text `OK`
+with HTTP response code `200`.
+
+```yaml
+apiVersion: argoproj.io/v1alpha1
+kind: EventSource
+metadata:
+  name: webhook
+spec:
+  webhook:
+    example:
+      port: "12000"
+      endpoint: /example1
+      method: POST
+    example-foo:
+      port: "13000"
+      endpoint: /example2
+      method: POST
+```

eventsources/common/webhook/webhook.go

@@ -24,6 +24,7 @@ import (
 	"github.com/gorilla/mux"
 	"go.uber.org/zap"
 
+	"github.com/argoproj/argo-events/common"
 	"github.com/argoproj/argo-events/common/logging"
 	"github.com/argoproj/argo-events/pkg/apis/eventsource/v1alpha1"
 )
@@ -99,14 +100,22 @@ func startServer(router Router, controller *Controller) {
 	handler := controller.ActiveServerHandlers[route.Context.Port]
 
 	routeName := route.Context.Port + route.Context.Endpoint
-
 	r := handler.GetRoute(routeName)
 	if r == nil {
 		r = handler.NewRoute().Name(routeName)
 		r = r.Path(route.Context.Endpoint)
+		r.HandlerFunc(router.HandleRoute)
 	}
 
-	r.HandlerFunc(router.HandleRoute)
+	healthCheckRouteName := route.Context.Port + "/health"
+	healthCheckRoute := handler.GetRoute(healthCheckRouteName)
+	if healthCheckRoute == nil {
+		healthCheckRoute = handler.NewRoute().Name(healthCheckRouteName)
+		healthCheckRoute = healthCheckRoute.Path("/health")
+		healthCheckRoute.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
+			common.SendSuccessResponse(writer, "OK")
+		})
+	}
 
 	Lock.Unlock()
 }