cmd/tipgodoc: implement health checking and enable auto-scaling

Change-Id: I860d0913d051616d7958a88a3c7b11a26ec1d4d6
Reviewed-on: https://go-review.googlesource.com/14661
Reviewed-by: Chris Broadfoot <cbro@golang.org>

cmd/tipgodoc/app.yaml

@@ -3,12 +3,10 @@ runtime: custom
 api_version: go1
 vm: true
 
-manual_scaling:
-  instances: 1
+automatic_scaling:
+  min_num_instances: 1
+  max_num_instances: 2
 
 handlers:
 - url: /.*
   script: _go_app
-
-health_check:
-  enable_health_check: False

cmd/tipgodoc/tip.go

@@ -71,6 +71,10 @@ func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, s, http.StatusInternalServerError)
 		return
 	}
+	if r.URL.Path == "/_ah/health" {
+		fmt.Fprintln(w, "OK")
+		return
+	}
 	proxy.ServeHTTP(w, r)
 }