Error while deploying python in Google App Engine

Question

I am trying to deploy a python application and I am receiving the following error message:

ERROR: (gcloud.app.deploy) Error Response: [4] Your deployment has failed to become healthy in the allotted time and therefore was rolled back. If you believe this was an error, try adjusting the 'app_start_timeout_sec' setting in the 'readiness_check' section.

My app.yaml is:

runtime: python
runtime_config:
  python_version: 3
env: flex
service: newservice
handlers:
- url: /
  script: hello.py

manual_scaling:
  instances: 1
resources:
  cpu: 1
  memory_gb: 0.5
  disk_size_gb: 10

I believe the problem is related to the yaml file, since I have deployed a sample application previously with no problems (using entrypoint on my yaml), then when I added a new python script and referred to it on the yaml file (using the handlers, to run my message block) I started to get this error.

Edit: after GAEFan's answer my hello has included a handler for readiness_check as:

def post():
    self.response.headers['Content-Type'] = 'application/json'   
    obj = {
      'status': 200, 
    } 
    self.response.out.write(json.dumps(obj))

webapp2.WSGIApplication([
    ('/readiness_check', post())
], debug=True)

Answer 1

Readiness checks are enabled by default. So, you should set up url handlers for them. In this case, GAE is sending a request to /readiness_check , but your app.yaml doesn't have a handler for that url. Try this:

handlers:
- url: /.*
  script: hello.py

And make sure the url returns a 200 or similar response. To customize the readiness checking:

readiness_check:
  path: "/readiness_check"
  check_interval_sec: 5
  timeout_sec: 4
  failure_threshold: 2
  success_threshold: 2
  app_start_timeout_sec: 300

Or:

liveness_check:
  path: "/liveness_check"
  check_interval_sec: 30
  timeout_sec: 4
  failure_threshold: 2
  success_threshold: 2

Details at: https://cloud.google.com/appengine/docs/flexible/custom-runtimes/configuring-your-app-with-app-yaml#legacy_health_checks

Answer 2

You're running in a flexible environment app, the handlers configuration is a standard environment one. You need to use the entrypoint configuration for the flexible environment. From Application startup :

The runtime starts your application using the entrypoint defined in app.yaml . The entrypoint should start a process that responds to HTTP requests on the port defined by the environment variable PORT .

Without it your app is not really working and can't serve the health check requests.

Maybe useful: How to tell if a Google App Engine documentation page applies to the standard or the flexible environment