title: are updated health checks causing App Engine deployment to fail?
body: <p>we updated our google app engine health checks from the legacy version to the new version using and now our deployments are failing. Nothing else on the project has changed. We tested the default settings and then extended checks just in case. </p>
  
  <p>This is the error:
  <code>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.
  </code></p>
  
  <p>This is our app.yaml:</p>
  
  <pre><code>liveness_check:
     check_interval_sec: 120
     timeout_sec: 40
     failure_threshold: 5
     success_threshold: 5
     initial_delay_sec: 500
  
  readiness_check:
    check_interval_sec: 120
    timeout_sec: 40
    failure_threshold: 5
    success_threshold: 5
    app_start_timeout_sec: 1500
  </code></pre>
  
  <p>Unfortunately, no matter the configuration, both the readiness and liveness checks are throwing 404s.</p>
  
  <p>What could be causing the problem? and how can we debug this?
  Is it possible to rollback to the legacy health checks?</p>