App engine standard java8 - how to add health check for instances?

[Roman Mašek]

Is it possible to implement a custom health-check for instances in App Engine Standard? I tried to configure liveness-check and readiness-check, but these seem to be supported only in flex environment.

The reason I would like to do this is that recently we ran into following issue several times: because of a bug, one of the instances stopped responding successfully to requests, always returning HTTP status 500. This instance has been then kept alive and accessible for hours, leading to intermittent failures for our customers.

[George (Cloud Platform Support)]

Hello Roman, 

It is not possible to implement custom health checks in App Engine Standard. Still, App Engine sends periodic health check requests to confirm that an instance has been successfully deployed, and to check that a running instance maintains a healthy status. Each health check must be answered within a specified time interval. An instance is unhealthy when it fails to respond to a specified number of consecutive health check requests. This procedure covers normally the situation you describe, and offers chances of providing for faulty instances and avoiding status 500 for hours. You should organize your GAE Standard apps to handle this situation. More details on the "How Instances are Managed" page.