You can use custom runtimes to add additional functionality to a PHP app running in the App Engine flexible environment. To configure a custom runtime, replace the following line in your app.yaml file:

runtime: php

with this line:

runtime: custom

You must also specify a base image by adding a Dockerfile in the same directory that contains the app.yaml file.

Visit the Custom runtimes documentation to learn how to define a Dockerfile in a custom runtime.

Health checking

By default, all programs running in the flexible environment receive health check requests. The base image gcr.io/google_appengine/php responds to the health check request, so you don't have to write your own health check handler. If you're using a different image, you need to disable health checks, or write your own code to handle health check requests.