PHP 7.4 is now generally available.

Defining Runtime Settings

A PHP 7 app in App Engine is configured using an app.yaml file, that contains the runtime, handlers, scaling, and other general settings including environment variables.

About app.yaml files

Specify all the runtime configuration for your PHP 7 app, including versions and URLs, in the app.yaml file. This file acts as a deployment descriptor of a specific service version. You must first create the app.yaml file for the default service of your app before you can create and deploy app.yaml files for additional services.

You can specify a unique name for your app.yaml files, but then you must specify the file name with the deployment command as well. For example, if you name your app.yaml file service-name-app.yaml or app.standard.yaml, then you must deploy your app using either:

gcloud app deploy service-name-app.yaml
gcloud app deploy app.standard.yaml
To learn more about structuring multiple services and app.yaml files in your app, see Structuring Web Services.

Generally, your app.yaml file requires only the runtime element for a simple PHP 7 app in the standard environment, for example:

appengine/php72/helloworld/app.yaml 
# Use PHP 7.3 by replacing "php72" below with "php73"
runtime: php72

# Defaults to "serve index.php" and "serve public/index.php". Can be used to
# serve a custom PHP front controller (e.g. "serve backend/index.php") or to
# run a long-running PHP script as a worker process (e.g. "php worker.php").
#
# entrypoint: serve index.php

All configuration elements

For a complete list of all the supported elements in this configuration file, see the app.yaml reference.