Google Cloud Platform for Developers

Custom runtimes

One of the main benefits of the App Engine flexible environment is the support for custom runtimes. A custom runtime is essentially a non-standard Docker container running on App Engine. Google maintains a collection of Docker images for the various supported language runtimes. These base images are available at https://console.cloud.google.com/gcr/images/google-appengine/GLOBAL. When a non-custom runtime is used, Google will build the Docker image by extending one of these base images, as defined in the runtime property of the app.yaml configuration file.

In some cases, it is useful to either customize one of these runtimes, or use an entirely separate runtime. This allows developers to tweak the runtime to their liking, ...