Configuring your app with app.yaml

An App Engine app is configured using an app.yaml file, that contains CPU, memory, network and disk resources, scaling, and other general settings including environment variables. You can select any new Java 11+ version or use the older Eclipse Jetty 9.3 or Java 8 versions. For Eclipse Jetty 9.3 and Java 8, you can use Maven or Gradle.

About app.yaml files

You can specify the runtime configuration for your Java 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.

The following app.yaml demonstrates how to configure your app for Java versions 8, 11, and 17 and later. Note that you must update your app.yaml file to use the new version. See Java runtime for more information about using the new versions.

version 17 and later 

runtime: java
env: flex
runtime_config:
operating_system: "ubuntu22"
runtime_version: "21"
handlers:
- url: /.*
script: this field is required, but ignored

manual_scaling:
instances: 1

version 11 

runtime: java
env: flex
runtime_config:
operating_system: "ubuntu18"
runtime_version: "11"
handlers:
- url: /.*
script: this field is required, but ignored

manual_scaling:
instances: 1

version 8 

runtime: java
env: flex

handlers:
- url: /.*
  script: this field is required, but ignored

Depending on the complexity of your app's service, you might only need to define a few elements in the corresponding app.yaml file. The following example demonstrates what a simple Java app might require in the flexible environment:

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.flexible.yaml, then you must deploy your app using either:

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

All configuration elements

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

Enabling Java Virtual Machine metrics collection

You can configure App Engine flexible environment for Java to collect common metrics for Java Virtual Machine (JVM) processes. The metrics are collected using the same JVM monitoring plugin that Cloud Monitoring uses. To view the full list of metrics for App Engine, see the Google Cloud metrics guide.

If you want to collect these JVM metrics for your app:

  • appengine.googleapis.com/flex/instance/jvm/gc/count
  • appengine.googleapis.com/flex/instance/jvm/gc/time

you'll need to set the following JMX system properties in the environment variables in your app.yaml and deploy your app.

JAVA_USER_OPTS: "-Djava.rmi.server.hostname=172.17.0.1 -Dcom.sun.management.jmxremote.port=10403 -
Dcom.sun.management.jmxremote.rmi.port=10403 -Dcom.sun.management.jmxremote.local.only=false -
Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false"