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Testing and Deploying your Application

Region ID

The REGION_ID is an abbreviated code that Google assigns based on the region you select when you create your app. The code does not correspond to a country or province, even though some region IDs may appear similar to commonly used country and province codes. Including REGION_ID.r in App Engine URLs is optional for existing apps and will soon be required for all new apps.

To ensure a smooth transition, we are slowly updating App Engine to use region IDs. If we haven't updated your Google Cloud project yet, you won't see a region ID for your app. Since the ID is optional for existing apps, you don't need to update URLs or make other changes once the region ID is available for your existing apps.

Learn more about region IDs.

Learn how to run your application locally, deploy it, and test on App Engine.

Running locally

To test your application's functionality before deploying, run your application in your local environment with the development tools that you usually use. For example, the go run command.

Before deploying your application

Before you can deploy your application:

Deploying your application

Deploy your application to App Engine using the gcloud app deploy command.

During deployment, the Cloud Build service builds a container image of your application to run in the App Engine standard environment. Learn more in Managing build images.

To programmatically deploy your apps, use the Admin API.

Deploying a service

You deploy your application to App Engine by deploying versions of your application's services and each of their configuration files.

To deploy a version of your application's service, run the following command from the directory where the app.yaml file of your service is located:

gcloud app deploy

Specifying no files with the command deploys only the app.yaml file in your current directory. By default, the deploy command generates a unique ID for the version that you deploy, deploys the version to the Google Cloud project you configured the gcloud command-line tool to use, and routes all traffic to the new version.

You can change the default behavior of the command by targeting specific files or including additional parameters:

  • To deploy the other configuration files of your service, you must target and deploy each file separately. For example:
    gcloud app deploy cron.yaml
    gcloud app deploy dispatch.yaml
    gcloud app deploy index.yaml
  • To specify a custom version ID, use the --version flag.
  • To prevent traffic from being automatically routed to the new version, use the --no-promote flag.
  • To deploy to a specific Google Cloud project, use the --project flag.

For example, to deploy the service defined by the app.yaml file to a specific Google Cloud project, assign it a custom version ID, and prevent traffic from being routed to the new version:

gcloud app deploy --project PROJECT_ID --version VERSION_ID --no-promote

For more information about this command, see the gcloud app deploy reference.

Deploying multiple services

You use the same deployment command for deploying or updating the multiple services that make up your application.

To deploy multiple services, separately deploy each service's app.yaml file. You can specify multiple files with a single gcloud app deploy command:

gcloud app deploy service1/app.yaml service2/app.yaml

Requirements for deploying multiple services

  • You must initially deploy a version of your application to the default service before you can create and deploy subsequent services.
  • The ID of each of your services must be specified in their corresponding app.yaml configuration files. To specify the service ID, include the service element definition in each configuration file. By default, excluding this element definition from your configuration file deploys the version to the default service.

Ignoring files

You can use a .gcloudignore file to specify files and directories that will not be uploaded to App Engine when you deploy your services. This is useful for ignoring build artifacts and other files that do not need to be uploaded with your deployment.

Managing build images

Each time you deploy a new version, a container image is created using the Cloud Build service. That container image then runs in the App Engine standard environment.

Built container images are stored in the app-engine-tmp/app folder in Container Registry. You can download these images to keep or run elsewhere. Once deployment is complete, App Engine no longer needs the container images. Note that they are not automatically deleted, so to avoid reaching your storage quota, you can safely delete any images you don't need. For more information about managing images in Container Registry, see the Container Registry documentation.

Viewing your application

After you deploy your application to App Engine, you can run the following command to launch your browser and view it at https://PROJECT_ID.REGION_ID.r.appspot.com:

gcloud app browse

Testing on App Engine before shifting traffic

Before configuring a new version to receive traffic, you can test it on App Engine. For example, to test a new version of your default service:

  1. Deploy your new version, but prevent traffic from being automatically routed to the new version:

    gcloud app deploy --no-promote

  2. Access your new version by navigating to the following URL:


    Now you can test your new version in the App Engine runtime environment. You can debug your application by viewing its logs. For more information, see Writing Application Logs.

    App Engine routes requests sent to https://PROJECT_ID.REGION_ID.r.appspot.com to the version previously configured to receive traffic.

  3. When you want to send traffic to the new version, use the Cloud Console to migrate traffic:

    Manage versions

    Select the version you just deployed and click Migrate traffic.

You can use the same process to test new versions of other services by replacing default in the URL with your service's name:


For more information about targeting specific services and versions, see How Requests are Routed.

Using build environment variables

You can also set build environment variables for runtimes that support buildpacks.

Build environment variables are key/value pairs deployed alongside an app that let you pass configuration information to buildpacks. For example, you might want to customize compiler options. You can add or remove these build environment variables by configuring the build_env_variables field in your app.yaml file.