Deploying a Java App

Deploy your app to upload and run it on App Engine. When you deploy your apps, you create versions of those apps and their corresponding services in App Engine. You can deploy entire apps, including all the source code and configuration files, or you can deploy and update individual versions or configuration files.

To programmatically deploy your apps, use the Admin API.

Before you begin

Before you can deploy your app:

  • The Owner of the Cloud project must create the App Engine application.

  • Ensure that your user account includes the required privileges.

  • Give Cloud Build permission to deploy apps in your project. When you deploy your app, App Engine uses Cloud Build to build the app into a container and deploy the container to the runtime. Cloud Build does not have permission to deploy Java 8 apps by default, so you need to give permission before you can deploy apps.

To deploy your app using the Maven build tool, you must set up your project to use the Maven plugin for App Engine.

Installing the gcloud command line tool

To deploy your app with the gcloud tool, you must download, install, and initialize the Cloud SDK.

Download the SDK

If you already have the gcloud tool installed and want to configure it to use a Cloud project ID other than the one that you initialized it to, see Managing Cloud SDK Configurations.

Using a proxy

If you are running the deployment command from a system which uses an HTTP or HTTPS proxy, you must configure the tool so that it can communicate via the proxy.

Run the following commands to configure the gcloud tool:

gcloud config set proxy/type [PROXY_TYPE]
gcloud config set proxy/address [PROXY_ADDRESS]
gcloud config set proxy/port [PROXY_PORT]

You can also set a username and password for the proxy. For more information, see gcloud config.

Deploying an app

To deploy your app to App Engine, use either the Maven build tool (recommended) or the gcloud app deploy command from within the root directory of your application.

To deploy your app with the Maven build tool, run the following command from your project's top level directory, where the pom.xml file is located:

mvn package appengine:deploy -Dapp.deploy.projectId=PROJECT_ID

Replace PROJECT_ID with the ID of your Cloud project. If your pom.xml file already specifies your project ID, you don't need to include the -Dapp.deploy.projectId property in the command you run.

Using gcloud command line

  gcloud app deploy [CONFIGURATION_FILES]

Replace [CONFIGURATION_FILES] with the path to one or more configuration files. Use a single white space to separate pathnames.

Optional flags:

  • --version: Specifies a custom version ID. If you don't specify a version ID, App Engine generates one.
  • --no-promote: Deploys your app without automatically routing all traffic to that version. By default, each version that you deploy is automatically configured to receive 100% of traffic.
  • --project: Specifies an alternate Cloud project ID to what you initialized as the default in the gcloud tool.

For more information, see the gcloud app deployreference or run gcloud help from the command line.

Choosing unique version IDs

For manually-scaled instances, the ID of your version should begin with a letter to distinguish them from numeric instance IDs. This ensures that requests are routed to the correct destination and avoids the ambiguity with URL patterns like 123-dot-my-service.[REGION_ID], which can be interpreted two ways:

  • If version 123 exists, the request is routed to version 123 of the my-service service.
  • If version 123 does not exist, the request is instead routed to instance ID 123 where the versions of the my-service service are running.

You can name your versions however you like for instances that are configured for auto scaling or basic scaling because targeting those instances is not supported.

Deploying multiple service applications

When your application is factored into multiple services, you can deploy and update individually targeted services or all the services simultaneously. Deploying updates to services can include updating individual configuration files or updating the source code in the corresponding versions.

For example, you can deploy and create two versions in App Engine, where each version runs in their own service. The first version serves as the frontend service and the other as the backend of your app. You can then deploy individual configuration files to update only the settings of a service. You can also choose to deploy a new version to a service in order to update the source code of the frontend, backend, or both simultaneously.

Requirements for multiple services

You use the same deployment commands for deploying and updating the multiple services of your application with the following requirements:

  • You must initially deploy a version of your app to the default service before you can create and deploy subsequent services.

  • You must specify the ID of your service in the appengine-web.xml configuration file of the corresponding version. To specify the service ID, you include the module: [YOUR_SERVICE_ID] element definition in each configuration file. By default, excluding this element definition from your configuration file deploys the version to the default service.

  • You must specify all the corresponding appengine-web.xml configuration files in your deployment command to simultaneously deploy multiple services. The default service must be listed first.

To deploy multiple services

From the root directory of the application where the configuration files are located, you run the deployment command and specify the relative paths and file names for each service's appengine-web.xml file.

Using the Maven build tool

If the root directory of your project contains only your services, you can deploy all those services with a single Maven command.

The Maven deployment command iterates through each of your project’s services to locate their configuration files and then deploy each service.

To deploy multiple services using the Maven plugin:

  1. Ensure that appengine-maven-plugin has been added to your parent pom.xml file.
  2. Run the following command:

    mvn package appengine:deploy -Dapp.deploy.projectId=PROJECT_ID

    Replace PROJECT_ID with the ID of your Cloud project. If your pom.xml file already specifies your project ID, you don't need to include the -Dapp.deploy.projectId property in the command you run.

Using gcloud

    gcloud app deploy [CONFIGURATION_FILES]

Replace [CONFIGURATION_FILES] with the path to one or more configuration files. Use a single white space to separate pathnames.

You will receive verification via the command line as each service is successfully deployed.

Updating indexes

To create or update the indexes that your apps use, upload the datastore-indexes.xml configuration file to Datastore. Indexes that don't exist yet are created after that configuration file is uploaded.

It can take a while for Datastore to create all the indexes and therefore, those indexes won't be immediately available to App Engine. If your app is already configured to receive traffic, then exceptions can occur for queries that require an index which is still in the process of being built.

To avoid exceptions, you must allow time for all the indexes to build, for example:

For more information about indexes, see Configuring Datastore Indexes.


The following are common error messages that you might encounter:

PERMISSION_DENIED: Operation not allowed
The "appengine.applications.create" permission is required.
If the Cloud project does not include the required App Engine application, the gcloud app deploy command can fail when it tries to run the gcloud app create command. Only accounts with Owner role have the necessary permissions to create App Engine applications.
Command not found
If you did not create symlinks for the tools when you installed the (deprecated) App Engine SDK, you might need to specify the full directory path to run the tool, for example: [PATH_TO_APP_ENGINE_SDK]/ .
Import Error
If you installed both the Cloud SDK as well as the original App Engine SDK, the entries to your PATH might conflict with one another and cause import errors. If you received errors when running Cloud SDK commands, try explicitly using the original App Engine SDK. You can move the entry for the original App Engine SDK to earlier in your PATH so that those commands have priority. Alternatively, you can run the command by specifying the full directory path: [PATH_TO_APP_ENGINE_SDK]/
[400] The first service (module) you upload to a new application must be the 'default' service (module)
Before you can deploy and create the multiple services of your application, you must first deploy and create the default service. For details about how to deploy a version to the default service, see Deploying multiple service applications.
Too Many Versions (403)
App Engine has a limit on the number of deployed versions of your application. These differ for free applications and deployed applications. You can use the Cloud Console to delete an older version and then upload your latest code. You do not have permission to modify this app (403)
This can occur when the account that you are authenticated as does not have permission to deploy to the application ID that is specified in your command or in your appengine-web.xml. Check your application ID is accurate and matches the value of your Cloud Console project ID. Next, check the project permissions in the console and verify that your account is listed with a sufficient permission level to allow for deploying apps.
Other deployment error
If your deployment fails, make sure the Cloud Build API is enabled in your project. App Engine enables this API automatically the first time you deploy an app, but if someone has since disabled the API, deployments will fail.

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