Upgrading to the App Engine Flexible Environment Latest Release

This page is for developers using the flexible environment with the setting vm:true in their appengine-web.xml and want to upgrade to the latest release, which requires changes in your app configuration.

This page does not apply to upgrading from the App Engine standard environment, which is covered in Migrating Services from the Standard Environment to the Flexible Environment.

Beta shutdown schedule

You must upgrade your apps before the beta-related services are shut down according to the follow schedule:

Important dates
  • Beta deprecation date: November 15th, 2016

    On November 15th, 2016, all deployments to App Engine using the beta vm:true configuration were deprecated.

  • General availability date: March 10th, 2017

    The App Engine flexible environment (env:flex) was released for general availability on March 10th, 2017.

  • Beta decommission date: December 15th, 2017

    On December 15th, 2017, the Managed VMs environment (vm:true) will be shut down and all apps using the beta vm:true configuration will stop receiving traffic.

Upgrading to the flexible environment

To upgrade to the flexible environment:

  1. Replace your appengine-web.xml file with the app.yaml configuration file, following the tabs provided under Converting from appengine-web.xml to app.yaml. Make sure it contains the following settings:

    runtime: java
    env: flex

  2. Review the breaking changes list to determine whether any additional changes are required in your app.yaml.
  3. If you are using a runtime compatible with the App Engine standard APIs, such as java-compat , see also Continuing to use compat runtimes.
  4. During the upgrade, consider making changes to use new features.
  5. After making the necessary changes, deploy the new version of your app to App Engine.

Converting from appengine-web.xml to app.yaml

If you use a compat runtime and are converting to a flexible runtime, you need to replace your appengine-web.xml configuration with app.yaml. Use the following tabs as a guide:

Java app.yaml

The following shows an app.yaml file for a Java flexible environment app:

runtime: java
env: flex
- url: /.*
  script: this field is required, but ignored
runtime_config:  # Optional
  jdk: openjdk8
  server: jetty9
  instances: 1
  enable_app_engine_apis: true

The following shows an appengine-web.xml file for a Java compat app:

<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
      <setting name="enable_app_engine_apis" value="true"/>

Continuing to use compat runtimes

You must move from the env:vmto env:flex configuration file setting before December 15, 2017. However, you can continue to use a runtime in the flexible environment that is compatible with the App Engine standard APIs, such as java-compat.

To run an application on a compat runtime using the env:flex setting:

  1. Fill out this form.
  2. After you receive a confirmation email, update your app.yaml configuration file as follows:
    1. Replace the deprecated vm:true entry with the env:flex element:
    2. Add the enable_app_engine_apis: true under the beta_settings section:
      • For app.yaml:
          enable_app_engine_apis: true
      • For appengine-web.xml:
            <setting name="enable_app_engine_apis" value="true"/>
  3. To keep your app running using a compat runtime, see the following sections.
  4. Plan the rest of your app's upgrade or migration to env:flex.


If you are using a compat runtime, you cannot use the Blobstore API in the flexible environment to serve blobs. As an alternative, use Cloud Storage. Use the Google Cloud client libraries to store and retrieve data in Cloud Storage.

For more information, see Using Cloud Storage.

Cron service

If you are using a compat runtime, to keep existing handlers working with the Cron service, take the following steps:

  1. Remove security-constraint from the related handler in your web.xml file.
  2. Update the handler to verify that requests originate from App Engine's cron service, X-AppEngine-Cron. Verify that the request originates from IP address `` as detailed in Securing URLs for cron.

Mail service

If you are using a compat runtime, you can use the Mail API to send emails, but you cannot receive emails.

Instead, use a third-party mail provider such as SendGrid, Mailjet, or Mailgun. All of these services offer APIs to send email from applications running anywhere.

For more information on setting up your app to send email, see the following guides:

Task queues service

Although it is unsupported in the flexible environment, if you are approved to use a compat runtime, the App Engine Task Queue API is still available. To keep existing handlers working with the Task Queues service, take the following steps:

  1. Remove security-constraint from the related handler in your web.xml file.
  2. Update the handler to verify that requests originate from App Engine's task queue service:
    • X-AppEngine-QueueName
    • X-AppEngine-TaskName
    • X-AppEngine-TaskRetryCount
    • X-AppEngine-TaskRetryReason
    • X-AppEngine-TaskExecutionCount
    • X-AppEngine-TaskETA

For alternatives to the Task Queue API, see Task queues.

Deferred tasks

The Deferred Tasks libraries are not available in the App Engine flexible environment.

If you are using a compat runtime and need to use deferred tasks instead of a worker service for Task Queues, complete the following steps:

  1. Create a separate queue and post to that queue.
  2. Use a custom key that specifies which code to execute when the task is delivered.
  3. Write a custom handler to process the request and dispatch the code.

Shared-core machine types

Shared-core machine types, which have less than 1 vCPU, are not supported in the App Engine flexible environment. If you are using shared core machines, when you move to env:flex, you must upgrade your machines to be at least one core. Alternatively, you can move the app to the App Engine standard environment.

Warmup requests

/_ah/warmup requests are not supported in the App Engine flexible environment.

To warm up your app, implement a health check handler that only returns a ready status when the application is warmed up.

For example, you can create a readiness check that returns a ready status after initializing the cache so your app won't receive traffic until it is ready.

Issues with large pages

If you encounter errors when serving large JSP subpages that are included via <jsp:include page="subpage.jsp">, update the code to <%@ include file="subpage.jsp" %>.

Static files

If you are defining static files in the section of app.yaml, then these static files are served from App Engine instances directly, instead of from other App Engine infrastructure. The interface and behavior are identical, but a small amount of CPU and other resources are consumed on App Engine instances when a file is served.

Hidden resources

The underlying resources behind flexible environment deployments (including Cloud Load Balancing, Compute Engine instances, and Managed Instance Groups) are hidden in Google Cloud Platform Console in order to provide a fuller abstraction of an App Engine application and its instances. Individual instances can be viewed and controlled in the GCP Console on the Instances page.

Instances can still be unlocked and reached via SSH for debugging purposes. Instead of using the gcloud compute instances command, use gcloud app instances. You can also initiate SSH connections from the GCP Console Instances page.

Breaking changes

Upgrading to the App Engine flexible environment requires a few changes to your code and configuration files. This section includes deprecations and breaking changes that you must address before deploying your app with the env: flex configuration.

Library deprecations

The following libraries and their related services were deprecated on November 15th, 2016, and are not supported in the flexible environment:

app.yaml changes

Replace the deprecated configuration vm:true in your app.yaml file, with the flexible environment setting env:flex.

Authentication changes

You must also update the app.yaml file to remove or replace the other configuration setting that have been deprecated:

  • Secure handlers
    The secure setting under handlers is now deprecated for the App Engine flexible environment. If you need SSL redirection, you can update your application code and use the X-Forwarded-Proto header to redirect http traffic. You can also use the HTTP Strict Transport Security response header.
  • Login handlers
    The login setting under handlers is now deprecated for the App Engine flexible environment. You should follow the guidance for User service migration.

Environment variable changes

The following environment variables have been removed or renamed. When available, the replacement environment variable has been listed:

Deprecated environment variable New environment variable (where applicable)

Request header changes

The following HTTP request headers have changed:

  • Removed from all requests:

  • Now included with all requests:


Memcache service

The Memcache service is currently not available for the App Engine flexible environment. An alpha version of the memcache service will be available shortly. If you would like to be notified when the service is available, fill out this early access form.

If you need access to a memcache service immediately, you can use the third party memcache service from Redis Labs. To access this service, see Caching Application Data Using Redis Labs Memcache.

You can also use Redis Labs Redis Cloud, a third party fully-managed service. To access this service, see Caching Application Data Using Redis Labs Redis.

Task queues

The Task Queue API has limited availability outside of the standard environment. If you want to use the service outside of the standard environment, you can sign up for the Cloud Tasks alpha.

In many cases where you might use pull queues, such as queuing tasks or messages that will be pulled and processed by separate works, Cloud Pub/Sub is a good alternative that offers similar functionality and delivery guarantees.

URL routing changes

You can no longer route traffic to specific instances for apps that are running in the flexible environment. For example, you cannot direct requests to instance instanceID:


New features to consider when upgrading

Take note of the following improvements that you can take advantage of when upgrading your app:

Pricing changes

The App Engine flexible environment release introduces a new pricing model. Customers who are currently using vm:true will receive one year of raw Compute Engine pricing. To view the new prices for the flexible environment, see Costs for flexible environment instances.

Tip: Spending limits are not supported in the flexible environment. You should consider creating budgets and setting alerts.

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