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Communicating between your services

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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. For apps created after February 2020, REGION_ID.r is included in App Engine URLs. For existing apps created before this date, the region ID is optional in the URL.

Learn more about region IDs.

You can use various methods to communicate between your App Engine services or with other services, including Google Cloud services and external applications.

The simplest approach for communicating with your App Engine service is to send targeted HTTP requests, where the URL includes the name or ID of a resource. For example, you can include the ID of a service or version that you want to target, in addition to the corresponding Cloud project ID:


https://VERSION-dot-SERVICE-dot-PROJECT_ID.REGION_ID.r.appspot.com

Note that the combined length of VERSION-dot-SERVICE-dot-PROJECT_ID, where VERSION is the name of your version, SERVICE is the name of your service, and PROJECT_ID is your project ID, cannot be longer than 63 characters and cannot start or end with a hyphen. If the combined length is longer than 63 characters, you might see Error DNS address could not be found.

Learn more about requests in App Engine:

Your App Engine services can also communicate using Pub/Sub, which provides reliable asynchronous many-to-many messaging between processes, including App Engine. These processes can be individual instances of your application, services, or even external applications.

To share data across databases and your App Engine app or some other external application, see Understanding Data and File Storage.

If you use the legacy bundled services, you can also pass requests between services and from services to external endpoints using the URL Fetch API.

Additionally, services in the standard environment that reside within the same Cloud project can also use one of the App Engine APIs for the following tasks:

  • Share a single memcache instance.
  • Collaborate by assigning work between services through Task Queues.

Reserved URL paths

It is not possible to use the following URL paths:

  • Paths ending with /eventlog
  • Paths starting with /_ah/
  • Some paths ending with z