App Engine Routing.
Defines routing characteristics specific to App Engine - service, version, and instance.
For more information about services, versions, and instances see An
Overview of App
Engine <https://cloud.google.com/appengine/docs/python/an-overview-of-app-engine>,
Microservices Architecture on Google App
Engine <https://cloud.google.com/appengine/docs/python/microservices-on-app-engine>,
App Engine Standard request
routing <https://cloud.google.com/appengine/docs/standard/python/how-requests-are-routed>,
and App Engine Flex request
routing <https://cloud.google.com/appengine/docs/flexible/python/how-requests-are-routed>.
Using AppEngineRouting
requires
`appengine.applications.get https://cloud.google.com/appengine/docs/admin-api/access-control`_
Google IAM permission for the project and the following scope:
https://www.googleapis.com/auth/cloud-platform
App version. By default, the task is sent to the version which is the default version when the task is attempted. For some queues or tasks which were created using the App Engine Task Queue API, host is not parsable into service, version, and instance. For example, some tasks which were created using the App Engine SDK use a custom domain name; custom domains are not parsed by Cloud Tasks. If host is not parsable, then service, version, and instance are the empty string.
Output only. The host that the task is sent to. The host is
constructed from the domain name of the app associated with
the queue's project ID (for example .appspot.com), and the
service,
version, and
instance.
Tasks which were created using the App Engine SDK might have a
custom domain name. For more information, see How Requests
are Routed
<https://cloud.google.com/appengine/docs/standard/python/how-
requests-are-routed>_.