The original App Engine architecture is based on a single frontend instance with optional backend instances. If you have an application that uses backends, you might want to convert the backends to a service format to take full advantage of the additional functionality that services provide, such as the ability to version backends.
App Engine automatically runs an existing backend as a new, non-default version of the default service. Resident backends are assigned manual scaling and dynamic backends are assigned basic scaling.
You can convert backend instances to named services that are versioned and have
explicit scaling type and instance classes. You must replace the original
backends.yaml file with multiple
.yaml files as shown below.
For example, here is a fragment from a
.yaml file that defines three backends
backends: - name: memdb class: B8 instances: 5 - name: worker start: worker.app options: failfast - name: cmdline options: dynamic
To convert these backends to services, create a separate
.yaml file for each
service: memdb version: uno instance_class: B8 manual_scaling: instances: 5
service: worker version: uno # For failfast functionality, please use the ‘X-AppEngine-FailFast’ header on requests made to this service. manual_scaling: instances: 1 handlers: # If a service has an _ah/start handler, it should be listed first. - url: /_ah/start script: worker.app
Note that the original definition of the worker backend used the
start: tag to
bind the script
worker.app to the
_ah/start path. For services, this binding
is defined as a handler with the explicit
_ah/start path. Additionally, if
there's more than one handler, the
_ah/start handler should be listed first.
service: cmdline version: uno basic_scaling: max_instances: 1
The Python SDK contains a script that can perform these transformations for you.
.yaml files, one for the app and one for its backends, it creates
.yaml files defining services for each backend. Using the migration
example above, assume the original file defining the three backends is called
backends.yaml, and the file defining the main app is
app.yaml. The script
would generate three new
cmdline.yaml. Here is how to call it:
[PATH_TO_SDK]/google-cloud-sdk/platform/google_appengine/backends_conversion.py backends.yaml app.yaml