In case you have both domains in App Engine, you can route from one service to another using dispatch.yaml. In the documentation there is an example, as it is stated there:
The following is a sample dispatch file that routes requests to
http://simple-sample.appspot.com
and requests like
http://simple-sample.appspot.com/favicon.ico
to the default service.
All static content is served from the default service. Mobile requests
like http://simple-sample.appspot.com/mobile/
are routed to a mobile
frontend, and worker requests like
http://simple-sample.appspot.com/work/
are routed to a static backend.
And here's the configuration:
dispatch:
# Default service serves the typical web resources and all static resources.
- url: "*/favicon.ico"
service: default
# Default service serves simple hostname request.
- url: "simple-sample.appspot.com/"
service: default
# Send all mobile traffic to the mobile frontend.
- url: "*/mobile/*"
service: mobile-frontend
# Send all work to the one static backend.
- url: "*/work/*"
service: static-backend
There are more possible configurations and description of the syntax in the documentation. Also it is important not to forget to deploy with:
gcloud app deploy dispatch.yaml