It looks like your application is not responding to the nginx health checks, and this is causing nginx to throw
502 bad gateway.
I suggest you first follow a
Vapor on App Engine tutorial to get a working Vapor configuration running on App Engine. Once you have Vapor setup and running you can then add your application to the working configuration.
Note that Google Groups is meant for general product discussions and not for technical support. If you require further technical aid with deploying Vapor on App Engine, it is recommended to post your questions on
Stack Overflow using the supported Google Cloud tags.