You are very correct in your design pattern for testing a new backend. Duplicating live production requests and testing them against your new backend is actually the preferred way of testing before performing a migration. Having an App Engine proxy act like the actual client is also correct for performing your actual tests.
In terms of the actual 502 errors you are seeing, this is an error thrown by the nginx container that is checking the health of your application code. If your application code is too busy to respond to nginx, nginx will deem your application container to be unhealthy and close the instance's connection from App Engine throwing a 502. App Engine will then automatically start a new instance in its place. You can read more into how to code for the cloud and 502 prevention by looking at previous discussions in the Google Cloud Public Issue Tracker <https://issuetracker.google.com/36081250>and Stack Exchange <https://serverfault.com/questions/873497/502-connection-refused-while-connecting-to-upstream-modify-nginx-upstream-on-g> . -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/google-appengine. To view this discussion on the web visit https://groups.google.com/d/msgid/google-appengine/00aa3140-a522-4d6e-b6e7-0ab6502dc05a%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
