Requests are expected to complete within 60s so a websocket connection is probably not sensible.

https://cloud.google.com/appengine/docs/standard/java/how-re...

For handling incoming long-lived connections, you could pair with Fanout [1] (disclosure: founder). Basically the client sees a raw WebSocket, and your backend gets woken up with HTTP requests when things happen.

I haven't seen anything like this for outbound connections though.

[1] https://fanout.io

(Pm on the team) App Engine Standard does not support websockets at the moment.