When setting the socket-read-timeout on gateways the following error is seen in the logs:
Pool unexpected socket timed out on client connection=Pooled Connection to jeppet:54321: Connection[DESTROYED]). Server unreachable: could not connect after 1 attempts
This is a bug in GemFire 8.x and happens when socket-read-timeout is set and the gateway is idle for the period of time defined with socket-read-timeout. Default socket-read-timeout is 0, meaning no timeout, and it is defined in milliseconds when set.
The fix of this bug is currently planned to be included in GemFire 9.0.