...when the container has no shell, so docker exec -it
won't work.
identify the Container ID of the problematic container
$ docker stats
find the PID of the app process
(it may not be the main PID; if it were, docker kill
would work)
$ docker container top abcd1234
send SIGQUIT to the app process
$ sudo kill -QUIT 1234567
extract the logs to a file
$ docker logs abcd1234 > dump.txt