I think we should make Flink's logs accessible via kubectl logs per default. Firstly, this is the idiomatic way to obtain the logs from a container on Kubernetes. Secondly, especially if something does not work and the container cannot start/stops abruptly, there is no way to log into the container and look for the log.file. This makes debugging the setup quite hard.
I think the best way would be to create the Flink Docker image in such a way that it logs to stdout. In order to allow access to the log file from the web ui, it should also create a log file. One way to achieve this is to add a ConsoleAppender to the respective logging configuration. Another way could be to start the process in the console mode and then to teeing the stdout output into the log file.