how to docker run, support Ctrl+C, and not combine stderr

I have a bunch of scripts that I run inside docker containers. They're called by scripts and are not meant to be interactive. The outer scripts are sometimes run in a terminal, and sometimes not (as in CI).

I want to support users killing the scripts using Ctrl+C, so I currently pass -t (--tty). But I discovered that this option combines stdout and stderr. I don't want that.

Is there a way I can support Ctrl+C and still have stderr?

Solution

The best solution I found is tini. Specifically, add the following to the Dockerfile:

ENV TINI_VERSION v0.18.0
ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini /tini
RUN chmod +x /tini
ENTRYPOINT ["/tini", "-g", "--"]

This is taken mostly verbatim from the tini README, and adds the -g, which makes Ctrl+C work more like you would expect.

Now there's no need to use --tty, and no smushing of stdout and stderr.

How does it work?

tini's author does a great job explaining it. But to summarize, docker runs your process as PID 1. PID 1 is normally init, and it has some responsibilities, like handling signals. bash, and most other programs you might run in your container, don't do those things. tini does, and it does such a good job, they added it to docker as --init. The only problem with that flag is that it doesn't add -g, which is important for shell scripts. So I recommend adding it to the Dockerfile manually.