Docker-node: Exit on SIGINT

[FranklinYu]

When I use the image with

CMD ["node", "app.js"]

and run my image with docker run -it, it does not reacts to SIGINT fired by Ctrl-C. I think it is because Node.js does not handle SIGINT when running as root process (as discussed in moby/moby#2838). It does not make sense to exit in this case generally, but it does when running in Docker.

[tianon]

Don't you have to specifically create a SIGINT handler, as noted in https://nodejs.org/api/process.html#process_signal_events?

Another alternative would be to use --init on your docker run line to have Docker automatically inject tini to give the default non-pid-1 behavior of SIGINT killing your process if it doesn't have a registered handler.

[FranklinYu]

@tianon If the process is not running as root process, Node.js will catch the SIGINT for you. No need to write anything. I know I can write my own handler or resort to tini, but it would be great if this is the default behavior.

[tianon]

That's not Node.js catching SIGINT, that's the behavior of Linux around PID 1 -- if a non-1 PID doesn't capture a signal, the kernel will automatically kill the process instead. With PID 1, it will not do anything, and instead assumes the process must have a signal handler (because PID 1 is supposed to be an init system, typically).

[FranklinYu]

@tianon Thanks for the info. Nevertheless we can have some sort of entrypoint to catch the signal right? Or is there some policy to keep the image Dockerfile-only?

[tianon]

I can't speak for the image maintainers, but I will point out that what you
describe is exactly what Docker's "--init" flag provides transparently.

[SimenB]

Since kubernetes does not allow you to pass --init (at least it didn't a couple of years ago, might've changed) we use dumb-init as entrypoint in our images at work.

I think not deviating from standard docker practices makes sense here. Thanks for chiming in as always @tianon!

@nodejs/docker happy to reopen if you disagree