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Comment by shykes | Hacker News Reader

Hi, Docker author. Just wanted to say that we are aware of the problem, understand the underlying mechanics, and plan to fix it. In the meantime application-level fixes like this can definitely help.

One slight difficulty is that some applications do want to be pid1. While 99% of the ecosystem wants the problem of being pid1 to be handled natively by Docker, the remaining 1% (people who write init systems, or platforms tied to a particular init system) emphatically wants the opposite. So we need to make sure both modes of operations are available, and deal with a dilemma: do we change the default behavior, potentially breaking images expecting to be run as pid1? Or do we keep a default which breaks 99% of applications, requiring an explicit setting to opt into the correct behavior?

Anybody with opinions on the matter is welcome to voice them on #docker-dev / freenode, or the dev mailing list, we'd love to hear from you.

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Having a config option is a good idea. I vote for changing the default behavior because Docker has so much growth potential left. Leaving the default as-is is problematic for the majority of people, both current and future. I think that breaking it is acceptable because a lot of the people who use Docker in production -- especially those that are expecting to be PID 1 -- are early adopters and will forgive you for the slight breakage.

Yes, change it now, before it's everywhere. The longer you wait, the worse the problem becomes.

As long as you provide a choice on what to run as PID1, and that init system immediately/automatically runs the ENTRYPOINT / CMD / run command I think it is fine to change the behaviour to the correct one. Please don't make the mistake to hardcode PID1, and worst of all not to systemd ... as systemd causes enough trouble in docker containers already (try debian host, fedora:20 docker and upgrade if you can).

Don't worry, we believe in small composable tools, for example we are planning to break up Docker into more discrete binaries. So we're not about to bundle systemd into every Docker installation ;)

Are there any progressing issues we can follow?

I think phusion's base images solution is overkill (its own init written in python3 and force users to use runit). It will be great if I can use systemd inside container (I am a CentOS 7 user, use systemd is quite easy for most packages e.g.: yum install httpd; systemctl start httpd), but it requires --privileged. Now I am considering s6 as solution based on this article: http://blog.tutum.co/2014/12/02/docker-and-s6-my-new-favorit...

But I think it will be the best if docker solve this problem itself, then I can freely use my familiar tools like monit.

How would this then be solved? Letting the .dockerinit process handle this?

And to be honest - the problem is exaggerated and not worth fixing on Docker level. Programs launching child processes have to handle SIGCHLD properly anyway - PID 1 or not. This is only a problem with badly written software.

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