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For the trivial case a child process would work. But ultimately docker does try to be closer to an init system or maybe screen since you can detach/attach to pr

For the trivial case a child process would work. But ultimately docker does try to be closer to an init system or maybe screen since you can detach/attach to processes. Since reparenting to arbitrary processes is not possible in linux it's also not possible to retain the parent-child relationship for spawned containers. If you want the fork-exec model then docker is indeed the wrong tool for the job.

jchw 7y ago
The thing is, I don't even really like Docker as an init daemon. I have my gripes about Systemd but I see no downsides to not having a long-running daemon for a container engine. Really, whether you need root or not isn't even the most important issue; you can do sudo or suid or whatever with any container engine; Docker just has it be an implicit, unintuitive behavior. I used to use systemd+rkt for simple container setups when I didn't need all of Kubernetes. Never noticed any downsides versus using Docker, but on the flip side, I had far fewer issues with my containers not properly starting at boot.
- paulddraper 7y ago
  I read an article (can't find it now) that said from a previous project the Docker authors concluded they wanted a daemon so they didn't have to do things like file locks, etc. around image management. Don't know if that accounts for the whole reason or not.
  - jchw 7y ago
    Oh yeah, I read that - surrounding the original authors at dotCloud about their experiences trying to do it in multiple processes IIRC. That said, it seems the problem may be somewhat solved at this point.
  - cyphar 7y ago
    The reason boiled down to "it's easier to write a daemon to handle it all". But it's definitely not better than the alternative, nor is the alternative impossible.
  - jhealy 7y ago
    Sounds like it might've been this article? https://jpetazzo.github.io/2017/02/24/from-dotcloud-to-docker/ https://jpetazzo.github.io/2017/02/24/from-dotcloud-to-docke...?

jchw 7y ago

The thing is, I don't even really like Docker as an init daemon. I have my gripes about Systemd but I see no downsides to not having a long-running daemon for a container engine. Really, whether you need root or not isn't even the most important issue; you can do sudo or suid or whatever with any container engine; Docker just has it be an implicit, unintuitive behavior. I used to use systemd+rkt for simple container setups when I didn't need all of Kubernetes. Never noticed any downsides versus using Docker, but on the flip side, I had far fewer issues with my containers not properly starting at boot.

paulddraper 7y ago
I read an article (can't find it now) that said from a previous project the Docker authors concluded they wanted a daemon so they didn't have to do things like file locks, etc. around image management. Don't know if that accounts for the whole reason or not.
- jchw 7y ago
  Oh yeah, I read that - surrounding the original authors at dotCloud about their experiences trying to do it in multiple processes IIRC. That said, it seems the problem may be somewhat solved at this point.
- cyphar 7y ago
  The reason boiled down to "it's easier to write a daemon to handle it all". But it's definitely not better than the alternative, nor is the alternative impossible.
- jhealy 7y ago
  Sounds like it might've been this article? https://jpetazzo.github.io/2017/02/24/from-dotcloud-to-docker/ https://jpetazzo.github.io/2017/02/24/from-dotcloud-to-docke...?