support PostExit Hook

[fahedouch]

What is the problem I am trying to solve ?

Looking at the list of supported hooks, we are missing a hooks for configuring custom actions related to the exit lifecycle ( i.e normal exist / killing a container ..)

In nerdctl project, we need a hooks to deal with container deps when the container exit, such as cleaning some state files.

Describe the solution

add new hook PostExit to the hooks list

[AkihiroSuda]

Did you mean "exist" or "exit" ?

[AkihiroSuda]

And how would it be different from poststop hooks?

[fahedouch]

@AkihiroSuda

Did you mean "exist" or "exit" ?

Yes exit

And how would it be different from poststop hooks?

poststop hook is called after the container is deleted but before the delete operation returns.

PostExit should be called after the container exit

[AkihiroSuda]

PostExit should be called after the container exit

How implementable?

[fahedouch]

PostExit should be called after the container exit

How implementable?

did not get your question ? You mean how to introduce a runtime implementation. If yes I believe that we can easily do this in runc for example, but I have to dig into before answering this question.

[AkihiroSuda]

An OCI runtime process disappears on exec(2)-ing the container process, so I'm not sure how this proposal is implementable.

[fahedouch]

@AkihiroSuda would please give me more details about exec(2)-ing the container process or may be link code or article around this. I am looking for an entrypoint to understand what are saying. thanks

[AkihiroSuda]

@AkihiroSuda would please give me more details about exec(2)-ing the container process or may be link code or article around this. I am looking for an entrypoint to understand what are saying. thanks

https://github.com/opencontainers/runc/blob/v1.1.4/docs/terminals.md#detached

In contrast to foreground mode, in detached mode there is no long-running
foreground runc process once the container has started. In fact, there is no
long-running runc process at all.

[fahedouch]

@AkihiroSuda would please give me more details about exec(2)-ing the container process or may be link code or article around this. I am looking for an entrypoint to understand what are saying. thanks

https://github.com/opencontainers/runc/blob/v1.1.4/docs/terminals.md#detached

In contrast to foreground mode, in detached mode there is no long-running
foreground runc process once the container has started. In fact, there is no
long-running runc process at all.

got the point. Do we have a hook mechanism into containerd that may catch container exit ?

[AkihiroSuda]

Do we have a hook mechanism into containerd that may catch container exit ?

Feel free to submit a proposal in the containerd repo.
Maybe we can extend its restart monitor plugin.

[fahedouch]

opened ticket containerd/containerd#8163