[lxc-users] Container startup hook arguments

[Kees Bos]

On wo, 2017-10-04 at 09:35 -0500, Serge E. Hallyn wrote:
> Quoting Kees Bos (cornelis.bos at gmail.com):
> > 
> > I'm not using it, but do expect the extra args:
> > 
> > while [ {{ '${#@}' }} -gt 3 ] ; do
> >    ...
> >    shift
> > done
> > 
> > It might be that some users will need the last extra argument
> > (stage:
> > pre-start|start|post-stop). This is currently not available in the
> > environment.
> > 
> > I can live without these extra arguments, but will have to update
> > my
> > scripts.
> Ok, but this will hurt then.  I certainly was going to keep the
> extra args, but they would be shifted now.  We can pass along an
> environment variable saying something like LXC_SIMPLE_ARGS=1 or
> something, but your unmodified script won't know to look for
> that so will do the wrong thing.  Any ideas?
> 
> This unfortunately basically means that you are in fact a "user",
> and that makes this seem like at best 3.0  material then, unless
> we can find a good solution.
> 
> Maybe a configuration key 'lxc.hooks.version=2' ?

Yep. Or 'lxc.hook.version=2'. However, that would mean you've got to
support is for quite some time. I don't know if that's worth the
effort. It would also mean that you've got to update (lots?) of
container configs. I'm not sure what would be the most painful way to
go.

It would be nice if you define e.g. LXC_HOOK_STAGE=pre-start in the
environment (which is currently not available). Then it's possible to
use a single script to handle multiple stages (which I don't do, but is
currently possible based on the last argument).

This new environment variable can also be used to prepare scripts for
changing behaviour. Without that, my scripts can be prepared for this
with e.g.:
for lastarg; do true; done
if $lastarg = 'pre-start' ; then old-style ; etc; fi