First customer pain point pull request - default-hook

[Matthew Williams]

I'm not attempting to cause trouble here - I just want to make sure I
understand the feature - and what effects it might have.

It sounds like any implementation of the default-hook would need to start
with something like: (pseudo-bash)

if JUJU_HOOK_NAME == "start"
 //run start
else if JUJU_HOOK_NAME == "config-changed"
 //run config-changed
else if JUJU_HOOK_NAME == "stop"
 //run stop
else
  //unknown hook
  exit 1
fi

Any default-hook that deviated from this pattern could find itself being
run multiple times in succession - I wonder if that might be confusing/
unexpected to a charm author?
Gustavo's observation about hooks that the charm might no know about yet
means that the else clause is absolutely required, I wonder if that's
obvious to someone who's new to charming?

Just some thoughts - in principle I love the feature

Matt





On Tue, Aug 19, 2014 at 11:10 PM, Gustavo Niemeyer <gustavo at niemeyer.net>
wrote:

> On Tue, Aug 19, 2014 at 6:58 PM, Matthew Williams
> <matthew.williams at canonical.com> wrote:
> > Something to be mindful of is that we will shortly be implementing a new
> > hook for metering (likely called collect-metrics). This hook differs
> > slightly to the others in that it will be called periodically (e.g. once
> > every hour) with the intention of sending metrics for that unit to the
> state
> > server.
> >
> > I'm not sure it changes any of the details in this feature or the pr -
> but I
> > thought you should be aware of it
>
> Yeah, that's a good point. I'm wonder how reliable the use of
> default-hook will be, as it's supposed to run whenever any given hook
> doesn't exist, so charms using that feature should expect _any_ hook
> to be called there, even those they don't know about, or that don't
> even exist yet. The charms that symlink into a single hook seem to be
> symlinking a few things, not everything. It may well turn out that
> default-hook will lead to brittle charms.
>
>
> gustavo @ http://niemeyer.net
>
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