Optional daemon

[Didier Roche]

Le 27/10/2016 à 16:50, Aaron Ogle a écrit :
> Greetings,
>
> With our Rocket.Chat snap, we're looking to be able to allow someone
> to run an external mongodb instead of the built in one.  As well as
> we'd like to add something like caddy / traefik etc to do ssl
> termination.  But its not a daemon we would want enabled out of the
> box because of the effect on existing users.
>
> So basically looking for a way let the user of a snap enable or
> disable two different daemons in our snap.
>
> Is this possible using anything out of the box?  Or would I have to
> make the command ran in the daemon look at an environment variable /
> file etc. and determine if it should make the daemon just exit?
>
> How have others handled this?  Or allowing users to customize snap
> behaviour?

Hey Aaron,

sounds like a great plan for usability!

I would suggest using configure hooks to proceed that. Hooks are just a
way for users to set variable=value. Based on that, you can control your
daemon with a configure script (triggered by this command) inside your
snap. This one can triggers start and stop inside a mongodb daemon
wrapper (waiting for a certain value to be passed for instance before
executing the real daemon).

The documentation is not yet published on snapcraft.io AFAIK, but is
available there:
https://github.com/snapcore/snapd/blob/master/docs/hooks.md.

However, please keep in mind about this bug
https://bugs.launchpad.net/snappy/+bug/1636931, we need a new core image
to have snapctl available from your snap, and so, you won't be able to
experiment it right away.

I'll probably write a codelab on this precise topic in a couple of weeks
FYI (once the feature is really available to users and developers).
Cheers,
Didier