Optional daemon

[Didier Roche]

Le 27/10/2016 à 17:33, Aaron Ogle a écrit :
> Didier:
>
> This sounds like exactly what I wanted!  So once this lands I will be
> able to just use: snapctl get value to get user set information?
Exactly!

>
> Will the snapctl command be available anywhere in the snap or only in
> the hooks?

I guess the main intent is to use them primarily in hooks, but nothing
should prevent it to be available in your other snap daemon as well (as
it's part of the core rootfs).

>
> Also the upgrade hook looks like it could be a thing of beauty. Any
> plans for a downgrade hook?

I don't know about any plan for that, I'll let others answer. I think
you mean a downgrade hook being executed after a snap revert to fetch
back "newer data" that could be lost in the revert process and transfer
back to the older version? Or do you have any other use case in mind?

Didier
>
> On Thu, Oct 27, 2016 at 10:14 AM Didier Roche <didrocks at ubuntu.com
> <mailto:didrocks at ubuntu.com>> wrote:
>
>     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
>     <http://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
>
>
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> -- 
>
> 	
> *Aaron Ogle* Core Developer
>
> aaron.ogle at rocket.chat <mailto:aaron.ogle at rocket.chat>
>
> @aaron.ogle <https://demo.rocket.chat/direct/aaron.ogle>
>
> https://rocket.chat
>
>
>

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