configure hook

Fri Dec 2 06:49:20 UTC 2016

Le 02/12/2016 à 02:53, Boris Rybalkin a écrit :
> Sorry still more questions on hooks.
>
> As I understand configure hooks are executed after services startup:
> https://github.com/snapcore/snapd/blob/3dc67f49c4b6fe3acd5add647ac35a42fbb395d5/overlord/snapstate/snapstate.go#L184
>
> If this is correct (and that is what I see) it completely breaks the
> idea of generating service configs (many tools want absolute paths in
> their configs) with configure hook as it has to be done before the start.
>
> This explains all my issues with keeping generated configs in
> SNAP_COMMON and every time I enable services and they fail I actually
> see configs from previous install :)
>
> Could anyone confirm this?

Hey Boris,

This is correct.

However, I think this forces some best practices on daemons. Remember
that configure hooks can as well be executed while your process is
running. Your process should be able to pick any configuration change
and adapt accordingly.
So, the idea is to choose sane default, not rely on a configure file
until the user chooses so, and diverge from their default (no config
file or no key in the config file means default).

That enables you to easily migrate defaults if you change them, as still
enable people to choose their own configuration without being impacted
by future default (note that ON (default) -> OFF -> ON switch, isn't a
default anymore, it's a user choice.

To illustrate that, I wrote a snap (codelab coming early next year)
where a nodejs app have a default port and title. However, you can via
"snap set" configure another port or title, and those changes are picked
immediatly by the daemon without restarting. Note that I tried to have a
generic configure hook, generating a key=value store, where setting ""
value revert to default and keeping comments, ordering and other
artefacts in your config
https://github.com/ubuntu/snow-on-me-snap/blob/master/meta/hooks/configure
for the config hook
https://github.com/ubuntu/snow-on-me-snap/blob/master/main.js#L71 for
the nodejs webserver picking up new config on the fly.

Hope that helps outlining why this behaviour shouldn't be a problem and
why organizing your code that way is an advantage in the end (hoping you
can act on the tools that requires this).
Didier

>
> On Fri, Nov 18, 2016 at 12:25 AM, Boris Rybalkin <ribalkin at gmail.com
> <mailto:ribalkin at gmail.com>> wrote:
>
>     After reinstalling snapd (2.17.1) and cleaning /var/lib/snapd/
>     issue seems to go away.
>     Thank you very much!
>
>     On Wed, Nov 16, 2016 at 7:20 PM, Boris Rybalkin
>     <ribalkin at gmail.com <mailto:ribalkin at gmail.com>> wrote:
>
>         After upgrading snapd on desktop 16.04 from xenial-proposed
>         now I have this wired message on install:
>
>         Run configure hook of "syncloud-platform"
>         error: cannot perform the following tasks:
>         - Run configure hook of "syncloud-platform" snap if present
>         (cannot snap-exec: cannot find hook "configure" in
>         "syncloud-platform")
>
>         snap --version                        
>         snap    2.17.1
>         snapd   2.17.1
>         series  16
>         ubuntu  16.04
>
>         Has this changed since 2.17?
>
>
>         On 14 Nov 2016 22:44, "Sergio Schvezov"
>         <sergio.schvezov at canonical.com
>         <mailto:sergio.schvezov at canonical.com>> wrote:
>
>             El 14/11/16 a las 18:35, Boris Rybalkin escribió:
>
>                 VM has snapd v2.17, is it possible to install this
>                 version on desktop 16.04/16.10 so I can have it for
>                 integration tests?
>
>
>             It is in xenial-proposed
>             https://launchpad.net/ubuntu/+source/snapd
>             <https://launchpad.net/ubuntu/+source/snapd>
>             If you want the latest and greatest at all times (non
>             production). If you do this, follow the pinning process in
>             https://wiki.ubuntu.com/Testing/EnableProposed
>             <https://wiki.ubuntu.com/Testing/EnableProposed> to pin
>             snapd to xenial-proposed only and not risk getting more
>             (potentially unstable) -proposed software.
>
>                 Also is there any documentation on how to install
>                 snapd on a linux?
>
>
>             These are the installation instructions available for the
>             variety of distros around:
>             http://snapcraft.io/docs/core/install
>             <http://snapcraft.io/docs/core/install>, in case you
>             wonder where I got that link from, it is available as a
>             link on the web front of http://snapcraft.io
>
>             -- 
>             Snapcraft mailing list
>             Snapcraft at lists.snapcraft.io
>             <mailto:Snapcraft at lists.snapcraft.io>
>             Modify settings or unsubscribe at:
>             https://lists.ubuntu.com/mailman/listinfo/snapcraft
>             <https://lists.ubuntu.com/mailman/listinfo/snapcraft>
>
>
>
>
>     -- 
>     Boris Rybalkin
>     ribalkin at gmail.com <mailto:ribalkin at gmail.com>
>
>
>
>
> -- 
> Boris Rybalkin
> ribalkin at gmail.com <mailto:ribalkin at gmail.com>
>
>

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