standalone units vs units in peer relationship

[Gustavo Niemeyer]

Hey Stuart,

I'm not quite if it is in the roadmap or not, but a very simple
approach was documented over the past sprint, so there might be a good
chance it gets implemented: http://goo.gl/birTcN


On Mon, Nov 25, 2013 at 8:31 AM, Stuart Bishop
<stuart.bishop at canonical.com> wrote:
> Whenever I deploy a new unit, the 'install' and 'config-changed' hooks
> are run and it configures it self as a standalone unit. If there are
> other units in the service, peer relation-joined and peer
> relation-changed hooks are run and the unit reconfigures itself to be
> a member of this cluster.
>
> The problem I am having is with access to an external resource defined
> by the service's yaml configuration (in my case, a Swift container
> used to store WAL logs for PITR). There is always a period where there
> are two (or more) units that believe they are standalone units and in
> control of the shared resource.
>
> I think I have a work around - use the unit name to generate a unique
> Swift container name and use that until the unit has joined the peer
> relationship. There are a few drawbacks to this approach so it isn't
> ideal.
>
> Can anyone think of a better model for this? I do notice from the logs
> that a standalone unit will join the peer relationship, although no
> peer relation joined hook is run until at least one more unit has
> joined. If the unit joined was joined to the peer relationship right
> at the start, before the initial config-changed hook is run, then it
> could detect that there are other units in the service (but I suspect
> this would still be racy).
>
> I think I recall a helper being suggested to allow a master unit to be
> elected safely which would solve my problem properly (and also remove
> a lot of complexity from my charm). Did anything like this get on the
> roadmap?
>
> --
> Stuart Bishop <stuart.bishop at canonical.com>
>
> --
> Juju mailing list
> Juju at lists.ubuntu.com
> Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/juju

-- 
gustavo @ http://niemeyer.net