Coordinating actions in a service

[Gustavo Niemeyer]

On Fri, May 8, 2015 at 10:24 AM, John Weldon <johnweldon4 at gmail.com> wrote:

> Hi Stuart;
>
> I think this is addressed in the proposed work for Actions 2.0
>
> In the current model you'd have to manage all of this yourself.  Actions
> can only be targeted to specific units in the current implementation, so
> you'd have to manage the distribution outside of actions (or else, as you
> suggest, some sort of generalised semaphore service, and a way to find all
> units of a service and queue up actions for all of them and have the
> actions individually manage themselves whether to run or not)
>
> The plan is to allow actions to be targeted at 1) specific units in a
> service, 2) leaders only, 3) all units in a service, or 4) a subset of
> units in a service.  This would still be a little tricky for your use case,
> but you could at least manage all the logic in an action targeted at only
> the leader for example.
>

None of these seem to fix the issue, though. The requirement is to execute
on all units, but not at the same time. Also, the leader has no way to
communicate with peer units without the hook terminating, right? There
should be a way to postpone the result of an action to a moment past the
end of the hook, but I actually think the proper way to fix this is to
avoid the avalanche in the first place, by default: when dispatching an
action to all units of a service, roll out in a sane way rather than doing
all at once.


gustavo @ http://niemeyer.net
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