Juju devel 1.23-beta2 is released

[John Meinel]

I believe the Juju agent itself is running a "renew the lease" every 30s.
It probably wouldn't hurt for the charm to check that it is still the
master periodically if it is going to be running for an hour, since it
might lose connection without otherwise realizing.

John
=:->


On Mon, Mar 30, 2015 at 12:05 PM, Stuart Bishop <stuart.bishop at canonical.com
> wrote:

> On 26 March 2015 at 23:58, Curtis Hovey-Canonical <curtis at canonical.com>
> wrote:
>
> > ### Service Leader Elections
> >
> > Services running in an environment bootstrapped with the
> > "leader-election" feature flag now have access to three new hook tools:
> >
> >     is-leader - returns true only if the executing unit is guaranteed
> >         service leadership for the next 30s
> >     leader-get - as relation-get; accessible only within the service
> >     leader-set - as relation-set; will fail if not executed on leader
> >
> > ...and two new hooks:
> >
> >     leader-elected - runs when the unit takes service leadership
> >     leader-settings-changed - runs when another unit runs leader-set
> >
> > When a unit starts up, it will always run either leader-elected or
> > leader-settings-changed as soon as possible, delaying only doing so only
> > to run the install hook; complete any queued or in-flight operation; or
> > resolve a hook or upgrade error.
>
> Looking forward to this.
>
> Looking at the specifics, I'm interested in how the leader unit
> performs long running operations with the 30s lease. Lets say unit 0
> is the leader, and decides that it is an appropriate time for unit 0
> to run a repair operation that might take a few hours.
>
> As the wording currently stands, no hooks are triggered on the leader
> when the leader calls leader-set. This gives the leader no alternative
> but to perform the long running operation in the same hook, and risk
> another leader being elected and making a conflicting decision.
>
> I think that the leader-settings-changed hook needs to be called
> whenever *any* unit runs leader-set (including the current unit if it
> is the leader), rather than only when a different unit runs
> leader-set. This way, the leader can make its decisions and exit
> whatever hook triggered it within its 30s lease, and all units can
> perform their long running tasks in the leader-settings-changed hook.
>
> Alternatively, it could kick of an asynchronous task but they don't exist
> yet.
>
> Or would I need to run 'is-leader' in a thread every 30s to keep the
> lease renewed?
>
> --
> Stuart Bishop <stuart.bishop at canonical.com>
>
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