Juju Leader Election and Application-Specific Leadership

[Dmitrii Shcherbakov]

I would say:

"You can query an application-specific master and display it to an
operator. However, you cannot set a Juju leader unit using that
information - this is not supported by design"

So, it seems that we need to clearly describe 3 cases:

1. A Juju leader unit configures an application-specific master;
2. A Juju leader displays an application-specific master after it has
been elected internally to the service;
3. The unsupported case: cannot explicitly change unit's leadership.

I think that this will make it very clear even to somebody who doesn't
know much about CAP and protocols such as Paxos and Raft.


Best Regards,
Dmitrii Shcherbakov

On Thu, Apr 6, 2017 at 5:07 PM, Aaron Bentley
<aaron.bentley at canonical.com> wrote:
> On 2017-04-05 09:30 PM, Andrew Wilkins wrote:
>> On Wed, Apr 5, 2017 at 10:26 PM Dmitrii Shcherbakov
>
>>     This doc says
>>     "If the election process is done internally to the service, other code
>>     should be used to signal the leader to Juju.".
>
>> Longer: if your application has its own internal leadership election,
>> then you may wish to present the name of the leader to the user (or
>> other applications), e.g. using application status or relation data.
>> That's what I take "other code" to mean.
>
> "to Juju" makes it sound as if you're signaling Juju itself (i.e the
> controllers), rather than using Juju to signal other applications or the
> user.
>
> Aaron
>
>
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