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From Svetoslav Neykov <svetoslav.ney...@cloudsoftcorp.com>
Subject Re: UsageListener: notified of promotion to master?
Date Wed, 22 Mar 2017 19:52:00 GMT
> It feels like (2) is a more generally useful feature to add (for programmatic support,
at least). Does it sound useful for things beyond my use-case?

Yes. I needed this exact functionality last week - for a piece of code shared between all
applications. I ended up writing a poller thread that monitors the state. 
I think it will be a useful thing to add.

Svet.


> On 22.03.2017 г., at 19:11, Aled Sage <aled.sage@gmail.com> wrote:
> 
> Hi all,
> 
> I'm writing a UsageListener [1] that is going to record the Brooklyn instance's apps
in an external inventory. This is mostly straight-forward (except needing the fix at [2]).
> 
> The tricky bit is when a Brooklyn standby instance is promoted to master - I want my
listener to be notified so it can record the identity of the new master Brooklyn for each
of the pre-existing app.
> 
> I don't see anywhere I can get a notification of this. Is there?
> 
> ---
> 
> Possible solutions include:
> 
> 1. Add an additional application event (e.g. state
>   "MANAGEMENT_CHANGED") - the UsageListener would receive this event
>   for every app when it successfully rebinds.
> 2. Register a new kind of listener, to be notified of the management
>   context's state - on becoming "master", my listener could iterate
>   over all the apps.
> 
> I don't particularly like either of those options.
> 
> For (1), it isn't really to do with app "Usage" like the other events.
> 
> For (2), my listener code would be fiddly - I'd need to worry about receiving concurrent
notifications via the normal UsageListener while I'm iterating over the pre-existing apps
(assuming the new listener is called asynchronously, rather than blocking the management context's
startup).
> 
> It feels like (2) is a more generally useful feature to add (for programmatic support,
at least). Does it sound useful for things beyond my use-case?
> 
> Thoughts?
> 
> Aled
> 
> [1] https://github.com/apache/brooklyn-server/blob/master/core/src/main/java/org/apache/brooklyn/core/mgmt/usage/UsageListener.java
> [2] https://github.com/apache/brooklyn-server/pull/606
> 
> 


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