Relation dependency

Thu Jan 30 08:30:49 UTC 2014

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On 2014-01-30 5:49, Sameer Zeidat wrote:
> Hello,
> 
> I'm relatively new to juju, and starting to write some charms.
> 
> One thing I'm missing is relation dependency. Say service A can
> join a relation with B and C. I would like for juju to stop A from
> joining C if it has not joined B first. Same also, stop A from
> departing C if it hasn't departed B first.

I'm pretty sure most of this is taken care of in terms of charm
configuration. So if charm A sees C but doesn't yet see B, then it
doesn't configure its connection to C. This is outside of what Juju
specifically controls.

> 
> If this isn't possible then I'd like to at least be able to run a
> hook on C, for instance, if A's relation with B changes.

Generally this is done by reflecting some sort of configuration change
that C can see. So when A is connected to B it sets a value in its
relation with C that C then reacts to.

> 
> Does it make sense?
> 
> Thanks,
> 
> 

Having specific examples can help set the tone for what is actually
being accomplished and how it would be modeled with Juju's relations.

John
=:->

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