Relation addresses

[Andrew Wilkins]

On Tue, Jun 17, 2014 at 3:42 PM, William Reade <william.reade at canonical.com>
wrote:

> On Tue, Jun 17, 2014 at 6:39 AM, Andrew Wilkins <
> andrew.wilkins at canonical.com> wrote:
>
>> Hi all,
>>
>> I've started looking into fixing
>> https://bugs.launchpad.net/juju-core/+bug/1215579. The gist is, we
>> currently set private-address in relation settings when a unit joins, but
>> never update it.
>>
>> I've had some preliminary discussions with John, William and Dimiter, and
>> came up with the following proposal:
>> https://docs.google.com/a/canonical.com/document/d/1jCNvS7sSMZqtSnup9rDo3b2Wwgs57NimqMorXr9Ir-o/edit
>>
>> If you're a charm author, particularly if you work on "proxy charms",
>> please take a look at this and let me know of any concerns or suggestions.
>> I have opened up comments on the doc.
>>
>> In a nutshell:
>>  - There will be a new hook, relation-address-changed, and a new tool
>> called address-get.
>>  - The hook will be called when the relation's address has changed, and
>> the tool can be called to obtain the address. If the hook is not
>> implemented, the private-address setting will be updated. Otherwise it is
>> down to you to decide how you want to react to address changs (e.g. for
>> proxy charms, probably just don't do anything.)
>>
>
> I think that what the proposal says is subtly different: that is, that we
> *will* update the private-address setting for that foo relation at the
> start of the foo-relation-address-changed hook, but that it won't be
> propagated further until that hook is committed.
>
> The upshot is that if you're *not* a proxy charm, you can *probably*
> ignore the relation-address-changed hook [0]; but if you *are* a proxy
> charm, you must (almost) certainly overwrite the new private-address
> setting with that of the endpoint you're proxying.
>

Thanks, you're quite right, and the wording in the doc is what is expected
of charm authors.


> IMO this behaviour is more consistent and predictable than behaving
> differently depending on whether or not a particular hook is implemented.
>
> Cheers
> William
>
> [0] some interfaces have their own language -- say "host" -- and they'll
> have to be responsible for updating themselves.
>
>>
>> Thanks,
>> Andrew
>>
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>>
>
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