Juju Actions - Use Cases

[Michael Nelson]

On Thu, Sep 11, 2014 at 3:41 AM, Aaron Bentley
<aaron.bentley at canonical.com> wrote:
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> On 14-09-10 01:29 PM, Charles Butler wrote:
>> There's nothing that says the hook cannot call config to make it
>> reproduce-able
>
> But if it's a config variable, then config-changed needs to be able to
> handle changes to it.  If config-changed can handle it, then you don't
> need an action.

True that you don't need it, but it still may have a benefit. We have
a config variable, build_label, which when set to r255 it will (1)
download r255/my-tarball.tgz from a swift container, (2) extract it in
right directory, (3) set the perms correctly, and then (4) finally
switches the symlink and restarts.

But we've also got a "preload" action that Simon recently added, which
enables our charms to do 1, 2 and 3 on all the units, so that when the
config is changed to build_label=r255, any unit which was already
preloaded will just switch the symlink and restart. So it's
reproducible (ie. will still work fine if you preload, then add 2
units, then set the build_label), but is a little faster and more
importantly, allows us to reduce what's happening at the actual
rollout time to symlink+restart.

-Michael

>
> Aaron
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