First customer pain point pull request - default-hook

[Gustavo Niemeyer]

I don't think I fully understand the proposal there. To have such a
"something-changed" hook, we ought to have a better mechanism to tell
*what* actually changed. In other words, we have a number of hooks
that imply a state transition or a specific notification ("install",
"start", "config-changed", "leader-elected" coming, etc). Simply
calling out the charm saying "stuff changed" feels like a bad
interface, both in performance terms (we *know* what changed) and in
user experience (how do people use that!?).

I understand the underlying problem William is trying to solve but the
current proposal doesn't seem like a complete solution on its own, and
it also seems to change the existing understanding of the model
completely. The proposed default-hooks is a trivial change to the
existing well known workflow.



On Sun, Aug 17, 2014 at 2:30 AM, John Meinel <john at arbash-meinel.com> wrote:
> I'd just like to point out that William has thought long and hard about this
> problem, and what semantics make the most sense (does it get called for any
> hook, does it always get called, does it only get called when the hook
> doesn't exist, etc).
> I feel like had some really good decisions on it:
> https://docs.google.com/a/canonical.com/document/d/1V5G6v6WgSoNupCYcRmkPrFKvbfTGjd4DCUZkyUIpLcs/edit#
>
> default-hook sounds (IMO) like it may run into problems where we do logic
> based on whether a hook exists or not. There are hooks being designed like
> leader-election and address-changed that might have side effects, and
> default-hook should (probably?) not get called for those.
>
> I'd just like us to make sure that we actually think about (and document)
> what hooks will fall into this, and make sure that it always makes sense to
> rebuild the world on every possible hook (which is how charm writers will be
> implementing default-hook, IMO).
>
> John
> =:->
>
>
>
> On Sat, Aug 16, 2014 at 1:02 AM, Aaron Bentley <aaron.bentley at canonical.com>
> wrote:
>>
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> On 14-08-15 04:36 PM, Nate Finch wrote:
>> > There's new hook in town: default-hook.  If it exists and a hook
>> > gets called that doesn't have a corresponding hook file,
>> > default-hook gets called with the name of the original hook as its
>> > first argument (arg[1]).
>> >
>> > That's it.
>>
>> Nice!  Thank you.
>>
>> Aaron
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-- 

gustavo @ http://niemeyer.net