On 02/29/2016 12:22 PM, Daniel P. Berrange wrote:
There's three core scenarios for hooks
1. Modifying some aspect of the Nova operation
2. Triggering an external action synchronously to some Nova operation
3. Triggering an external action asynchronously to some Nova operation
The Rdo example is falling in scenario 1 since it is modifying the
injected files. I think this is is absolutely the kind of thing
we should explicitly *never* support. When external code can arbitrarily
modify some aspect of Nova operation we're in totally unchartered
territory as to the behaviour of Nova. To support that we'd need to
provide a stable internal API which is just not something we want to
tie ourselves into. I don't know just what the Rdo example is trying
to achieve, but whatever it is, it should be via some supportable API
and not a hook.,
Scenaris 2 and 3 are both valid to consider. Using the notifications
system gets as an asynchronous trigger mechanism, which is probably
fine for many scenarios. The big question is whether there's a
compelling need for scenario two, where the external action blocks
execution of the Nova operation until it has completed its hook.
Even in the case of scenario two it is possible in some cases to use a proxy to
intercept the HTTP request, take action, and then forward it or reject it as
appropriate.
I think the real question is whether there's a need to trigger an external
action synchronously from down in the guts of the nova code.
Chris
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