[openstack-dev] [Magnum][Heat] Expression of Bay Status

Angus Salkeld asalkeld at mirantis.com
Tue Mar 10 03:47:50 UTC 2015

On Tue, Mar 10, 2015 at 8:53 AM, Adrian Otto <adrian.otto at rackspace.com>

> Magnum Team,
> In the following review, we have the start of a discussion about how to
> tackle bay status:
> https://review.openstack.org/159546
> I think a key issue here is that we are not subscribing to an event feed
> from Heat to tell us about each state transition, so we have a low degree
> of confidence that our state will match the actual state of the stack in
> real-time. At best, we have an eventually consistent state for Bay
> following a bay creation.
Hi Adrian

Currently Heat does not an "event stream", but instead an event table and
REST resource. This sucks as you have to poll it.
We have been long wanting some integration with Zaqar - we are all
convinced, just needs someone to do the work.
So the idea here is we send user related events via a Zaqar queue and the
user (Magnum) subscribes and get events.
>From last summit https://etherpad.openstack.org/p/kilo-heat-summit-topics
(see line 73).

> Here are some options for us to consider to solve this:
> 1) Propose enhancements to Heat (or learn about existing features) to emit
> a set of notifications upon state changes to stack resources so the state
> can be mirrored in the Bay resource.

See above, you have anyone to drive this?

> 2) Spawn a task to poll the Heat stack resource for state changes, and
> express them in the Bay status, and allow that task to exit once the stack
> reaches its terminal (completed) state.
> 3) Don’t store any state in the Bay object, and simply query the heat
> stack for status as needed.

If it's not too frequent then this might be your best bet until we get "1)".

Hope this helps

> Are each of these options viable? Are there other options to consider?
> What are the pro/con arguments for each?
> Thanks,
> Adrian
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