On 25/07/13 19:07, Bartosz Górski wrote:
We want to start from something simple. At the beginning we are assuming
no dependencies between resources from different region. Our first use
case (the one on the wikipage) uses this assumptions. So this is why it
can be easily split on two separate single region templates.
Our goal is to support dependencies between resources from different
regions. Our second use case (I will add it with more details to the
wikipage soon) is similar to deploying two instances (app server + db
server) wordpress in two different regions (app server in the first
region and db server in the second). Regions will be connected to each
other via VPN connection . In this case configuration of app server
depends on db server. We need to know IP address of created DB server to
properly configure App server. It forces us to wait with creating app
server until db server will be created.
That's still a fairly simple case that could be handled by a pair of
OS::Heat::Stack resources (one provides a DBServerIP output it is passed
as a parameter to the other region using {'Fn::GetAtt':
['FirstRegionStack', 'Outputs.DBServerIP']}. But it's possible to
imagine circumstances where that approach is at least suboptimal (e.g.
when creating the actual DB server is comparatively quick, but we have
to wait for the entire template, which might be slow).
More complicated use case with load balancers and more regions are also
in ours minds.
Good to know, thanks. I'll look forward to reading more about it on the
wiki.
What I'd like to avoid is a situation where anything _appears_ to be
possible (Nova server and Cinder volume in different regions? Sure!
Connect 'em together? Sure!), and the user only finds out later that it
doesn't work. It would be much better to structure the templates in such
a way that only things that are legitimate are expressible. That's not
an achievable goal, but IMO we want to be much closer to the latter than
the former.
cheers,
Zane.
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