Using Openstack scheduler hints with juju

James Troup james.troup at
Mon Feb 4 14:00:07 UTC 2013

William Reade <william.reade at> writes:

> On Fri, 2013-02-01 at 15:23 +0100, William Reade wrote:
> For the purposes of argument, how well would something like the following work to fulfil the goals that led to the os-scheduler-hints work?
>>   * Units of service X should be deployed to instances running on
>>     different physical machines ("I want my mongos to be separated").

FWIW, this is the use case that we care about - a lot.

> juju set-constraints -s mongo avoid-services=mongo

While this would work and be better than nothing, it would be more
strict than necessary.

My requirement is simply that any given service is not vulnerable to any
one physical node failing.  So for example, the following hypothetical
placement would meet my requirements, but wouldn't be allowed by your
proposed constraints:

 Hypervisor A:
  - haproxy/1
  - haproxy/3
 Hypervisor B:
  - haproxy/2
  - haproxy/4

Whether this matters in the real world, I'm not sure.  I expect that in
small clouds and/or clouds with a lot of environments and services, it

One way of describing what I'm looking for might be:

  juju set-constraints -s haproxy min-physical-redundancy=2

(Or if we want to get real fancy, it could accept arguments of the form
 'n+1' - how we define 'n' in that case is left as an exercise to the
 reader ;-)


More information about the Juju mailing list