[openstack-dev] [Scheduler] New scheduler feature - VM Ensembles

Russell Bryant rbryant at redhat.com
Tue Jan 22 15:03:21 UTC 2013

On 01/08/2013 08:27 AM, Gary Kotton wrote:
> Hi,
> The link
> https://docs.google.com/document/d/1bAMtkaIFn4ZSMqqsXjs_riXofuRvApa--qo4UTwsmhw/edit
> <https://docs.google.com/document/d/1bAMtkaIFn4ZSMqqsXjs_riXofuRvApa--qo4UTwsmhw/edit>
> introduces the concept of a VM ensemble or VM group into Nova. An
> ensemble will provide the tenant the ability to group together VMs that
> provide a certain service or part of the same application. More
> specifically it enables configuring scheduling policies per group. This
> will in turn allow for a more robust and resilient service.
> Specifically, it will allow a tenant to deploy a multi-VM application
> that is designed for VM fault tolerance in a way that application
> availability is actually resilient to physical host failure.
> Any inputs and comments will be greatly appreciated.

I just read over the blueprint and document for this.

My gut reaction is that this seems to be bleeding some of what Heat does
into Nova, which I don't like.

The document provides an example using the existing different_host
scheduler hint.  It shows how it might schedule things in a way that
won't work, but only if the compute cluster is basically running out of
capacity.  I'm wondering how realistic of a problem this example is

The document mentions that when requesting N instances, specifying that
anti-affinity is required for the hosts is not possible.  Perhaps that's
something that could be added.

Russell Bryant

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