[Openstack] [Heat] Autoscaling, scale VMs on different hosts

Deepthi Dharwar deepthi at linux.vnet.ibm.com
Mon Dec 8 15:07:25 UTC 2014

On 12/08/2014 08:13 AM, Qiming Teng wrote:
> On Fri, Dec 05, 2014 at 04:13:49PM +0530, Deepthi Dharwar wrote:
>> Hi all,
>> I have been using the autoscaling HOT template and have been successful
>> in running it. I do see number of VMs increasing and decreasing based on
>> my scaling metrics. However, I do have one extra requirement, i.e deploy
>> the VM on a different host.
>> The scenario being, if I have a VM1 running on a particular host1 and
>> when comes a need to  scale up based on the metrics, I want the new VM2
>> to be deployed on a different host i.e host2.
>> Scheduler does provide a filter i.e DifferentHostFilter, where one can
>> deploy an instance on a different host from a set of instances. However
>> to provide this as a part of scheduler hint in the HOT template, one
>> would need the UUID of previous spawned VM. Is there a way to get this
>> data via the HOT template and also pass it as different_host hint for
>> the new VM ?
> If Nova forces you to specify a UUID of an existing VM when providing a
> scheduler hint, that means it is not a good interface IMO.  Personally,
> I would prefer the Nova server-group APIs[1] on which have been quite some
> disbutes whether they belong to Nova.


>> So, if I have 2 hosts and have my webserver VM1 running on the host1,
>> ideally i would want VM2 webserver to be running on host2.
>> Is there an elegant way to achieve this ?
> I don't know an easy way to do this today though I can feel the need to
> support this in future.  Basically, there are discrete policies that can
> be associated with a group of resources, i.e. creation-policy,
> scheduling-policy, termination-policy, availability-policy, ... to name
> a few.  There is a work thread on improving this [2], but users have to
> be patient at the moment.

Thank you for the pointers.


> Thanks,
>   Qiming
> [1]
> http://developer.openstack.org/api-ref-compute-v2-ext.html#ext-os-server-groups
> [2]
> http://lists.openstack.org/pipermail/openstack-dev/2014-November/051764.html
>> Please help!
>> Regards,
>> Deepthi
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