[openstack-dev] [nova][ironic] Instance can "migrate" to another node?

Jay Faulkner jay at jvf.cc
Thu Nov 3 16:50:54 UTC 2016


This is all detailed in the release notes for nova here: http://docs.openstack.org/releasenotes/nova/newton.html#new-features — just search for “Ironic”.

Here is the relevant section:
"Note that instances will still be owned by the same nova-compute service for the entire life of the instance, and so the ironic node that instance is on will also be managed by the same nova-compute service until the node is deleted. This also means that removing a nova-compute service will leave instances managed by that service orphaned, and as such most instance actions will not work until a nova-compute service with the same hostname is brought (back) online.

When nova-compute services are brought up or down, the ring will eventually re-balance (when the resource tracker runs on each compute). This may result in duplicate compute_node entries for ironic nodes while the nova-compute service pool is re-balancing. However, because any nova-compute service running the ironic virt driver can manage any ironic node, if a build request goes to the compute service not currently managing the node the build request is for, it will still succeed.”

So essentially what this means is that for provisioned instances, there’s no way to migrate them off of a failed compute host, but unprovisioned node capacity will rebalance automatically between compute hosts when you provision a new one. Essentially if you have a nova compute host fail but want to be able to continue managing instances deployed by it, you’ll have to build another nova-compute host with the same hostname (or CONF.host setting) in order to do anything beyond deleting it.

Hope this helps,
Jay Faulkner

> On Nov 3, 2016, at 3:12 AM, c1 <c1_dx at yahoo.com> wrote:
> Hi al,
> Now, nova’s ironic driver can allow multiple compute services.
> I am not sure that, when a compute node is down. 
> The instances running in it, whether can “migrate” to another compute node(use ironic driver)?
> Thanks
> C1dx 
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