Open Stack

> We have submitted a patch https://review.openstack.org/#/c/11086/ to address
> https://blueprints.launchpad.net/nova/+spec/rebuild-for-ha that simplifies
> recovery from a node failure by introducing an API that recreates an
> instance on *another* host (similar to the existing instance 'rebuild'
> operation). The exact semantics of this operations varies depending on the
> configuration of the instances and the underlying storage topology. For
> example, if it is a regular 'ephemeral' instance, invoking will respawn from
> the same image on another node while retaining the same identity and
> configuration (e.g. same ID, flavor, IP, attached volumes, etc). For
> instances running off shared storage (i.e. same instance file accessible on
> the target host), the VM will be re-created and point to the same instance
> file while retaining the identity and configuration. More details are
> available at http://wiki.openstack.org/Evacuate.
>

If the instance is on shared storage, what does recreate mean? Delete
the old instance and create a new instance, using the same disk image?
Does that mean that the new instance will have a new nova/ec2 id? In
the case where DNS is being used, this would delete the old DNS entry
and create a new DNS entry. This is lossy. If shared storage is
available, the only think that likely needs to happen is for the
instance's host to be updated in the database, and a reboot issued for
the instance. That would keep everything identical, and would likely
be much faster.

- Ryan