[nova] Validation for requested host/node on server create
---- On Fri, 24 May 2019 07:02:15 +0900 Matt Riedemann <mriedemos at gmail.com> wrote ----
> On 5/22/2019 5:13 PM, Matt Riedemann wrote:
> > 3. Validate both the host and node in the API. This can be broken down:
> > a) If only host is specified, do #2 above.
> > b) If only node is specified, iterate the cells looking for the node (or
> > query a resource provider with that name in placement which would avoid
> > down cell issues)
> > c) If both host and node is specified, get the HostMapping and from that
> > lookup the ComputeNode in the given cell (per the HostMapping)
> > Pros: fail fast behavior in the API if either the host and/or node do
> > not exist
> > Cons: performance hit in the API to validate the host/node and
> > redundancy with the scheduler to find the ComputeNode to get its uuid
> > for the in_tree filtering on GET /allocation_candidates.
> > Note that if we do find the ComputeNode in the API, we could also
> > (later?) make a change to the Destination object to add a node_uuid
> > field so we can pass that through on the RequestSpec from
> > API->conductor->scheduler and that should remove the need for the
> > duplicate query in the scheduler code for the in_tree logic.
> > I'm personally in favor of option 3 since we know that users hate
> > NoValidHost errors and we have ways to mitigate the performance overhead
> > of that validation.
> > Note that this isn't necessarily something that has to happen in the
> > same change that introduces the host/hypervisor_hostname parameters to
> > the API. If we do the validation in the API I'd probably split the
> > validation logic into it's own patch to make it easier to test and
> > review on its own.
> >  https://review.opendev.org/#/c/645520/
> > 
> > https://github.com/openstack/nova/blob/2e85453879533af0b4d0e1178797d26f026a9423/nova/scheduler/utils.py#L528
> >  https://docs.openstack.org/nova/latest/admin/availability-zones.html
> Per the nova meeting today  it sounds like we're going to go with
> option 3 and do the validation in the API - check hostmapping for the
> host, check placement for the node, we can optimize the redundant
> scheduler calculation for in_tree later. For review and test sanity I
> ask that the API validation code comes in a separate patch in the series.
+1 on option3. For more optimization, can we skip b) and c) for non-baremental case
assuming if there is Hostmapping then node also will be valid.