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Hello,

I haven't investigated thoroughly but I suspect that the bare metal
nodes returned from the hypervisor calls are not handled by the nova
CDM just like you expect. I think we should look into if bare metal
nodes are stored in the compute_model as I think it would more sense to
filter them out.

Overall I think the way Watcher handles bare metal nodes must be
analysed and improved for example the saving energy strategy uses the
ironic client directly and there is currently not a single strategy that
accesses the baremetal_model.

Maybe I have time to test my suspicions in a test environment with both
ironic and hypervisor nodes next week.

On 5/23/19 11:40 PM, Matt Riedemann wrote:
> While working on [1] I noticed that the
> NovaHelper.get_compute_node_by_hostname method is making 3 API calls to
> get the details about a hypervisor:
> 
> 1. listing hypervisors and then filtering client-side by the compute
> service host - this fails if there is not exactly one hypervisor for the
> given compute service host name
> 
> 2. search for the hypervisor given the hypervisor_hostname to get the id
> 
> 3. get the hypervisor details using the id
> 
> My patch is collapsing 2 and 3 into a single API call to nova.
> 
> The question I had was if we need that first call. For all non-ironic
> baremetal nodes, the compute service host and node hypervisor_hostname
> should be identical, so technically we could just search for the
> hypervisor details with the compute service hostname.
> 
> Only in the case of ironic would we potentially get more than one
> hypervisor (node) for a single compute service (host).
> 
> I don't think the nova CDM code really handles baremetal instances at
> all because it's not handling this kind of host:node 1:M cardinality
> elsewhere in the code, but you also can't do most things to optimize
> like cold or live migrating baremetal instances.
> 
> I'm not exactly sure how Watcher deals with ironic but I know there is
> the separate BaremetalClusterDataModelCollector so I'm assuming watcher
> just optimizes for baremetal outside of the nova compute API?
> 
> If this is true, then we can get rid of that first API all noted above
> and I don't need to write a nova spec to add a host filter parameter to
> the GET /os-hypervisors/detail API.
> 
> [1]
> https://review.opendev.org/#/c/661121/2/watcher/common/nova_helper.py@65
>