On Mon, 2024-04-15 at 14:53 +0000, Michael Sherman wrote:
> As per the ironic docs for configuring nova, we’ve had that flag disabled.
> Right now we’re running with a single ironic-conductor, so I don’t think the hash-ring behavior should affect things?
the hash ring behavior is not related to ironic conductors its related to the peer-list option in the nova compute
service config.

the ironic driver only supported a single nova-comptue for the entire ironic
at that time it was possibel to map all your ironics to via that single compute service to a host aggrate/az
in newton https://specs.openstack.org/openstack/nova-specs/specs/newton/implemented/ironic-multiple-compute-hosts.html
support for runnign multiple nova-compute agents with the ironic virt dirver was added.
That intoduced the conceph of a hashring that blanced compute nodes between compute services at runtime based
on teh up state of the compute service. with that change it because impossible to relibly manage
ironic compute nodes with host aggregates as the dirver would uncondtionally blance across all ironic compute services.

with https://specs.openstack.org/openstack/nova-specs/specs/stein/implemented/ironic-conductor-groups.html the ironic
driver was enhanced with awareness of ironic conductor groups. this intoduced a peer-list option and partition key
in pricniapl it was possible to create host aggrate that mapped to conductor groups by incluing all host listed in the
peer_list in the host aggreated

i.e. if you had partition_key=conductor_group_1 peer_list=ironic-1,ironic-2
and you created a host aggreate with ironic-1 and ironic-2 that can work

however its not tested or supproted in general as without carfully configuring the ironic driver
the hashrign can voilate the constraits and move compute_nodes between aggrates by balancing them to compute services
not listed in teh host aggrate

in antelope/bobcat we deprecated the hashring mechaium and intoduced a new ha model and a new ironic sharding mechanium
this was finally implemnted in caracal 2024.1
https://specs.openstack.org/openstack/nova-specs/specs/2024.1/implemented/ironic-shards.html


with this deployment topology it is not guarenteed that ironic will not rebalnce comptue between compute service
which means you can now staticaly map compute services  (and the ironic shard it manages) to a host aggrate again
without worriying that the ironic driver will violate the aggreate expections.

>
> I’m very surprised to hear that nova aggregates are not supported with ironic, it doesn’t seem to be indicated
> anywhere that I could find in the docs? We’ve been using this configuration (Ironic + aggregates) since Rocky, and the
> Blazar project’s support for ironic depends on host aggregates.

we did have this documented at one point but i agree its not something that is widely know and what makes matters worse
is it almost works in some cases.

what people often doen realise is that the host aggregate api
https://docs.openstack.org/api-ref/compute/#host-aggregates-os-aggregates
is written in terms of compute services not compute nodes.
so when trying to use it with ironic they expect to be able to add indivigual ironic server to a host aggreate
https://docs.openstack.org/api-ref/compute/#add-host but they can only add the compute services.

that means you cant use the tenat isolation filter to isolate a subset of ironic nodes for a given tenant.
im not sure how blazar was tryign to use aggreates with ironic but i suspect there integration was incomplete if
not fundementally broken by the limitations of how aggreate function when used with ironic.

if blazar is using placement aggreates rather then nova host aggrate that might change things but there is no
nova api to request a instance ot be created in a placement aggreate.
each ironic node has its own resouce provider in placmenet and placement aggregate work on the resouce provider level
that means you can create aggregate of ironic nodes in placement.

while that is nice since you can use that aggreate in a nova api request that is realy only useful if blazar is
going directly to ironic.