[openstack-dev] [TripleO] RFC: profile matching

Ben Nemec openstack at nemebean.com
Tue Dec 1 17:55:56 UTC 2015

Sorry for not getting to this earlier.  Some thoughts inline.

On 11/09/2015 08:51 AM, Dmitry Tantsur wrote:
> Hi folks!
> I spent some time thinking about bringing profile matching back in, so 
> I'd like to get your comments on the following near-future plan.
> First, the scope of the problem. What we do is essentially kind of 
> capability discovery. We'll help nova scheduler with doing the right 
> thing by assigning a capability like "suits for compute", "suits for 
> controller", etc. The most obvious path is to use inspector to assign 
> capabilities like "profile=1" and then filter nodes by it.
> A special care, however, is needed when some of the nodes match 2 or 
> more profiles. E.g. if we have all 4 nodes matching "compute" and then 
> only 1 matching "controller", nova can select this one node for 
> "compute" flavor, and then complain that it does not have enough hosts 
> for "controller".
> We also want to conduct some sanity check before even calling to 
> heat/nova to avoid cryptic "no valid host found" errors.
> (1) Inspector part
> During the liberty cycle we've landed a whole bunch of API's to 
> inspector that allow us to define rules on introspection data. The plan 
> is to have rules saying, for example:
>   rule 1: if memory_mb >= 8192, add capability "compute_profile=1"
>   rule 2: if local_gb >= 100, add capability "controller_profile=1"
> Note that these rules are defined via inspector API using a JSON-based 
> DSL [1].
> As you see, one node can receive 0, 1 or many such capabilities. So we 
> need the next step to make a final decision, based on how many nodes we 
> need of every profile.

Is the intent that this will replace the standalone ahc-match call that
currently assigns profiles to nodes?  In general I'm +1 on simplifying
the process (which is why I'm finally revisiting this) so I think I'm
onboard with that idea.

> (2) Modifications of `overcloud deploy` command: assigning profiles
> New argument --assign-profiles will be added. If it's provided, 
> tripleoclient will fetch all ironic nodes, and try to ensure that we 
> have enough nodes with all profiles.
> Nodes with existing "profile:xxx" capability are left as they are. For 
> nodes without a profile it will look at "xxx_profile" capabilities 
> discovered on the previous step. One of the possible profiles will be 
> chosen and assigned to "profile" capability. The assignment stops as 
> soon as we have enough nodes of a flavor as requested by a user.

And this assignment would follow the same rules as the existing AHC
version does?  So if I had a rules file that specified 3 controllers, 3
cephs, and an unlimited number of computes, it would first find and
assign 3 controllers, then 3 cephs, and finally assign all the other
matching nodes to compute.

I guess there's still a danger if ceph nodes also match the controller
profile definition but not the other way around, because a ceph node
might get chosen as a controller and then there won't be enough matching
ceph nodes when we get to that.  IIRC (it's been a while since I've done
automatic profile matching) that's how it would work today so it's an
existing problem, but it would be nice if we could fix that as part of
this work.  I'm not sure how complex the resolution code for such
conflicts would need to be.

> (3) Modifications of `overcloud deploy` command: validation
> To avoid 'no valid host found' errors from nova, the deploy command will 
> fetch all flavors involved and look at the "profile" capabilities. If 
> they are set for any flavors, it will check if we have enough ironic 
> nodes with a given "profile:xxx" capability. This check will happen 
> after profiles assigning, if --assign-profiles is used.
> Please let me know what you think.
> [1] https://github.com/openstack/ironic-inspector#introspection-rules
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