[openstack-dev] [ironic] ironic and traits

Eric Fried openstack at fried.cc
Mon Oct 16 16:55:15 UTC 2017

* Adding references to the specs: ironic side [1]; nova side [2] (which
just merged).

* Since Jay is on vacation, I'll tentatively note his vote by proxy [3]
that ironic should be the source of truth - i.e. option (a).  I think
the upshot is that it's easier for Ironic to track and resolve conflicts
than for the virt driver to do so.

> The downside is obvious - with a lot of deploy templates
> available it can be a lot of manual work.

* How does option (b) help with this?

* I suggested a way to maintain the "source" of a trait (operator,
inspector, etc.) [4] which would help with resolving conflicts.
However, I agree it would be better to avoid this extra complexity if

* This is slightly off topic, but it's related and will eventually need
to be considered: How are you going to know whether a
UEFI-capable-but-not-enabled node should have its UEFI mode turned on?
Are you going to parse the traits specified in the flavor?  (This might
work for Ironic, but will be tough in the general case.)

[1] https://review.openstack.org/504531
[2] https://review.openstack.org/507052

On 10/16/2017 11:24 AM, Dmitry Tantsur wrote:
> Hi all,
> I promised John to dump my thoughts on traits to the ML, so here we go :)
> I see two roles of traits (or kinds of traits) for bare metal:
> 1. traits that say what the node can do already (e.g. "the node is
> doing UEFI boot")
> 2. traits that say what the node can be *configured* to do (e.g. "the node can
> boot in UEFI mode")
> This seems confusing, but it's actually very useful. Say, I have a flavor that
> requests UEFI boot via a trait. It will match both the nodes that are already in
> UEFI mode, as well as nodes that can be put in UEFI mode.
> This idea goes further with deploy templates (new concept we've been thinking
> about). A flavor can request something like CUSTOM_RAID_5, and it will match the
> nodes that already have RAID 5, or, more interestingly, the nodes on which we
> can build RAID 5 before deployment. The UEFI example above can be treated in a
> similar way.
> This ends up with two sources of knowledge about traits in ironic:
> 1. Operators setting something they know about hardware ("this node is in UEFI
> mode"),
> 2. Ironic drivers reporting something they
>   2.1. know about hardware ("this node is in UEFI mode" - again)
>   2.2. can do about hardware ("I can put this node in UEFI mode")
> For case #1 we are planning on a new CRUD API to set/unset traits for a node.
> Case #2 is more interesting. We have two options, I think:
> a) Operators still set traits on nodes, drivers are simply validating them. E.g.
> an operators sets CUSTOM_RAID_5, and the node's RAID interface checks if it is
> possible to do. The downside is obvious - with a lot of deploy templates
> available it can be a lot of manual work.
> b) Drivers report the traits, and they get somehow added to the traits provided
> by an operator. Technically, there are sub-cases again:
>   b.1) The new traits API returns a union of operator-provided and
> driver-provided traits
>   b.2) The new traits API returns only operator-provided traits; driver-provided
> traits are returned e.g. via a new field (node.driver_traits). Then nova will
> have to merge the lists itself.
> My personal favorite is the last option: I'd like a clear distinction between
> different "sources" of traits, but I'd also like to reduce manual work for
> operators.
> A valid counter-argument is: what if an operator wants to override a
> driver-provided trait? E.g. a node can do RAID 5, but I don't want this
> particular node to do it for any reason. I'm not sure if it's a valid case, and
> what to do about it.
> Let me know what you think.
> Dmitry
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