From: Jay Pipes []
Sent: Monday, October 23, 2017 12:20 PM
To: OpenStack Development Mailing List <>
Subject: Re: [openstack-dev] [ironic] ironic and traits

Writing from my phone... May I ask that before you proceed with any plan that 
uses traits for state information that we have a hangout or videoconference to 
discuss this? Unfortunately today and tomorrow I'm not able to do a hangout but 
I can do one on Wednesday any time of the day.

[Mooney, Sean K] on the uefi boot topic I did bring up at the ptg that we 
wanted to standardizes tratis for “verified boot”
that included a trait for uefi secure boot enabled and to indicated a hardware 
root of trust, e.g. intel boot guard or similar
we distinctly wanted to be able to tag nova compute hosts with those new traits 
so we could require that vms that request
a host with uefi secure boot enabled and a hardware root of trust are scheduled 
only to those nodes.

There are many other examples that effect both vms and bare metal such as, 
ecc/interleaved memory, cluster on die,
l3 cache code and data prioritization, vt-d/vt-c, HPET, Hyper threading, power 
states … all of these feature may be present on the platform
but I also need to know if they are turned on. Ruling out state in traits means 
all of this logic will eventually get pushed to scheduler filters
which will be suboptimal long term as more state is tracked. Software defined 
infrastructure may be the future but hardware defined software
is sadly the present…

I do however think there should be a sperateion between asking for a host that 
provides x with a trait and  asking for x to be configure via
A trait. The trait secure_boot_enabled should never result in the feature being 
enabled It should just find a host with it on. If you want
To request it to be turned on you would request a host with secure_boot_capable 
as a trait and have a flavor extra spec or image property to request
Ironic to enabled it.  these are two very different request and should not be 
treated the same.

Lemme know!

On Oct 23, 2017 5:01 AM, "Dmitry Tantsur" 
<<>> wrote:
Hi Jay!
I appreciate your comments, but I think you're approaching the problem from 
purely VM point of view. Things simply don't work the same way in bare metal, 
at least not if we want to provide the same user experience.

On Sun, Oct 22, 2017 at 2:25 PM, Jay Pipes 
<<>> wrote:
Sorry for delay, took a week off before starting a new job. Comments inline.

On 10/16/2017 12:24 PM, 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")

There's only one role for traits. #2 above. #1 is state information. Traits are 
not for state information. Traits are only for communicating capabilities of a 
resource provider (baremetal node).

These are not different, that's what I'm talking about here. No users care 
about the difference between "this node was put in UEFI mode by an operator in 
advance", "this node was put in UEFI mode by an ironic driver on demand" and 
"this node is always in UEFI mode, because it's AARCH64 and it does not have 
BIOS". These situation produce the same result (the node is booted in UEFI 
mode), and thus it's up to ironic to hide this difference.

My suggestion with traits is one way to do it, I'm not sure what you suggest 

For example, let's say we add the following to the os-traits library [1]


The Ironic administrator would add all RAID-related traits to the baremetal 
nodes that had the *capability* of supporting that particular RAID setup [2]

When provisioned, the baremetal node would either have RAID configured in a 
certain level or not configured at all.

A very important note: the Placement API and Nova scheduler (or future Ironic 
scheduler) doesn't care about this. At all. I know it sounds like I'm being 
callous, but I'm not. Placement and scheduling doesn't care about the state of 
things. It only cares about the capabilities of target destinations. That's it.

Yes, because VMs always start with a clean state, and hypervisor is there to 
ensure that. We don't have this luxury in ironic :) E.g. our SNMP driver is not 
even aware of boot modes (or RAID, or BIOS configuration), which does not mean 
that a node using it cannot be in UEFI mode (have a RAID or BIOS 
pre-configured, etc, etc).

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.

No :) It will only match nodes that have the UEFI capability. The set of 
providers that have the ability to be booted via UEFI is *always* a superset of 
the set of providers that *have been booted via UEFI*. Placement and scheduling 
decisions only care about that superset -- the providers with a particular 

Well, no, it will. Again, you're purely basing on the VM idea, where a VM is 
always *put* in UEFI mode, no matter how the hypervisor looks like. It is 
simply not the case for us. You have to care what state the node is, because 
many drivers cannot change this state.

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
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")

You're correct that both pieces of information are important. However, only the 
"can do about hardware" part is relevant to Placement and Nova.
For case #1 we are planning on a new CRUD API to set/unset traits for a node.

I would *strongly* advise against this. Traits are not for state information.

Instead, consider having a DB (or JSON) schema that lists state information in 
fields that are explicitly for that state information.

For example, a schema that looks like this:

  "boot": {
    "mode": <one of 'bios' or 'uefi'>,
    "params": <dict>
  "disk": {
    "raid": {
      "level": <int>,
      "controller": <one of 'sw' or 'hw'>,
      "driver": <string>,
      "params": <dict>
    },  ...
  "network": {

etc, etc.

Don't use trait strings to represent state information.

I don't see an alternative proposal that will satisfy what we have to solve.

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; 
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

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.


[2] Based on how many attached disks the node had, the presence and abilities 
of a hardware RAID controller, etc

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