[ironic][redfish] Breaking (for us) underlying schema/behavior change and what do we do?

Julia Kreger juliaashleykreger at gmail.com
Thu Apr 30 13:38:47 UTC 2020

On Thu, Apr 30, 2020 at 2:49 AM Dmitry Tantsur <dtantsur at redhat.com> wrote:
> Hi,
> On Thu, Apr 30, 2020 at 12:40 AM Julia Kreger <juliaashleykreger at gmail.com> wrote:
>> Greetings fellow awesome sentient beings, and the occasional text indexers!
>> We have a growing conundrum with Redfish.
>> A long time ago, in a red shifted galaxy inhabited by Redfish, a
>> feature was defined early on in the DMTF specification defining a
>> "BootSourceOverrideEnabled" field as part of the ComputerSystem Boot
>> object[0]. This setting, in concert with the
>> "BootSourceOverrideTarget" and "BootSourceOverrideMode" setting
>> allowed Ironic to signal an override preference in regards to what
>> device the machine should boot to.
>> As time as moved forward, schema field descriptions were added, and
>> notes further detailed (observable by looking at [1], see
>> ComputerSystem 1.0.0, 1.5.0, 1.6.0, 1.8.0). One such case, at least
>> depending on what field you looked at also noted that
>> "BootSourceOverrideEnabled" was not possible with the "Continuous"
>> setting, however that was only noted under the one time override
>> option "UefiTargetBootSourceOverride" which is leveraged by the
>> explicit "UEFITarget" target option, at least until ComputerSystem
>> 1.8.0. In ComputerSystem 1.8.0, an explicit note was added into the
>> description text for "BootSourceOverrideEnabled" detailing that one
>> time override use was the only option for UEFI.
>> The published documents also have not been very clear on this, but
>> there are numerous documents on the subject so it seems very easy for
>> the schema details note being added and enhanced in 1.8.0 drove
>> vendors to begin to change the logic around their
>> "BootSourceOverrideEnabled" option to represent what the current
>> documentation detailed, regardless of their schema version. Also, the
>> schema/api versions are disjointed and BMCs out there exist without
>> some of the defined fields. It just kind of is our life with hardware.
>> So why now? The ironic team has had reports recently, across multiple
>> vendors, where with newer firmware versions beginning to implement the
>> changes in schema 1.8.0, where it seems we will no longer be able to
>> use the option we were using, which seemed logical at least when
>> looking at the BMC conformance to the standard. And while some may
>> view the fact it worked on multiple vendors as a regression, I'm sure
>> they see it as a bug as it was seemingly never intended to work that
>> way when we look at the "UEFITargetBootSourceOverride" field notes
>> from the early schemas.
> This nearly yielded a Linus-style response from me. Yes, it IS a breaking change, no matter why it was done and why the initial implementation was wrong from the purism perspective.

I completely agree and truthfully the more I went through historical
schemas, my eyes opened and I went "Oh! *sigh*"

> The first thing we should do to maintain honesty to our consumers is to mark the redfish hardware type and its derivatives (idrac-redfish, more?) as experimental and provide a clear warning in our documentation that the underlying standard and its implementations are unstable. And keep it like that until DMTF and the vendors finally make up their mind.

I think if we do this in redfish driver documentation, it should be
fairly clear. I also suspect we should create a matrix of known
working versions. This would actually help folks like to convey "At
present time, the x vendor BMC is known not to work with our redfish
interfaces at all."

>> tl;dr: As BMC's vendors add the newer schema fields and resulting
>> behavior, the existing redfish driver's ability to assert persistent
>> boot devices breaks.
>> With all of that having been said, I think we should remove our
>> persistent setting capability in our redfish driver, and back port the
>> fix where possible. That being said, this is also a behavior change,
>> so it is time to get everyone's thoughts, since we will need to stress
>> that machines by default should boot from persistent storage instead
>> of network by default.
> This is not just a behavior change, it's also a breaking change. I don't think the boot sequence you mention is the default, I'd rather expect machines (at least in legacy boot mode) to start with PXE booting.
> However, I think I have a work around for that! We could build PXE configuration even for nodes with boot_option:local, so that if a machine boots from the network, we force it to boot from disk via iPXE configuration. Thoughts?

I _suspect_ this would actually be more breaking for operators, at
least for neutron users. For standalone, we may need a knob actually

The reason for neutron is once deployed, there should be no special
DHCP records saying to load iPXE for the host if it is local booting.
If those records are now present, then the machine will always load
iPXE and fail to boot/halt upon not finding out what to do.

For standalone, I suspect a knob may be necessary because bifrost and
other standalone users do operate with overall static dhcp

>> We also need to launch a long term effort to try and duplicate the
>> setting capabilities through the other BMC
>> interfaces/methods/settings, but the variation by vendor is what is
>> going to make it very difficult until the latest redfish schema
>> version is implemented by vendors. Of course, that too may be a while.
> I would like to take a tougher stance on this and say that if vendors want us (or anyone in our situation, really) to support redfish, they need to work with us more closely on the coming redfish changes. Including getting us involved before changes are made to the schemas (to say nothing about actual hardware).

+1000 although I suspect perceptions of competitive advantage will
make discussion or even detailing of pending OEM changes a bit
difficult to be surfaced in an open community, which I think is why,
somehow... we need to become involved in the DMTF to get ahead of the

> Dmitry
>> Thoughts?
>> -Julia
>> [0]: DMTF Redfish Schema Supplement 2019.1a, Page 71:
>> https://www.dmtf.org/sites/default/files/standards/documents/DSP0268_2019.1a.pdf
>>       or the 2016.2 version of the document, Page 16:
>> https://www.dmtf.org/sites/default/files/standards/documents/DSP2046_2016.2.pdf
>>       And the same information can be found in the and 2019.2, 2019.3
>> schema document versions.
>> [1]: Latest schema bundle pack:
>> https://www.dmtf.org/sites/default/files/standards/documents/DSP8010_2019.4.zip

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