[openstack-dev] [Ironic] backwards compat issue with PXEDeply and AgentDeploy drivers

Jim Rollenhagen jim at jimrollenhagen.com
Thu Oct 15 00:39:05 UTC 2015

Cross posting to the ops list for visibility.

To follow up on this, we decided not to fix this after all. Besides
Ramesh's (very valid) points below, we realized that fixing this for out
of tree drivers that depended on Kilo behavior would break out of tree
drivers that implemented their own boot mechanism (e.g. virtual media),
or drivers that just generally didn't expect Ironic to handle booting
for them.

Copying my patch to our release notes here, to explain the breakage and
how to fix:

The AgentDeploy and ISCSIDeploy (formerly known as PXEDeploy) now depend
on drivers to mix in an instance of a BootInterface. For drivers that
exist out of tree, that use these deploy drivers directly, an error will
be thrown during deployment. For drivers that expect these deploy classes
to handle PXE booting, please mix in `ironic.drivers.modules.pxe.PXEBoot`
as self.boot. Drivers that handle booting itself (for example, a driver
that implements booting from virtual media) should mix in
`ironic.drivers.modules.fake.FakeBoot` as self.boot, to make calls to the
boot interface a no-op. Additionally, as mentioned before,
`ironic.drivers.modules.pxe.PXEDeploy` has moved to
`ironic.drivers.modules.iscsi_deploy.ISCSIDeploy`, which will break drivers
that mix this class in.

To out of tree driver authors: the Ironic team apologizes profusely for
this inconvenience. We're meeting up in Tokyo to discuss our driver API
and the boundaries there; please join us!

// jim

On Tue, Oct 06, 2015 at 12:05:37PM +0530, Ramakrishnan G wrote:
> Well it's nice to fix, but I really don't know if we should be fixing it.
> As discussed in one of the Ironic meetings before, we might need to define
> what is our driver API or SDK or DDK or whatever we choose to call it .
> Please see inline for my thoughts.
> On Tue, Oct 6, 2015 at 5:54 AM, Devananda van der Veen <
> devananda.vdv at gmail.com> wrote:
> > tldr; the boot / deploy interface split we did broke an out of tree
> > driver. I've proposed a patch. We should get a fix into stable/liberty too.
> >
> > Longer version...
> >
> > I was rebasing my AMTTool driver [0] on top of master because the in-tree
> > one still does not work for me, only to discover that my driver suddenly
> > failed to deploy. I have filed this bug
> >   https://bugs.launchpad.net/ironic/+bug/1502980
> > because we broke at least one out of tree driver (mine). I highly suspect
> > we've broken many other out of tree drivers that relied on either the
> > PXEDeploy or AgentDeploy interfaces that were present in Kilo release. Both
> > classes in Liberty are making explicit calls to "task.driver.boot" -- and
> > kilo-era driver classes did not define this interface.
> >
> I would like to think more about what really our driver API is ? We have a
> couple of well defined interfaces in ironic/drivers/base.py which people
> may follow, implement an out-of-tree driver, make it a stevedore entrypoint
> and get it working with Ironic.
> But
> 1) Do we promise them that in-tree implementations of these interfaces will
> always exist.  For example in boot/deploy work done in Liberty, we removed
> the class PxeDeploy [1].  It actually got broken down to PXEBoot and
> ISCSIDeploy.  In the first place, do we guarantee that they will exist for
> ever in the same place with the same name ? :)
> 2) Do we really promise the in-tree implementations of these interfaces
> will behave the same way ? For example, the broken stuff AgentDeploy which
> is an implementation of our DeployInterface.  Do we guarantee that this
> implementation will always keep doing what ever it was every time code is
> rebased ?
> [1] https://review.openstack.org/#/c/166513/19/ironic/drivers/modules/pxe.py
> >
> > I worked out a patch for the AgentDeploy driver and have proposed it here:
> >   https://review.openstack.org/#/c/231215/1
> >
> > I'd like to ask folks to review it quickly -- we should fix this ASAP and
> > backport it to stable/liberty before the next release, if possible. We
> > should also make a similar fix for the PXEDeploy class. If anyone gets to
> > this before I do, please reply here and let me know so we don't duplicate
> > effort.
> >
> This isn't going to be as same as above as there is no longer a PXEDeploy
> class any more.  We might need to create a new class PXEDeploy which
> probably inherits from ISCSIDeploy and has task.driver.boot worked around
> in the same way as the above patch.
> >
> > Also, Jim already spotted something in the review that is a bit
> > concerning. It seems like the IloVirtualMediaAgentVendorInterface class
> > expects the driver it is attached to *not* to have a boot interface and
> > *not* to call boot.clean_up_ramdisk. Conversely, other drivers may be
> > expecting AgentVendorInterface to call boot.clean_up_ramdisk -- since that
> > was its default behavior in Kilo. I'm not sure what the right way to fix
> > this is, but I lean towards updating the in-tree driver so we remain
> > backwards-compatible for out of tree drivers.
> >
> >
> > -Devananda
> >
> > [0] https://github.com/devananda/ironic/tree/new-amt-driver
> >
> >
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