Open Stack

This is a request for any operators out there that configure nova to set:

[cinder]
cross_az_attach=False

To check out these two bug fixes:

1. https://review.openstack.org/#/c/366724/

This is a case where nova is creating the volume during boot from volume 
and providing an AZ to cinder during the volume create request. Today we 
just pass the instance.availability_zone which is None if the instance 
was created without an AZ set. It's unclear to me if that causes the 
volume creation to fail (someone in IRC was showing the volume going 
into ERROR state while Nova was waiting for it to be available), but I 
think it will cause the later attach to fail here [1] because the 
instance AZ (defaults to None) and volume AZ (defaults to nova) may not 
match. I'm still looking for more details on the actual failure in that 
one though.

The proposed fix in this case is pass the AZ associated with any host 
aggregate that the instance is in.

2. https://review.openstack.org/#/c/469675/

This is similar, but rather than checking the AZ when we're on the 
compute and the instance has a host, we're in the API and doing a boot 
from volume where an existing volume is provided during server create. 
By default, the volume's AZ is going to be 'nova'. The code doing the 
check here is getting the AZ for the instance, and since the instance 
isn't on a host yet, it's not in any aggregate, so the only AZ we can 
get is from the server create request itself. If an AZ isn't provided 
during the server create request, then we're comparing 
instance.availability_zone (None) to volume['availability_zone'] 
("nova") and that results in a 400.

My proposed fix is in the case of BFV checks from the API, we default 
the AZ if one wasn't requested when comparing against the volume. By 
default this is going to compare "nova" for nova and "nova" for cinder, 
since CONF.default_availability_zone is "nova" by default in both projects.

--

I'm requesting help from any operators that are setting 
cross_az_attach=False because I have to imagine your users have run into 
this and you're patching around it somehow, so I'd like input on how you 
or your users are dealing with this.

I'm also trying to recreate these in upstream CI [2] which I was already 
able to do with the 2nd bug.

Having said all of this, I really hate cross_az_attach as it's 
config-driven API behavior which is not interoperable across clouds. 
Long-term I'd really love to deprecate this option but we need a 
replacement first, and I'm hoping placement with compute/volume resource 
providers in a shared aggregate can maybe make that happen.

[1] 
https://github.com/openstack/nova/blob/f278784ccb06e16ee12a42a585c5615abe65edfe/nova/virt/block_device.py#L368
[2] https://review.openstack.org/#/c/467674/

-- 

Thanks,

Matt