Hi I thought I was late on this thread, but looking at the time stamps, it is just something that escalated very quickly. I am honestly surprised an cross-project interaction option went from 'we don't seem to understand this' to 'deprecation merged' in 4 hours, with only a 12 hour discussion on the mailing list, right at the end of a cycle when we're supposed to be stabilising features.
I proposed a session at the Tokyo summit for a discussion of Cinder AZs, since there was clear confusion about what they are intended for and how they should be configured. Since then I've reached out to and gotten good feedback from, a number of operators. There are two distinct configurations for AZ behaviour in cinder, and both sort-of worked until very recently. 1) No AZs in cinder This is the config where a single 'blob' of storage (most of the operators who responded so far are using Ceph, though that isn't required). The storage takes care of availability concerns, and any AZ info from nova should just be ignored. 2) Cinder AZs map to Nova AZs In this case, some combination of storage / networking / etc couples storage to nova AZs. It is may be that an AZ is used as a unit of scaling, or it could be a real storage failure domain. Eitehr way, there are a number of operators who have this configuration and want to keep it. Storage can certainly have a failure domain, and limiting the scalability problem of storage to a single cmpute AZ can have definite advantages in failure scenarios. These people do not want cross-az attach. My hope at the summit session was to agree these two configurations, discuss any scenarios not covered by these two configuration, and nail down the changes we need to get these to work properly. There's definitely been interest and activity in the operator community in making nova and cinder AZs interact, and every desired interaction I've gotten details about so far matches one of the above models.
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