Open Stack

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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