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Hi,

At the recent kolla virtual PTG [1] we had a good discussion about
adding support for multiple nova cells in kolla-ansible. We agreed a
key requirement is to be able to perform operations on one or more
cells without affecting the rest for damage limitation. This also
seems like it would apply to upgrades. We're seeking input on
ordering. Looking at the nova upgrade guide [2] I might propose
something like this:

1. DB syncs
2. Upgrade API, super conductor

For each cell:
3a. Upgrade cell conductor
3b. Upgrade cell computes

4. SIGHUP all services
5. Run online migrations

At some point in here we also need to run the upgrade check.
Presumably between steps 1 and 2?

It would be great to get feedback both from the nova team and anyone
running cells
Thanks,
Mark

[1] https://etherpad.openstack.org/p/kolla-train-ptg
[2] https://docs.openstack.org/nova/latest/user/upgrade.html