Open Stack

Hi,

I'm currently working (with dougsz) on adding support for nova cells
v2 in Kolla Ansible. I have a few questions, and things that I'd like
confirming.

1. Is there any benefit to not having a superconductor? Presumably
it's a little more efficient in the single cell case? Also IIUC it
only requires a single message queue so is a little simpler?

2. Do console proxies need to live in the cells? This is what devstack
does in superconductor mode. I did some digging through nova code, and
it looks that way. Testing with novncproxy agrees. This suggests we
need to expose a unique proxy endpoint for each cell, and configure
all computes to use the right one via e.g. novncproxy_base_url,
correct?

3. Should I upgrade the superconductor or conductor service first?

4. Does the cell conductor need access to the API DB?

5. What DB configuration should be used in nova.conf when running
online data migrations? I can see some migrations that seem to need
the API DB, and others that need a cell DB. If I just give it the API
DB, will it use the cell mappings to get to each cell DB, or do I need
to run it once for each cell?

6. After an upgrade, when can we restart services to unpin the compute
RPC version? Looking at the compute RPC API, it looks like the super
conductor will remain pinned until all computes have been upgraded.
For a cell conductor, it looks like I could restart it to unpin after
upgrading all computes in that cell, correct?

7. Which services require policy.{yml,json}? I can see policy
referenced in API, conductor and compute.

I'm trying to design it such that it's possible to deploy a new cell
in an existing environment, and upgrade one cell at a time. Getting
the ordering right for this is fiddly, and I expect I'll be back to
get some eyes on my plan.

Cheers,
Mark