Open Stack

> On 26 Oct 2018, at 1:42 am, Dan Smith <dms at danplanet.com> wrote:
> 
>> I guess our architecture is pretty unique in a way but I wonder if
>> other people are also a little scared about the whole all DB servers
>> need to up to serve API requests?
> 
> When we started down this path, we acknowledged that this would create a
> different access pattern which would require ops to treat the cell
> databases differently. The input we were getting at the time was that
> the benefits outweighed the costs here, and that we'd work on caching to
> deal with performance issues if/when that became necessary.
> 
>> I’ve been thinking of some hybrid cellsv1/v2 thing where we’d still
>> have the top level api cell DB but the API would only ever read from
>> it. Nova-api would only write to the compute cell DBs.
>> Then keep the nova-cells processes just doing instance_update_at_top to keep the nova-cell-api db up to date.
> 
> I'm definitely not in favor of doing more replication in python to
> address this. What was there in cellsv1 was lossy, even for the subset
> of things it actually supported (which didn't cover all nova features at
> the time and hasn't kept pace with features added since, obviously).
> 
> About a year ago, I proposed that we add another "read only mirror"
> field to the cell mapping, which nova would use if and only if the
> primary cell database wasn't reachable, and only for read
> operations. The ops, if they wanted to use this, would configure plain
> old one-way mysql replication of the cell databases to a
> highly-available server (probably wherever the api_db is) and nova could
> use that as a read-only cache for things like listing instances and
> calculating quotas. The reaction was (very surprisingly to me) negative
> to this option. It seems very low-effort, high-gain, and proper re-use
> of existing technologies to me, without us having to replicate a
> replication engine (hah) in python. So, I'm curious: does that sound
> more palatable to you?

Yeah I think that could work for us, so far I can’t think of anything better. 

Thanks,
Sam


> 
> --Dan