On 31 July 2015 at 20:40, Mike Perez <thin...@gmail.com> wrote: > > Regardless, I want to know if we really need a DLM. Does Ceilometer > really need a DLM? Does Cinder really need a DLM? Can we just use a > hash ring solution where operators don't even have to know or care > about deploying a DLM and running multiple instances of Cinder manager > just works? > >
There's a lot of circling around here about what we're trying to achieve with 'H/A'. Some people are interested in performance. For them, a hash ring solution (deterministic load balancing) is fine. If the aim is availability (as mine is) then I can't see how it helps. I might be missing something, of course - if so, I'm happy to be corrected. To be clear, my aim with H/A is to remove the situation where a single node failure removes the control path for my storage. Currently, the only way to avoid this is to use something like pacemaker to monitor the c-vol services. Extensive experience suggests that pacemaker is a complex, fragile piece of software. Every component of cinder except c-vol can be deployer active/active[/active/...] - I'm aiming for consistency of approach if nothing else. If it ends up that trying to fix this adds too much complexity and/or fragility to cinder itself, then I can accept that - once whatever we do ends up being worse than pacemaker, we've taken a significant step backwards. Regardless of how H/A discussions go, the first part of Gorka's patch can certainly be used to fix a few of the API races we have, and can do so with rather nice, elegant, easy to understand code, so I think the whole process has been productive whatever the H/A outcome. -- Duncan Thomas
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