----- Original Message ----- > > -----Original Message----- > > From: Chris Friesen [mailto:[email protected]] > > Sent: 09 April 2014 15:37 > > To: [email protected] > > Subject: Re: [openstack-dev] [Nova] Hosts within two Availability Zones : > > possible or not ? > > > > On 04/09/2014 03:55 AM, Day, Phil wrote: > > > > > I would guess that affinity is more likely to be a soft requirement > > > that anti-affinity, in that I can see some services just not meeting > > > their HA goals without anti-affinity but I'm struggling to think of a > > > use case why affinity is a must for the service. > > > > Maybe something related to latency? Put a database server and several > > public-facing servers all on the same host and they can talk to each other > > with less latency then if they had to go over the wire to another host? > > > I can see that as a high-want, but would you actually rather not start the > service if you couldn't get it ? I suspect not, as there are many other > factors that could affect performance. On the other hand I could imagine a > case where I declare its not worth having a second VM at all if I can't get > it on a separate server. Hence affinity feels more "soft" and > anti-affinity "hard" in terms or requirments.
As the orchestrator if affinity is important to me and it turns out I can't place all of the VMs in the group with affinity, I would likely use the failure to place the second (or subsequent) instance as my cue to rollback and destroy the original VM(s) as well. I don't think either policy is naturally any more hard or soft - it depends on the user and their workloads - this is why I think a "soft" implementation of either filter should be in addition to rather than instead of the existing ones, though "soft" may make more sense for the defaults. Thanks, Steve _______________________________________________ OpenStack-dev mailing list [email protected] http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
