Open Stack

> -----Original Message-----
> From: Chris Friesen [mailto:chris.friesen at windriver.com]
> Sent: 09 April 2014 15:37
> To: openstack-dev at lists.openstack.org
> 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.