On 27/09/13 14:27, Mike Spreitzer wrote:
Stephen Gran <[email protected]> wrote on 09/27/2013 04:26:37 AM:
> I think that your use case for anti-collocation (which is a very good
> and important use case, don't get me wrong) is covered by using
> availability zones/cells/regions and so on as they are, and doesn't
> require much logic internal to Heat beyond obeying the constraint
> specified by a user.
If there are five racks in the system and I want to say that two VMs
should be placed on different racks, how do I say that with AZs without
being overly specific?
If the admins of the openstack install wanted users to be able to select
placement by rack, surely the availability zones would be rack1 - rack5
? In this case, the user would write:
"Resources" : {
"MyASG" : {
"Type" : "AWS::AutoScaling::AutoScalingGroup",
"Properties" : {
"AvailabilityZones" : { "Fn::GetAZs" : ""},
"MinSize" : "2",
"DesiredSize": "2",
"MaxSize" : "2",
}
},
This should naturally implement placement as spread evenly across AZs.
I think maybe this is where I think my disagreement is. Heat should be
able to express a user preference for placement, but only within the
bounds of the policy already created by the admins of the nova install.
To have Heat have more knowledge than what is available via the nova
API seems overcomplicated and fragile to me. If the nova API should
grow some extensions to make more complicated placement algorithms
available, then that's an argument that might have legs.
Cheers,
--
Stephen Gran
Senior Systems Integrator - theguardian.com
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