Open Stack

Hello All,
              I would like to know if its possible to set
"ram_allocation_ratio" per compute node or at least per Availability
zone.
I tried setting that per compute nodes,but i get "no hosts found"
message when allocation ratio reaches default 1.5 .Changing it on
controller fixes this,but i dont want it to be set globally across all
AZ.Is it possible?

Regards,