How to force openstack to resize on the same host

I want to force openstack to resize every instance on the same host if it is possible to do. How can I do that? Before that, why should I do that. Here, you have a use case, you are on a private cloud and running some critical virtual machines in a very limited resources. You should take a turn to do this.

Add the following lines in /etc/nova/nova.conf

allow_resize_to_same_host=True
scheduler_default_filters=AllHostsFilter

Restart Services

service nova-scheduler restart
service nova-compute restart