This guide explains how to disable a compute node (so that no new instances will be scheduled on this node):
Step-by-step guide
openstack compute service set --disable <hostname> nova-compute
E.g.:
openstack compute service set --disable compute-01.cloud.pd.infn.it nova-compute
To check:
openstack compute service list
To re-enable the compute node:
openstack compute service set --enable <hostname> nova-compute
E.g.:
openstack compute service set --enable compute-01.cloud.pd.infn.it nova-compute