Nova scheduler first evaluates the configured filters, and it compiles a list of hosts that pass the filters and can be tasked with running the virtual machines instances, after filtering out hosts that don't follow the required capabilities. After Nova scheduler compiles a list of valid candidates to execute the nova request, the scheduler uses weights mechanism to determine which host is the most suitable candidate that executes the request and runs the virtual machine instance. Weights are calculated for each host when a virtual machine instance is to be scheduled, the scheduler calculates host's weight by monitoring resource consumptions of the host. We can set a policy to spread the virtual machine instances across the hosts, or to stack them on a host until resources on that host are exhausted and then schedule virtual machine instances to run on the next best suited host.
Nova scheduler calculates each weight with a configurable multiplier and then...