Affinity and anti-affinity rules allow you to spread a group of virtual machines across different ESXi hosts or keep a group of virtual machines on a particular ESXi host.
An affinity rule places a group of virtual machines on a specific host so that you can easily audit the usage of those virtual machines. An anti-affinity rule places a group of virtual machines across different hosts, which prevents all virtual machines from failing at once in the event that a single host fails.
If the affinity or anti-affinity rules cannot be satisfied, this prevents the virtual machines added to the rule from powering on.
