Update domain

Fault domain takes care of unplanned maintenance and updates domain handles planned maintenance. Each virtual machine is also assigned an update domain. There can be as many as 20 update domains in a single availability set. Update domains are nonconfigurable by users. When multiple virtual machines are created, they are placed on separate update domains. If more than 20 virtual machines are provisioned on an availability set, they are placed in a round-robin fashion on these update domains. Update domains take care of planned maintenance.