Availability sets

High Availability in Azure is primarily achieved through redundancy. Redundancy means that there is more than one resource instance, such that in the event of a failure for a resource, the other takes over. But just having more similar resources does not make them highly available. For example, having more than one virtual machine does not make these virtual machines highly available. Azure provides availability set resources to tag and brings these resources together to form a group. All virtual machines in the availability set become highly available because they are placed on separate physical racks in the Azure data center and each virtual machine is updated one at a time instead of all at the same time. Availability sets provide fault domain and updates domain to achieve this and this is discussed in the next section. In short, availability sets provides redundancy at data center level similar to locally redundant storage.