Availability sets are a basic way to let Microsoft Azure know that these two virtual machines belong to a cluster or application group and are now allowed to go down together.
For virtual machines within a availability Azure manages that these machines run within different fault and update domains of an Azure region:
- Update domain: Update domain in Azure means, that all physical servers in on update domain will get host updates like firmware, drivers and OS updates at the same time.
- Fault domain: Fault domain in Azure means that all servers in these domains run in the same fire sections, with same air condition or electrical source. Which means all physical servers within in those domains, can have an outage at the same time.
The following diagram a schematic view on the distribution of a VM within a availability set:
With Azure virtual machine Managed Disks, there is an additional option which comes with availability sets. Azure takes also care that Managed Disks for those...