Availability set

In the Ultra Transcenders books

AZ-305AZ-104AZ-700AZ-900AZ-802

Each book explains Availability set in context, with comparison tables and the common traps.

Terms in this definition

• Virtual machines

  Infrastructure-as-a-service compute giving complete control of the operating system, making it a fit for lift-and-shift moves and for software relying on OS-level pieces like COM.

• CRUD

  Shorthand for create, read, update and delete, the four basic things you do with data. Data-plane roles in Azure Cosmos DB, for instance, authorise those operations on items.

• Datacenter

  A building packed with racked servers that has its own electricity supply, cooling and network links. Microsoft gathers these buildings into Azure regions, and as a customer you pick the region, never which building your resources land in.

• SLA

  A commitment to a level of uptime, such as 99.99% for VMs spread over availability zones, 99.95% for an availability set and 99.9% for one VM.

• Autoscale

  Azure Monitor capability that adds or removes instances on a schedule or once a metric rule has been true for its full duration. The maximum instance count merely sets a ceiling and never triggers scaling itself.

Related terms

• Basic Load Balancer

  Load Balancer SKU retired on 30 September 2025. It was open by default, worked only with Basic public IPs and lacked zones and HA Ports, and its backend pool was confined to a single availability set, scale set or standalone VM.

• Fault domain

  VMs that share a network switch and power source. To contain rack-level failures, an availability set distributes its VMs across as many as three of these (two in certain regions).

• Placement group

  Scale set grouping that acts as an implicit availability set (five fault domains, five update domains) and is capped at 100 VMs. Setting singlePlacementGroup to false allows as many as 1,000.