Understanding Azure Virtual Machine Availability Sets

Azure Virtual Machine Availability Sets are a free feature of the Azure Virtual Machines (VMs) service. They help ensure that an application running on a set of VMs remains available, despite power failures, network failures, and host OS updates. However, availability sets do not protect against data center-wide failures, they do not implement any kind of failover or coordination of application state among the VMs, and additional VMs are required to maximize guaranteed uptime, which increases the operational cost of an application.

Highly Available Applications as a Service

Azure VM Availability Sets enable creations of groups of VMs that will remain available even if the OS running the hypervisor on the host hardware needs to be updated, or network or power disruption takes out a segment of host hardware within a given data center. Availability sets cannot extend across Azure data centers or regions. Additional steps must be taken if an organization wants to ensure availability in the event of a complete data center failure or catastrophic loss. The Azure management portals or Azure management tools and PowerShell can be used to deploy availability sets.