You plan to run a web application on Azure virtual machines and need protection against a single datacenter failure within an Azure region. Which deployment option should you use?
Availability zones are physically separate datacenters within an Azure region, each with independent power, cooling, and networking. Deploying VMs across zones isolates the workload from a single datacenter failure, so if one zone goes down the application remains available in the others. This is the only option listed that provides datacenter-level resilience.
Why this answer
Availability Zones are physically separate datacenters within an Azure region, each with independent power, cooling, and networking. Deploying your VMs across two or more zones protects against a single datacenter failure because if one zone goes down, the application continues running in the other zone. This meets the requirement for datacenter-level fault tolerance within a single region.
Exam trap
The trap here is that candidates often confuse availability sets (which protect against rack-level failures within one datacenter) with availability zones (which protect against full datacenter failures), leading them to select the cheaper or more familiar option without recognizing the critical difference in fault domain scope.
Why the other options are wrong
An availability set protects against failures within a single datacenter (e.g., rack or update domain failures), not against a full datacenter failure within an Azure region. The question requires protection against a single datacenter failure, which spans across datacenters; availability zones are needed for that.
A proximity placement group reduces network latency between VMs but does not protect against a single datacenter failure; it may even place VMs in the same datacenter, increasing failure risk.
A single VM with premium SSD does not provide protection against a datacenter failure because it is a single instance; if the datacenter hosting that VM fails, the application becomes unavailable.