A payment API must keep serving requests if one datacentre in its Azure region loses power. Legal advice is that the data may not leave the region. Which arrangement satisfies both constraints?

Microsoft Certified: Azure Fundamentals (AZ-900), objective architecture-and-services. Azure architecture and services medium

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The options

Correct Deploy the API across availability zones within that region

Correct. Availability zones are physically separate datacentres inside one region, each with its own power, cooling and networking, so losing one leaves the others serving. Nothing crosses the region boundary.

Not correct Deploy a second copy of the API into the region's pair

Wrong. A paired region does give you independence from a datacentre failure, but it is a different region in a different part of the geography — which is exactly the data movement the legal advice rules out.

Not correct Put the virtual machines into an availability set

Wrong. An availability set spreads instances across fault and update domains inside a single datacentre, so it survives a failed rack or a host reboot but not the loss of the whole datacentre.

Not correct Move the workload to a larger virtual machine size

Wrong. A bigger machine is still one machine in one datacentre. Capacity is not availability, and scaling up changes neither the failure domain nor the number of them you occupy.

Why

Region, availability zone and datacentre form a hierarchy, and each level isolates a different failure. A region is a set of datacentres inside a latency-defined perimeter; an availability zone is one or more of those datacentres with independent power, cooling and networking; an availability set only separates instances inside a single datacentre. Match the failure you fear to the level that isolates it: rack or host to an availability set, whole datacentre to zones, whole region to a second region.

Where this comes from

Cited
Microsoft AZ-900 study guide skill area architecture-and-services.core-architectural-components

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