Three virtual machines form a quorum-based cluster in a region that has no availability zones. You want them placed so that neither a single rack losing power nor a single batch of planned host maintenance can take all three at once. What do you configure?
Microsoft Certified: Azure Fundamentals (AZ-900), objective architecture-and-services. Azure architecture and services medium
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The options
Correct Place all three in one availability set
Correct. Azure spreads a set's members across fault domains — racks with their own power and network — and across update domains, which are rebooted at different times during planned maintenance. That covers both failures named.
Not correct Place each machine in its own resource group
Wrong. Resource groups are management containers with no bearing on physical placement; three groups and one group put the machines on exactly the same hardware.
Not correct Place each machine in a separate subscription
Wrong for the same reason, with added cost: you have fragmented billing and access control across three subscriptions and gained no placement guarantee at all.
Not correct Give each machine a different size
Wrong. Size decides CPU, memory and disk throughput. It does not decide which rack the machine lands on or when its host is rebooted.
Why
The two domains inside an availability set answer two different questions: fault domains protect you against something breaking (shared power, shared top-of-rack network), and update domains protect you against something being updated (hosts rebooted in batches for planned maintenance). Both operate inside a single datacentre, which is why availability zones are the next level up when a region offers them.
Where this comes from
- Cited
- Microsoft AZ-900 study guide skill area architecture-and-services.compute-and-networking
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