An internal application runs on a single EC2 instance in one Availability Zone. During a power event in that Availability Zone the application was unreachable for four hours. The team wants the cheapest change that keeps it serving through the same kind of event, without moving to another Region. What should they do?
AWS Certified Cloud Practitioner (CLF-C02), objective 3. Cloud technology and services easy
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The options
Correct Run instances in at least two Availability Zones in the same Region, behind a load balancer
Correct. Availability Zones are physically separate, with their own power, cooling and networking, so an event in one leaves the other serving. The load balancer stops sending traffic to the failed zone's targets automatically.
Not correct Take EBS snapshots every hour instead of every day
Wrong. Snapshots protect the data, and more of them shortens how much work you lose. They do nothing to keep the application answering requests, because restoring and relaunching is a manual outage of its own.
Not correct Move to a larger instance type
Wrong. A bigger instance is still one instance in one Availability Zone. Capacity and availability are different problems, and scaling up leaves the failure domain untouched.
Not correct Put Amazon CloudFront in front of the application
Wrong for this. CloudFront caches content at edge locations and would keep serving cached static assets for a while, but every request that has to reach the application still goes to the one instance in the failed zone.
Why
An Availability Zone is one or more discrete data centres with independent power, cooling and physical security, joined to the other zones in its Region by high-bandwidth, low-latency links. That design is what makes 'run it in two zones' the standard unit of high availability: the zones fail independently and the link between them is fast enough to treat them as one deployment. Reach for a second Region for the rarer whole-Region event, or for latency and compliance reasons — not for a data-centre failure.
Where this comes from
- Cited
- AWS exam guide task statement 3.2
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