SOA-C02 Reliability and Business Continuity Practice Question

A company runs a critical application on a single Amazon EC2 instance. The SysOps administrator needs to ensure that if the instance fails, a new instance is automatically provisioned in a different Availability Zone. Which configuration should the administrator implement?

⚠ Common exam trap

Many candidates confuse the health-check and failover capabilities of Route 53 or ELB with the automatic instance provisioning provided by Auto Scaling groups, mistakenly thinking DNS or load balancer health checks alone can replace a failed instance.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Create an Auto Scaling group with the instance in multiple Availability Zones

An Auto Scaling group (ASG) can be configured with a minimum, desired, and maximum size of 1, spanning multiple Availability Zones (AZs). When the EC2 instance fails, the ASG health check replacement mechanism automatically terminates the unhealthy instance and launches a new one in a different AZ, ensuring the application remains available across AZ boundaries without manual intervention.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
Create an Auto Scaling group with the instance in multiple Availability Zones
Why this is correct
An Auto Scaling group with a desired capacity of 1 spanning multiple Availability Zones is the correct choice because it provides automatic self-healing: if the instance becomes unhealthy or fails, the ASG terminates it and launches a replacement in another AZ to return to desired capacity. Unlike the other options, this directly restores the EC2 instance itself, not just traffic routing. The ASG also monitors health via EC2 status checks and can integrate with an Elastic Load Balancer for additional health checks.
✗
Create a placement group and launch the instance in it
Why it's wrong here
A placement group only controls the physical placement of instances—cluster for low latency, spread for isolation, or partition for fault-tolerant big data applications. It does not perform health checks, nor does it have any mechanism to replace failed instances. Even if you place the instance in a spread placement group to minimize correlated failures, you must still separately create an ASG or use EC2 Auto Recovery to actually replace the instance after a failure.
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Place the instance behind an Elastic Load Balancer
Why it's wrong here
Placing the instance behind an Elastic Load Balancer enables the ELB to route traffic to the instance and health-check its status. However, an ELB is strictly a traffic distribution service—it does not have the ability to terminate or launch EC2 instances. If the instance fails, the ELB will simply stop sending traffic to that unhealthy target, but the instance remains down and the application stays unavailable unless another service such as an Auto Scaling group is configured to replace it.
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Configure an Amazon Route 53 health check with failover routing
Why it's wrong here
Amazon Route 53 health checks with failover routing policy can monitor the instance's endpoint and, if it fails, remove the failed record and respond to DNS queries with a healthy endpoint. This requires you to define at least one other record or resource as a failover target, but Route 53 cannot provision or start EC2 instances. Thus, this approach only reroutes client traffic; it does nothing to bring the original critical instance back to a running state.

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SOA-C02 Reliability and Business Continuity Practice Question

Why each option matters

Option-by-option breakdown

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