SAP-C02 Design for New Solutions Practice Question
A company runs a critical web application on EC2 instances in an Auto Scaling group across three Availability Zones. The application uses an Application Load Balancer (ALB) with a target group that has health checks configured. Recently, the operations team noticed that during a deployment, the ALB started routing traffic to a new instance before it was ready to serve requests, causing a brief period of errors. The team wants to ensure that new instances are fully initialized and ready before receiving traffic. The application takes about 30 seconds to start up. Current health check settings: health check protocol HTTP, path /, interval 30 seconds, timeout 5 seconds, healthy threshold 2, unhealthy threshold 2. The deployment uses the Auto Scaling group's instance refresh feature. Which of the following is the MOST effective way to prevent traffic from being sent to instances that are not ready?
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
✓
Implement a lifecycle hook in the Auto Scaling group that waits for the instance to signal readiness. Also, configure the target group health check with a longer interval and a higher healthy threshold to ensure the instance is fully operational.
It uses a lifecycle hook to pause the instance until it signals readiness (e.g., via a custom script that completes initialization), and then configures the target group health check with a longer interval and higher healthy threshold to ensure the instance is fully operational before receiving traffic. This prevents the ALB from routing traffic to an instance that is not yet ready. Option B is wrong because simply increasing the health check interval and threshold does not guarantee the instance has finished its startup process; it may still fail if the application is not ready when the first health check occurs (if the instance takes 30 seconds and interval is 60, the first check is at 60 seconds, but the threshold of 5 means it needs 5 consecutive successes, which delays traffic but doesn't ensure the instance is fully functional from the start). Option C is wrong because the instance refresh warm-up time only delays the start of the refresh process, not the time before an instance receives traffic; it does not integrate with application readiness. Option D is wrong because AWS Global Accelerator does not pre-warm endpoints; it provides static IP addresses and improves performance but does not handle application readiness checks.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Implement a lifecycle hook in the Auto Scaling group that waits for the instance to signal readiness. Also, configure the target group health check with a longer interval and a higher healthy threshold to ensure the instance is fully operational.
Why this is correct
Lifecycle hooks can pause the instance launch until the application signals that it is ready, and the health check can be tuned to match the startup time.
- ✗
Increase the health check interval to 60 seconds and the healthy threshold to 5.
Why it's wrong here
This delays the time until the instance is considered healthy but does not prevent the ALB from sending traffic if the health check passes earlier.
- ✗
Use the Auto Scaling group's instance refresh feature with a warm-up time of 60 seconds.
Why it's wrong here
Warm-up time in instance refresh specifies the time before the next batch of instances is terminated, not the time before an instance receives traffic.
- ✗
Use AWS Global Accelerator to pre-warm the endpoints before directing traffic.
Why it's wrong here
Global Accelerator does not have a pre-warming feature; it routes traffic to healthy endpoints.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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