AWS Certified Solutions Architect – Professional — Question 802

You are responsible for a web application that consists of an Elastic Load Balancing (ELB) load balancer in front of an Auto Scaling group of Amazon Elastic
Compute Cloud (EC2) instances. For a recent deployment of a new version of the application, a new Amazon Machine Image (AMI) was created, and the Auto
Scaling group was updated with a new launch configuration that refers to this new AMI. During the deployment, you received complaints from users that the website was responding with errors. All instances passed the ELB health checks.
What should you do in order to avoid errors for future deployments? (Choose two.)

Answer options

• A. Add an Elastic Load Balancing health check to the Auto Scaling group. Set a short period for the health checks to operate as soon as possible in order to prevent premature registration of the instance to the load balancer.
• B. Enable EC2 instance CloudWatch alerts to change the launch configuration's AMI to the previous one. Gradually terminate instances that are using the new AMI.
• C. Set the Elastic Load Balancing health check configuration to target a part of the application that fully tests application health and returns an error if the tests fail.
• D. Create a new launch configuration that refers to the new AMI, and associate it with the group. Double the size of the group, wait for the new instances to become healthy, and reduce back to the original size. If new instances do not become healthy, associate the previous launch configuration.
• E. Increase the Elastic Load Balancing Unhealthy Threshold to a higher value to prevent an unhealthy instance from going into service behind the load balancer.

Correct answer: C, D

Explanation

Option C is correct because standard TCP or simple HTTP health checks might pass even if the application itself is failing internally; targeting a deep application health endpoint ensures the app is fully functional before serving traffic. Option D is correct because performing a blue/green-style deployment by doubling the capacity allows validation of the new instances before removing the old ones, offering an easy rollback path. Other options fail because a short grace period (A) can cause premature terminations, and increasing the unhealthy threshold (E) actually delays the detection of bad instances.