SOA-C02 Networking and Content Delivery Practice Question

A company is using an Application Load Balancer (ALB) to distribute traffic to a fleet of EC2 instances. The company needs to ensure that the ALB sends requests to instances that are healthy and can serve traffic. Which feature should be used to monitor the health of the instances?

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

✓

Health checks

Health checks allow the ALB to monitor the health of EC2 instances by sending periodic requests to a specified endpoint (e.g., /health). If an instance fails consecutive health checks, the ALB stops sending traffic to it. Option B is incorrect because sticky sessions (session affinity) ensure a client's requests are sent to the same instance, not health monitoring. Option C is incorrect because cross-zone load balancing distributes traffic across instances in multiple Availability Zones. Option D is incorrect because connection draining (deregistration delay) allows in-flight requests to complete before an instance is removed from the target group.

Answer analysis

Option-by-option breakdown

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

✓
Health checks
Why this is correct
Health checks in an Application Load Balancer (ALB) are the mechanism that actively monitors the availability of targets by sending HTTP or HTTPS requests to a specified path, such as /health, and evaluating the response against configured success codes, e.g., 200. If a target fails a consecutive number of checks, the ALB marks it unhealthy and stops routing new traffic to it, while healthy targets continue to receive requests. This is the core feature that enables the ALB to perform automatic failover and maintain high availability.
✗
Sticky sessions
Why it's wrong here
Sticky sessions, also known as session affinity, use a cookie generated by the ALB or the application to bind a client's entire session to a specific target for the duration of a configured cookie lifetime. While this can be useful for stateful applications, it does not perform any health monitoring; a target could be marked unhealthy based on health checks, but sticky sessions themselves do not detect failures or probe instance status. They simply influence traffic routing based on client identity, not on target health.
✗
Cross-zone load balancing
Why it's wrong here
Cross-zone load balancing is a feature that enables the ALB to distribute incoming traffic evenly across all registered targets in all enabled Availability Zones, rather than keeping traffic confined to the zone where the client request originated. This setting improves overall utilization and latency by spreading load, but it does not assess the health or condition of the targets; it operates purely on load distribution and has no awareness of whether an instance is failing or has become unreachable.
✗
Connection draining
Why it's wrong here
Connection draining, also called deregistration delay, is a process that allows in-flight requests to complete on a target that is being deregistered or marked unhealthy before the target is actually removed from the target group. It gives existing connections a grace period to finish, preventing abrupt disconnects, but it does not proactively monitor health or detect failures. Instead, it is a cleanup mechanism that operates after an instance has already been marked unhealthy or is intentionally being taken out of rotation.

Go deeper

SOA-C02 Networking and Content Delivery Practice Question

Why each option matters

Option-by-option breakdown

Related to this question