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ELB Health Checks

5 minutes 5 Questions

Health checks in Elastic Load Balancing are a feature that continuously monitors the health of the registered instances, marking them as healthy or unhealthy based on predefined criteria. They are used to determine which instances can receive traffic from the load balancer. Health checks are config…

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AWS Certified Solutions Architect - ELB Health Checks Example Questions

Test your knowledge of ELB Health Checks

Question 1

An AWS Network Load Balancer distributes traffic to a fleet of EC2 instances running an HTTP web application. The application must maintain stable performance during rapid workload changes. Which health check configuration provides the most reliable application-level health detection while avoiding unnecessary flapping or added load?

Correct Answer: Configure an HTTP HealthCheck and adjust the interval and thresholds depending on the workload.

For an HTTP-based application behind an AWS Network Load Balancer, an HTTP health check validates end-to-end application readiness by requesting a specific path and evaluating the response code. This prevents routing traffic to instances where the port is open but the app is unhealthy. Tuning the health check interval and healthy/unhealthy thresholds to the workload balances fast failure detection with stability: overly aggressive settings (short interval, low thresholds) increase load and risk flapping, while overly lax settings delay failover. TCP-only checks lack application-level validation, and UDP health checks are not appropriate for HTTP apps and are generally not supported as a UDP protocol health check on NLB.

Question 2

A web application with an ELB receives sudden spikes of traffic. Users report slow performance during these spikes. You've been asked to improve the health checks so unhealthy instances are quickly removed from the ELB. What is the best configuration change you can make?

Correct Answer: Decrease the HealthCheck interval and lower the UnhealthyThreshold.

By decreasing the HealthCheck interval and lowering the UnhealthyThreshold, ELB will perform health checks more frequently and remove unhealthy instances from service more quickly, ensuring better performance during traffic spikes.

Question 3

Your load balancer performs TCP health checks and allows you to configure two parameters: Interval (how often a health check runs) and HealthyThreshold (the number of consecutive successful checks required before a target is marked healthy). Under peak load, targets experience brief, intermittent failures that cause health status to flap, and some client connections fail when traffic is sent to targets that have only momentarily recovered. Without changing target capacity, which configuration best reduces flapping and health-check overhead while ensuring targets are returned to service only after a sustained recovery?

Correct Answer: Increase the HealthCheck interval and increase the HealthyThreshold.

Increasing the health check interval reduces the frequency of TCP probes, lowering overhead on targets and decreasing the chance that transient blips trigger status changes. Increasing the HealthyThreshold requires more consecutive successful checks before a target is returned to service, which prevents briefly recovering targets from being marked healthy too quickly. Together, these changes reduce health status flapping and minimize user-facing failed connections caused by routing traffic to targets that have not yet stabilized.

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