AWS Certified Advanced Networking – Specialty (ANS-C01)Network DesignMedium
An e-commerce company experiences seasonal traffic spikes and needs to ensure its application remains highly available and performs optimally during peak loads. The application is deployed across multiple EC2 instances behind an Application Load Balancer (ALB) in an Auto Scaling group. The company wants to distribute incoming traffic evenly across healthy instances and scale capacity automatically. Which load balancing feature is crucial for achieving this distribution while handling variable traffic?
- AApplication Load Balancer (ALB) with weighted target groups
- BClassic Load Balancer (CLB) with sticky sessions
- CApplication Load Balancer (ALB) with round-robin routing and health checks
- DNetwork Load Balancer (NLB) with target groups
Show answer & explanationAnswer & explanation
Correct answer: C. Application Load Balancer (ALB) with round-robin routing and health checks
Application Load Balancers (ALB) distribute incoming application traffic across multiple targets, such as EC2 instances. With round-robin routing (default for ALBs) and continuous health checks on target groups, ALBs ensure that traffic is evenly distributed only to healthy instances, dynamically adapting to changes in instance availability and scaling.
Why the other options are wrong
- A. Weighted target groups are for routing different proportions of traffic to different groups, not primarily for even distribution across instances within a single group or handling scaling.
- B. CLB is a legacy service with fewer features and less flexibility than ALB, and sticky sessions are for session persistence, not for ensuring even distribution and scaling during peak loads.
- D. NLB operates at Layer 4, offering extreme performance but without application-layer features like path-based routing or advanced health checks, and is less suited for distributing HTTP/S traffic based on application needs.
ALB Round-Robin & Health Checks
Application Load Balancers (ALB) use round-robin distribution to send requests to healthy targets within a target group, ensuring even load distribution and high availability.
- Default distribution method for ALB
- Distributes traffic evenly across healthy targets
- Combined with health checks to avoid unhealthy instances
- Supports dynamic scaling of target instances
Memory trick: ALB's round-robin ensures every healthy instance gets a fair share.