AWS Certified Advanced Networking – Specialty (ANS-C00) — Question 347

A company uses an Application Load Balancer (ALB) to provide access to a multi-tenant web application for 25 customers. The company creates a unique hostname for each customer to use to access the application. Hostnames use the format customer-name.example.com.
Each customer has a dedicated group of Amazon EC2 instances that run their own version of the web application. When a customer visits customer- name.example.com, the ALB should route the request to the correct group of EC2 instances. The company requires a highly available solution that is easy to maintain.
Which solution meets these requirements at the LOWEST cost?

Answer options

• A. Create one ALB for all customers. Create a listener rule that includes an HTTP header condition to match the URL. Add a forward action to route the request to the customer target group. Use Amazon Route 53 to create an alias record for each customer-name.example.com hostname that points to the ALB.
• B. Create one ALB for each customer. Configure the listener to route requests to the customer target group. Configure an NGINX proxy server to manage connections to each ALB. Use Amazon Route 53 to create a CNAME record for each customer-name.example.com hostname that points to the NGINX proxy server.
• C. Create one ALB for all customers. Create a listener rule that includes a Host header condition to match the hostname. Add a forward action to route the request to the customer target group. Use Amazon Route 53 to create an alias record for each customer-name.example.com hostname that points to the ALB.
• D. Create one ALB for each customer. Configure the listener to route requests to the customer target group. Create an Amazon CloudFront distribution. Add each ALB to the distribution as a custom origin. Use Amazon Route 53 to create an alias for each customer-name.example.com hostname that points to the CloudFront distribution.

Correct answer: C

Explanation

Using a single ALB with Host header routing is the most cost-effective and highly available solution because it eliminates the overhead and cost of running 25 separate load balancers. Routing based on the Host header correctly identifies the requested customer domain (customer-name.example.com) to forward traffic to the appropriate target group. Options B and D are excessively expensive and complex due to provisioning multiple ALBs, while Option A incorrectly uses an HTTP header condition instead of a Host header condition to match the domain.