A company deploys a new web application on Amazon EC2 instances. The application runs in private subnets in three Availability Zones behind an…

The user's issue, where every new web request restarts the login process, indicates a loss of session state. In a load-balanced environment with multiple backend instances, this happens when subsequent requests from the same user are routed to different instances, each unaware of the session created on another. The solution is to enable session affinity, or "sticky sessions," on the Application Load Balancer (ALB). This feature uses cookies to ensure that all requests from a specific user during a session are consistently sent to the same target EC2 instance, thereby preserving session state. This is configured at the target group level.

A. Stickiness is an attribute of the target group, which manages the collection of targets (EC2 instances). It is not configured in the ALB's listener rules, which route traffic based on path or host.

B. Replacing an ALB with a Network Load Balancer (NLB) is an inappropriate architectural change. ALBs operate at Layer 7 and are designed to handle HTTP/HTTPS traffic and cookies, making them ideal for this scenario.

D. Removing the ALB and using Route 53 failover is incorrect. This would eliminate the load balancing and high availability benefits across instances and would not solve the core session affinity problem.

1. AWS Documentation, Elastic Load Balancing User Guide: "Sticky sessions are a mechanism to route requests from the same client to the same target. Elastic Load Balancing uses cookies to enable sticky sessions. Stickiness is configured at the target group level." (Source: Elastic Load Balancing User Guide, section on "Sticky sessions for your Application Load Balancer").

2. AWS Documentation, Elastic Load Balancing User Guide: "You enable or disable sticky sessions at the target group level... You can use application-based stickiness to maintain affinity based on a cookie generated by your application." (Source: Elastic Load Balancing User Guide, section on "Target group attributes", specifically the stickiness.type and stickiness.appcookie.cookiename attributes).

3. AWS Documentation, Elastic Load Balancing User Guide: "A listener is a process that checks for connection requests, using the protocol and port that you configure. The rules that you define for a listener determine how the load balancer routes requests to its registered targets." (Source: Elastic Load Balancing User Guide, section on "Listeners for your Application Load Balancers". This confirms stickiness is not a listener rule setting).