Stateful applications require session persistence to ensure that subsequent requests from the same user are routed to the same backend instance. When CloudFront is used in front of an ALB, session-related cookies must be forwarded correctly; otherwise, CloudFront can route requests to different targets, causing session loss and random logouts.
Configuring cookie forwarding in the CloudFront cache behavior ensures that session cookies (such as authentication tokens) are forwarded to the ALB and not stripped or cached incorrectly. Without this configuration, CloudFront may serve cached responses that do not align with the user’s active session state, leading to authentication issues.
On the ALB side, sticky sessions (session affinity) must be enabled on the target group to ensure that requests with the same session cookie are consistently routed to the same EC2 instance. ALB stickiness uses application cookies to bind a user session to a specific target, which is critical for stateful applications that store session data in memory.
Option A affects load distribution efficiency but does not address session persistence. Option C (header forwarding) is unnecessary unless the application explicitly stores session state in headers, which is uncommon. Option D applies only when using multiple target groups and listener rules, which is not the case here.
Together, enabling cookie forwarding in CloudFront and sticky sessions at the ALB target group resolves the logout issue by maintaining consistent session routing from the user through CloudFront to the same backend instance.
