A company is migrating a legacy application to AWS. The application runs on EC2 instances across multiple Availability Zones behind an Application Load Balancer (ALB). The target group routing…

The Least Outstanding Requests (LOR) algorithm is fully compatible with sticky sessions on an ALB target group. When sticky sessions are enabled, LOR ensures that new requests from a user without an existing session cookie are routed to the instance with the fewest outstanding requests, while existing sessions continue to route to the same target - eliminating the routing conflicts that cause application errors under weighted random with stickiness enabled.

Anomaly mitigation helps identify and stop routing to misbehaving targets, but it does not resolve the algorithmic incompatibility between weighted random routing and sticky sessions that is causing the application errors.

Turning off cross-zone load balancing restricts traffic to targets within the same Availability Zone as the load balancer node, but does not address the root cause of session affinity conflicts introduced by the weighted random routing algorithm.

Increasing the deregistration delay extends the time a deregistering target continues to receive in-flight requests, which is relevant during scale-in or deployments, but has no effect on the routing algorithm incompatibility with sticky sessions causing current user errors.