A company runs its core business logic on a fleet of Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer (ALB). Route 53 record api.example.com points to the ALB. The development team must deploy a major update to the business logic such that during a testing window only 10% of customers receive the new version, and each customer must consistently use the same version for the duration of the testing window. How should the company deploy the update to satisfy these requirements?

The correct solution leverages an Application Load Balancer's (ALB) weighted target group routing and stickiness features. By creating a new target group for the updated business logic and configuring the ALB listener to distribute 10% of traffic to it, the company can achieve the desired traffic split. Enabling target-group stickiness ensures that once a customer is routed to a specific version (either old or new), subsequent requests from that customer are consistently directed to the same version, fulfilling the requirement for consistent customer experience during the testing window. Option 1 is incorrect because using two ALBs with Route 53 weighted routing would distribute traffic at the DNS level, which does not guarantee session stickiness for individual customers to a specific application version. Option 3 describes a rolling update strategy for an Auto Scaling group, which would gradually replace all instances with the new version, not split traffic or maintain stickiness for a testing window. Option 4 is incorrect because changing the ALB routing algorithm to least outstanding requests (LOR) doesn't achieve weighted routing, and while ALB session stickiness is enabled, the traffic split is not controlled as required.