When a load balancer implements this policy, the load balancer uses a special cookie to track the instance for each request. When the load balancer receives a request, it first checks to see if this cookie is present in the request. If so, the load balancer sends the request to the application server specified in the cookie. If not, the load balancer sends the request to a server that is chosen based on the existing load-balancing algorithm.
A cookie is inserted into the response for binding subsequent requests from the same user to that server. The validity of the cookie is based on the cookie expiration time, which is specified in the policy configuration.
For more information, see Duration-Based Session Stickiness in the Classic Load Balancers Guide.