Connection draining (for CLB) and deregistration delay (for ALB/NLB) is a feature that allows the load balancer to stop sending new requests to a target that is deregistering or marked unhealthy, while still completing in-flight requests for a configurable timeout period [citation:6][citation:10].
Connection draining (for Classic Load Balancers) and deregistration delay (for Application and Network Load Balancers) is a feature that ensures a target is gracefully removed from service. When a target is marked for deregistration or becomes unhealthy, the load balancer immediately stops sending new requests to it. However, it continues to allow any in-flight requests that are already in progress to complete within a configurable timeout period. This prevents a hard cutover from interrupting active user sessions [citation:6][citation:10].