Amazon ECS supports in Preview updating Placement Strategy and Constraints for existing ECS Services
Amazon Elastic Container Service (ECS) now supports updating Placement Strategy and Constraints for existing ECS services (in Preview). ECS customers can now update the placement strategies and constraints for their ECS services without having to recreate a service with the desired changes. This flexibility and control in managing the placement of service tasks helps customers save cost and reduce potential service downtime.
Source:: Amazon AWS