Require tasks to be deployed to hosts that match the given Cluster Query Language expression. See http://docs.aws.amazon.com/AmazonECS/latest/developerguide/cluster-query-language.html for details on the Cluster Query Language.
fun (String) -> PlacementConstraint
Require tasks to be deployed to separate hosts.
Predefined list of constraints that require each task to be deployed on a separate host.