Retrieve ecs resources for serverless policies or related resources

        Requires arns in new format.
        https://docs.aws.amazon.com/AmazonECS/latest/userguide/ecs-resource-ids.html

def get_resources(self, ids, cache=True):
        """Retrieve ecs resources for serverless policies or related resources

        Requires arns in new format.
        https://docs.aws.amazon.com/AmazonECS/latest/userguide/ecs-resource-ids.html
        """
        cluster_resources = {}
        for i in ids:
            _, ident = i.rsplit(':', 1)
            parts = ident.split('/', 2)
            if len(parts) != 3:
                raise PolicyExecutionError("New format ecs arn required")
            cluster_resources.setdefault(parts[1], []).append(parts[2])

        results = []
        client = local_session(self.manager.session_factory).client('ecs')
        for cid, resource_ids in cluster_resources.items():
            results.extend(
                self.process_cluster_resources(client, cid, resource_ids))
        return results