placement constraints

 placement_constraints {
   type       = "memberOf"
   expression = "attribute:type == ${aws_instance.your_intance_name.private_dns}"
 }

See also

• Terraform resource: aws_ecs_service: launch_type (EC2, FARGATE), iam_role, depends_on, load_balancer, desired_count, placement_constraints, deployment_minimum_healthy_percent, iam role
• Amazon ECS, Service, Tasks (Task overview), capacity providers, Cluster Auto Scaling (CAS), aws ecs, ecs-cli, ~/.ecs/config, AWS Copilot, AWS Fargate, AWS CloudWatch Container Insights, /etc/ecs/ecs.config, Security group (SG), container agent, task definition, Amazon ECS events, best practices, Amazon ECS Exec Checker, Amazon ECS Agent, Service Connect, AWSServiceRoleForECS, Terraform ECS, AWS ECS Rolling deployments