Final answer:
In Amazon ECS, scaling and HA for containers are managed through the Service definition, which sets the desired number of task instances and handles placement and scaling.
Step-by-step explanation:
To configure scaling and high availability (HA) for containers in Amazon Elastic Container Service (ECS), you would primarily use the Service definition. The Service allows you to specify the desired number of simultaneous instances of a task definition, handles task placement strategies, and deals with task scaling. The Cluster is the logical grouping of tasks or services. While the Tasks define individual applications, they are not responsible for scaling or HA, which are managed at the service level.