Cluster

A Cluster is a logical grouping of resources used by ECS to manage and run containerized applications. A cluster is essentially a pool of computing resources (e.g., EC2 instances or Fargate) where your tasks (containers) run.

• EC2 Cluster: When you use EC2 launch type, the cluster contains EC2 instances that are registered to ECS.
• Fargate Cluster: When you use Fargate, the cluster is virtualized, and ECS manages the infrastructure for you (you don't manage the underlying EC2 instances).

Task

A Task is a running instance of a containerized application in ECS. It's the basic unit of work in ECS. A task is defined by a Task Definition, which specifies the Docker image to use, resource requirements (like CPU and memory), networking configurations, environment variables, and more.

• Task Definition (similar to launch templates): The blueprint for your task, describing which containers to run, their configuration, and the resources they need.
• Running Task: Once ECS launches a task from a task definition, it becomes a running task, executing your containerized application.

Service

A Service is a higher-level abstraction on top of tasks in ECS. A service allows you to maintain and scale a specified number of task instances running and ensures that the desired number of tasks are continuously running.

• Scaling: Services allow automatic scaling of tasks up or down based on demand (e.g., adding more task instances when traffic increases).
• Load Balancing: ECS services can also be associated with a load balancer (like an ELB) to distribute incoming traffic across running tasks.