Cluster capacity

You can provide capacity to an Amazon ECS cluster in several ways. For example, you can launch Amazon EC2 instances and register them with the cluster at start-up using the Amazon ECS container agent. However, this method can be challenging because you need to manage scaling on your own. Therefore, we recommend that you use Amazon ECS capacity providers. They manage resource scaling for you. There are three kinds of capacity providers: Amazon EC2, Fargate, and Fargate Spot. For more information about Amazon ECS capacity providers, see Amazon ECS capacity providers in the Amazon Elastic Container Service Developer Guide.

The Fargate and Fargate Spot capacity providers handle the lifecycle of Fargate tasks for you. Fargate provides on-demand capacity, and Fargate Spot provides Spot capacity. When a task is launched, ECS provisions a Fargate resource for you. This Fargate resource comes with the memory and CPU units that directly correspond to the task-level limits that you declared in your task definition. Each task receives its own Fargate resource, making a 1:1 relationship between the task and compute resources.

Tasks that run on Fargate Spot are subject to interruption. Interruptions come after a two-minute warning. These occur during periods of heavy demand. Fargate Spot works best for interruption-tolerant workloads such as batch jobs, development or staging environments. They're also suitable for any other scenario where high availability and low latency isn't a requirement.

You can run Fargate Spot tasks alongside Fargate on-demand tasks. By using them together, you receive provision “burst” capacity at a lower cost.

ECS can also manage the Amazon EC2 instance capacity for your tasks. Each Amazon EC2 Capacity Provider is associated with an Amazon EC2 Auto Scaling Group that you specify. When you use the Amazon EC2 Capacity Provider, ECS cluster auto scaling maintains the size of the Amazon EC2 Auto Scaling Group to ensure all scheduled tasks can be placed.