Capacity creation

If you use AWS Fargate, AWS manages your capacity.

An Amazon ECS container instance is an Amazon EC2 instance that is running the Amazon ECS container agent and has been registered into an Amazon ECS cluster. When you run tasks with Amazon ECS using the EC2 launch type, External launch type or an Auto Scaling group capacity provider, your tasks are placed on your active container instances. You are responsible for the container instance management and maintenance.

Amazon ECS provides Amazon ECS-optimized AMIs (for both Linux and Windows) which contain the software required to run your tasks. All software is tested before the AMIs are released.

Container instance concepts

• Your container instance must be running the Amazon ECS container agent. The container agent is able to register the instance into one of your clusters. If you use an Amazon ECS-optimized AMI, the agent is already installed. To use a different operating system, install the agent. For more information, see Updating the Amazon ECS container agent.

• Because the Amazon ECS container agent makes calls to Amazon ECS on your behalf, you must launch container instances with an IAM role that authenticates to your account and provides the required resource permissions. For more information, see Amazon ECS container instance IAM role.

• The Linux Amazon ECS-optimized AMI version 20200430 and later support the Amazon EC2 Instance Metadata Service Version 2 (IMDSv2) on your container instances. Amazon ECS-optimized AMIs versions prior to 20200430 support Amazon EC2 Instance Metadata Service Version 1 (IMDSv1). For more information, see Configuring the instance metadata service in the Amazon EC2 User Guide for Linux Instances.

• If any of the containers associated with your tasks require external connectivity, you can map their network ports to ports on the host Amazon ECS container instance so they are reachable from the internet. Your container instance security group must allow inbound access to the ports you want to expose. For more information, see Create a Security Group in the Amazon VPC Getting Started Guide.

• We recommend launching your container instances inside a VPC, because Amazon VPC delivers more control over your network and offers more extensive configuration capabilities. For more information, see Amazon EC2 and Amazon Virtual Private Cloud in the Amazon EC2 User Guide for Linux Instances.

• Container instances need access to communicate with the Amazon ECS service endpoint. This can be through an interface VPC endpoint or through your container instances having public IP addresses.

  For more information about interface VPC endpoints, see Amazon ECS interface VPC endpoints (AWS PrivateLink).

  If you do not have an interface VPC endpoint configured and your container instances do not have public IP addresses, then they must use network address translation (NAT) to provide this access. For more information, see NAT gateways in the Amazon VPC User Guide and HTTP proxy configuration for Linux container instances in this guide. For more information, see Create a virtual private cloud.

• The following rules apply because each container instance has unique state information that is stored locally on the container instance and within Amazon ECS:

  • You should not deregister an instance from one cluster and re-register it into another. To relocate container instance resources, we recommend that you terminate container instances from one cluster and launch new container instances with the latest Amazon ECS-optimized Amazon Linux 2 AMI in the new cluster. For more information, see Terminate Your Instance in the Amazon EC2 User Guide for Linux Instances and Launching an Amazon ECS Linux container instance.

  • You cannot stop a container instance and change its instance type. Instead, we recommend that you terminate the container instance and launch a new container instance with the desired instance size and the latest Amazon ECS-optimized Amazon Linux 2 AMI in your desired cluster. For more information, see Terminate Your Instance in the Amazon EC2 User Guide for Linux Instances and Launching an Amazon ECS Linux container instance in this guide.

Choosing the Amazon EC2 instance type

To determine which instance types you can use, start by eliminating the instance types or instance families that don't meet the specific requirements of your application. For example, if your application requires a GPU, you can exclude any instance types that don't have a GPU. However, you should also consider other requirements, too. For example, consider the CPU architecture, network throughput, and if instance storage is a requirement. Next, examine the amount of CPU and memory provided by each instance type. As a general rule, the CPU and memory must be large enough to hold at least one replica of the task that you want to run.

You can choose from the instance types that are compatible with your application. With larger instances, you can launch more tasks at the same time. And, with smaller instances, you can scale out in a more fine-grained way to save costs. You don't need to choose a single Amazon EC2 instance type that to fit all the applications in your cluster. Instead, you can create multiple Auto Scaling Groups,. Each group can have a different instance type. Then, you can create an Amazon EC2 Capacity Provider for each one of these groups. Last, in the Capacity Provider strategy of your service and task, you can select the Capacity Provider that best suits its needs. For more information, see Amazon EC2 Instances.

Using Amazon EC2 Spot

Spot capacity can provide significant cost savings over on-demand instances. Spot capacity is excess capacity that's priced significantly lower than on-demand or reserved capacity. Spot capacity is suitable for batch processing and machine-learning workloads, and development and staging environments. More generally, it's suitable for any workload that tolerates temporary downtime.

Understand that the following consequences because Spot capacity might not be available all the time.

• During periods of extremely high demand, Spot capacity might be unavailable. This can cause Amazon EC2 Spot instance launches to be delayed. In these events, Amazon ECS services retry launching tasks, and Amazon EC2 Auto Scaling groups also retry launching instances, until the required capacity becomes available. Amazon EC2 doesn't replace Spot capacity with on-demand capacity.

• When the overall demand for capacity increases, Spot instances and tasks might be terminated with only a two-minute warning. After the warning is sent, tasks should begin an orderly shutdown if necessary before the instance is fully terminated. This helps minimize the possibility of errors. For more information about a graceful shutdown, see Graceful shutdowns with ECS .

To help minimize Spot capacity shortages, consider the following recommendations:

• Use multiple Regions and Availability Zones - Spot capacity varies by Region and Availability Zone. You can improve Spot availability by running your workloads in multiple Regions and Availability Zones. If possible, specify subnets in all the Availability Zones in the Regions where you run your tasks and instances.

• Use multiple Amazon EC2 instance types - When you use Mixed Instance Policies with Amazon EC2 Auto Scaling, multiple instance types are launched into your Auto Scaling Group. This ensures that a request for Spot capacity can be fulfilled when needed. To maximize reliability and minimize complexity, use instance types with roughly the same amount of CPU and memory in your Mixed Instances Policy. These instances can be from a different generation, or variants of the same base instance type. Note that they might come with additional features that you might not require. An example of such a list could include m4.large, m5.large, m5a.large, m5d.large, m5n.large, m5dn.large, and m5ad.large. For more information, see Auto Scaling groups with multiple instance types and purchase options in the Amazon EC2 Auto Scaling User Guide.

• Use the capacity-optimized Spot allocation strategy - With Amazon EC2 Spot, you can choose between the capacity- and cost-optimized allocation strategies. If you choose the capacity-optimized strategy when launching a new instance, Amazon EC2 Spot selects the instance type with the greatest availability in the selected Availability Zone. This helps reduce the possibility that the instance is terminated soon after it launches.