Amazon ECS capacity providers for the EC2 launch type - Amazon Elastic Container Service

Amazon ECS capacity providers for the EC2 launch type

When you use Amazon EC2 instances for your capacity, you use Auto Scaling groups to manage the Amazon EC2 instances registered to their clusters. Auto Scaling helps ensure that you have the correct number of Amazon EC2 instances available to handle the application load.

You can use the managed scaling feature to have Amazon ECS manage the scale-in and scale-out actions of the Auto Scaling group, or you can manage the scaling actions yourself. For more information, see Automatically manage Amazon ECS capacity with cluster auto scaling.

We recommend that you create a new empty Auto Scaling group. If you use an existing Auto Scaling group, any Amazon EC2 instances that are associated with the group that were already running and registered to an Amazon ECS cluster before the Auto Scaling group being used to create a capacity provider might not be properly registered with the capacity provider. This might cause issues when using the capacity provider in a capacity provider strategy. Use DescribeContainerInstances to confirm whether a container instance is associated with a capacity provider or not.


To create an empty Auto Scaling group, set the desired count to zero. After you created the capacity provider and associated it with a cluster, you can then scale it out.

When you use the Amazon ECS console, Amazon ECS creates an Amazon EC2 launch template and Auto Scaling group on your behalf as part of the AWS CloudFormation stack. They are prefixed with EC2ContainerService-<ClusterName>. You can use the Auto Scaling group as a capacity provider for that cluster.

We recommend you use managed instance draining to allow for graceful termination of Amazon EC2 instances that won't disrupt your workloads. This feature is on by default. For more information, see Safely stop Amazon ECS workloads running on EC2 instances

Consider the following when using Auto Scaling group capacity providers in the console:

  • An Auto Scaling group must have a MaxSize greater than zero to scale out.

  • The Auto Scaling group can't have instance weighting settings.

  • If the Auto Scaling group can't scale out to accommodate the number of tasks run, the tasks fails to transition beyond the PROVISIONING state.

  • Don't modify the scaling policy resource associated with your Auto Scaling groups that are managed by capacity providers.

  • If managed scaling is turned on when you create a capacity provider, the Auto Scaling group desired count can be set to 0. When managed scaling is turned on, Amazon ECS manages the scale-in and scale-out actions of the Auto Scaling group.

  • You must associate capacity provider with a cluster before you associate it with the capacity provider strategy.

  • You can specify a maximum of 20 capacity providers for a capacity provider strategy.

  • You can't update a service using an Auto Scaling group capacity provider to use a Fargate capacity provider. The opposite is also the case.

  • In a capacity provider strategy, if no weight value is specified for a capacity provider in the console, then the default value of 1 is used. If using the API or AWS CLI, the default value of 0 is used.

  • When multiple capacity providers are specified within a capacity provider strategy, at least one of the capacity providers must have a weight value that's greater than zero. Any capacity providers with a weight of zero aren't used to place tasks. If you specify multiple capacity providers in a strategy with all the same weight of zero, then any RunTask or CreateService actions using the capacity provider strategy fail.

  • In a capacity provider strategy, only one capacity provider can have a defined base value. If no base value is specified, the default value of zero is used.

  • A cluster can contain a mix of both Auto Scaling group capacity providers and Fargate capacity providers. However, a capacity provider strategy can only contain Auto Scaling group or Fargate capacity providers, but not both.

  • A cluster can contain a mix of services and standalone tasks that use both capacity providers and launch types. A service can be updated to use a capacity provider strategy rather than a launch type. However, you must force a new deployment when doing so.

  • Amazon ECS supports Amazon EC2 Auto Scaling warm pools. A warm pool is a group of pre-initialized Amazon EC2 instances ready to be placed into service. Whenever your application needs to scale out, Amazon EC2 Auto Scaling uses the pre-initialized instances from the warm pool rather than launching cold instances. This allows for any final initialization process to run before the instance is placed into service. For more information, see Configuring pre-initialized instances for your Amazon ECS Auto Scaling group.

For more information about creating an Amazon EC2 Auto Scaling launch template, see Launch Templates in the Amazon EC2 Auto Scaling User Guide. For more information about creating an Amazon EC2 Auto Scaling group, see Auto Scaling groups in the Amazon EC2 Auto Scaling User Guide.