Increasing Amazon ECS Linux container instance network interfaces

Note

This feature is not available on Fargate.

Each task that uses the awsvpc network mode receives its own elastic network interface (ENI), which is attached to the container instance that hosts it. There is a default limit to the number of network interfaces that can be attached to an Amazon EC2 instance, and the primary network interface counts as one. For example, by default a c5.large instance may have up to three ENIs attached to it. The primary network interface for the instance counts as one, so you can attach an additional two ENIs to the instance. Because each task using the awsvpc network mode requires an ENI, you can typically only run two such tasks on this instance type.

Amazon ECS supports launching container instances with increased ENI density using supported Amazon EC2 instance types. When you use these instance types and turn on the awsvpcTrunking account setting, additional ENIs are available on newly launched container instances. This configuration allows you to place more tasks on each container instance. To use the console to turn on the feature, see Modifying Amazon ECS account settings. To use the AWS CLI to turn on the feature, see Managing Amazon ECS account settings using the AWS CLI.

For example, a c5.large instance with awsvpcTrunking has an increased ENI limit of twelve. The container instance will have the primary network interface and Amazon ECS creates and attaches a "trunk" network interface to the container instance. So this configuration allows you to launch ten tasks on the container instance instead of the current two tasks.

The trunk network interface is fully managed by Amazon ECS and is deleted when you either terminate or deregister your container instance from the cluster. For more information, see Amazon ECS task networking options for the EC2 launch type.

Considerations

Consider the following when using the ENI trunking feature.

Only Linux variants of the Amazon ECS-optimized AMI, or other Amazon Linux variants with version 1.28.1 or later of the container agent and version 1.28.1-2 or later of the ecs-init package, support the increased ENI limits. If you use the latest Linux variant of the Amazon ECS-optimized AMI, these requirements will be met. Windows containers are not supported at this time.
Only new Amazon EC2 instances launched after enabling awsvpcTrunking receive the increased ENI limits and the trunk network interface. Previously launched instances do not receive these features regardless of the actions taken.
Amazon EC2 instances must have resource-based IPv4 DNS requests turned off. To disable this option, clear the Enable resource-based IPV4 (A record) DNS requests option when you create a new instance in the Amazon EC2 console. To disable this option using the AWS CLI, use the following command.
```
aws ec2 modify-private-dns-name-options --instance-id i-xxxxxxx --no-enable-resource-name-dns-a-record --no-dry-run
```
Amazon EC2 instances in shared subnets are not supported. They will fail to register to a cluster if they are used.
Your tasks must use the awsvpc network mode and the EC2 launch type. Tasks using the Fargate launch type always received a dedicated ENI regardless of how many are launched, so this feature is not needed.
Your tasks must be launched in the same Amazon VPC as your container instance. Your tasks will fail to start with an attribute error if they are not within the same VPC.
When launching a new container instance, the instance transitions to a REGISTERING status while the trunk elastic network interface is provisioned for the instance. If the registration fails, the instance transitions to a REGISTRATION_FAILED status. You can troubleshoot a failed registration by describing the container instance to view the statusReason field which describes the reason for the failure. The container instance then can be manually deregistered or terminated. Once the container instance is successfully deregistered or terminated, Amazon ECS will delete the trunk ENI.

Note
Amazon ECS emits container instance state change events which you can monitor for instances that transition to a REGISTRATION_FAILED state. For more information, see Amazon ECS container instance state change events.
Once the container instance is terminated, the instance transitions to a DEREGISTERING status while the trunk elastic network interface is deprovisioned. The instance then transitions to an INACTIVE status.
If a container instance in a public subnet with the increased ENI limits is stopped and then restarted, the instance loses its public IP address, and the container agent loses its connection.
When you enable awsvpcTrunking, container instances receive an additional ENI that uses the VPC's default security group, and is managed by Amazon ECS.

A default VPC comes with a public subnet in each Availability Zone, an internet gateway, and settings to enable DNS resolution. The subnet is a public subnet, because the main route table sends the subnet's traffic that is destined for the internet to the internet gateway. You can make a default subnet into a private subnet by removing the route from the destination 0.0.0.0/0 to the internet gateway. However, if you do this, no container instance running in that subnet can access the internet. You can add or delete security group rules to control the traffic into and out of your subnets. For more information, see Security group rules in the Amazon Virtual Private Cloud User Guide.

Prerequisites

Before you launch a container instance with the increased ENI limits, the following prerequisites must be completed.

The service-linked role for Amazon ECS must be created. The Amazon ECS service-linked role provides Amazon ECS with the permissions to make calls to other AWS services on your behalf. This role is created for you automatically when you create a cluster, or if you create or update a service in the AWS Management Console. For more information, see Using service-linked roles for Amazon ECS. You can also create the service-linked role with the following AWS CLI command.
```
aws iam create-service-linked-role --aws-service-name ecs.amazonaws.com
```
Your account or container instance IAM role must enable the awsvpcTrunking account setting. We recommend that you create 2 container instance roles (ecsInstanceRole). You can then enable the awsvpcTrunking account setting for one role and use that role for tasks that require ENI trunking. For information about the container instance role, see Amazon ECS container instance IAM role.

After the prerequisites are met, you can launch a new container instance using one of the supported Amazon EC2 instance types, and the instance will have the increased ENI limits. For a list of supported instance types, see Supported instances for increased Amazon ECS container network interfaces. The container instance must have version 1.28.1 or later of the container agent and version 1.28.1-2 or later of the ecs-init package. If you use the latest Linux variant of the Amazon ECS-optimized AMI, these requirements will be met. For more information, see Launching an Amazon ECS Linux container instance.

Important

Amazon EC2 instances must have resource-based IPv4 DNS requests turned off. To disable this option, ensure the Enable resource-based IPV4 (A record) DNS requests option is deselected when creating a new instance using the Amazon EC2 console. To disable this option using the AWS CLI, use the following command.


aws ec2 modify-private-dns-name-options --instance-id i-xxxxxxx --no-enable-resource-name-dns-a-record --no-dry-run

To view your container instances with increased ENI limits with the AWS CLI

Each container instance has a default network interface, referred to as a trunk network interface. Use the following command to list your container instances with increased ENI limits by querying for the ecs.awsvpc-trunk-id attribute, which indicates it has a trunk network interface.

list-attributes (AWS CLI)


aws ecs list-attributes \
      --target-type container-instance \
      --attribute-name ecs.awsvpc-trunk-id \
      --cluster cluster_name \
      --region us-east-1

Get-ECSAttributeList (AWS Tools for Windows PowerShell)


Get-ECSAttributeList -TargetType container-instance -AttributeName ecs.awsvpc-trunk-id -Region us-east-1

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Document Conventions

Running a script when you launch a container instance

Supported EC2 instances