Using IAM roles with Amazon ECS tasks - Amazon Elastic Container Service
Task execution roleAmazon EC2 container instance roleService-linked rolesRecommendations

Using IAM roles with Amazon ECS tasks

We recommend that you assign a task an IAM role. Its role can be distinguished from the role of the Amazon EC2 instance that it's running on. Assigning each task a role aligns with the principle of least privileged access and allows for greater granular control over actions and resources.

When assigning IAM roles for a task, you must use the following trust policy so that each of your tasks can assume an IAM role that's different from the one that your EC2 instance uses. This way, your task doesn't inherit the role of your EC2 instance.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "",
      "Effect": "Allow",
      "Principal": {
        "Service": "ecs-tasks.amazonaws.com"
      },
      "Action": "sts:AssumeRole"
    }
  ]
}

When you add a task role to a task definition, the Amazon ECS container agent automatically creates a token with a unique credential ID (for example, 12345678-90ab-cdef-1234-567890abcdef) for the task. This token and the role credentials are then added to the agent's internal cache. The agent populates the environment variable AWS_CONTAINER_CREDENTIALS_RELATIVE_URI in the container with the URI of the credential ID (for example, /v2/credentials/12345678-90ab-cdef-1234-567890abcdef).

This workflow shows the process involved when the Amazon ECS container agent caches credentials. These credentials are determined by the task role that is defined in the task definition.

You can manually retrieve the temporary role credentials from inside a container by appending the environment variable to the IP address of the Amazon ECS container agent and running the curl command on the resulting string.

curl 169.254.170.2$AWS_CONTAINER_CREDENTIALS_RELATIVE_URI

The expected output is as follows:

{
	"RoleArn": "arn:aws:iam::123456789012:role/SSMTaskRole-SSMFargateTaskIAMRole-DASWWSF2WGD6",
	"AccessKeyId": "AKIAIOSFODNN7EXAMPLE",
	"SecretAccessKey": "wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY",
	"Token": "IQoJb3JpZ2luX2VjEEM/Example==",
	"Expiration": "2021-01-16T00:51:53Z"
}

Newer versions of the AWS SDKs automatically fetch these credentials from the AWS_CONTAINER_CREDENTIALS_RELATIVE_URI environment variable when making AWS API calls.

The output includes an access key-pair consisting of a secret access key ID and a secret key which your application uses to access AWS resources. It also includes a token that AWS uses to verify that the credentials are valid. By default, credentials assigned to tasks using task roles are valid for six hours. After that, they are automatically rotated by the Amazon ECS container agent.

Task execution role

The task execution role is used to grant the Amazon ECS container agent permission to call specific AWS API actions on your behalf. For example, when you use AWS Fargate, Fargate needs an IAM role that allows it to pull images from Amazon ECR and write logs to CloudWatch Logs. An IAM role is also required when a task references a secret that's stored in AWS Secrets Manager, such as an image pull secret.

Note

If you're pulling images as an authenticated user, you're less likely to be impacted by the changes that occurred to Docker Hub's pull rate limits. For more information see, Private registry authentication for container instances.

By using Amazon ECR and Amazon ECR Public, you can avoid the limits imposed by Docker. If you pull images from Amazon ECR, this also helps shorten network pull times and reduces data transfer changes when traffic leaves your VPC.

Important

When you use Fargate, you must authenticate to a private image registry using repositoryCredentials. It's not possible to set the Amazon ECS container agent environment variables ECS_ENGINE_AUTH_TYPE or ECS_ENGINE_AUTH_DATA or modify the ecs.config file for tasks hosted on Fargate. For more information, see Private registry authentication for tasks.

Amazon EC2 container instance role

The Amazon ECS container agent is a container that runs on each Amazon EC2 instance in an Amazon ECS cluster. It's initialized outside of Amazon ECS using the init command that's available on the operating system. Consequently, it can't be granted permissions through a task role. Instead, the permissions have to be assigned to the Amazon EC2 instances that the agents run on. The actions list in the example AmazonEC2ContainerServiceforEC2Role policy need to be granted to the ecsInstanceRole. If you don't do this, your instances cannot join the cluster.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "ec2:DescribeTags",
                "ecs:CreateCluster",
                "ecs:DeregisterContainerInstance",
                "ecs:DiscoverPollEndpoint",
                "ecs:Poll",
                "ecs:RegisterContainerInstance",
                "ecs:StartTelemetrySession",
                "ecs:UpdateContainerInstancesState",
                "ecs:Submit*",
                "ecr:GetAuthorizationToken",
                "ecr:BatchCheckLayerAvailability",
                "ecr:GetDownloadUrlForLayer",
                "ecr:BatchGetImage",
                "logs:CreateLogStream",
                "logs:PutLogEvents"
            ],
            "Resource": "*"
        }
    ]
}

In this policy, the ecr and logs API actions allow the containers that are running on your instances to pull images from Amazon ECR and write logs to Amazon CloudWatch. The ecs actions allow the agent to register and de-register instances and to communicate with the Amazon ECS control plane. Of these, the ecs:CreateCluster action is optional.

Service-linked roles

You can use the service-linked role for Amazon ECS to grant the Amazon ECS service permission to call other service APIs on your behalf. Amazon ECS needs the permissions to create and delete network interfaces, register, and de-register targets with a target group. It also needs the necessary permissions to create and delete scaling policies. These permissions are granted through the service-linked role. This role is created on your behalf the first time that you use the service.

Note

If you inadvertently delete the service-linked role, you can recreate it. For instructions, see Create the service-linked role.

Recommendations

We recommend that you do the following when setting up your task IAM roles and policies.

Block access to Amazon EC2 metadata

When you run your tasks on Amazon EC2 instances, we strongly recommend that you block access to Amazon EC2 metadata to prevent your containers from inheriting the role assigned to those instances. If your applications have to call an AWS API action, use IAM roles for tasks instead.

To prevent tasks running in bridge mode from accessing Amazon EC2 metadata, run the following command or update the instance's user data. For more instruction on updating the user data of an instance, see this AWS Support Article. For more information about the task definition bridge mode, see task definition network mode.

sudo yum install -y iptables-services; sudo iptables --insert FORWARD 1 --in-interface docker+ --destination 192.0.2.0/32 --jump DROP

For this change to persist after a reboot, run the following command that's specific for your Amazon Machine Image (AMI):

  • Amazon Linux 2

    sudo iptables-save | sudo tee /etc/sysconfig/iptables && sudo systemctl enable --now iptables

  • Amazon Linux

    sudo service iptables save

For tasks that use awsvpc network mode, set the environment variable ECS_AWSVPC_BLOCK_IMDS to true in the /etc/ecs/ecs.config file.

You should set the ECS_ENABLE_TASK_IAM_ROLE_NETWORK_HOST variable to false in the ecs-agent config file to prevent the containers that are running within the host network from accessing the Amazon EC2 metadata.

Use awsvpc network mode

Use the network awsvpc network mode to restrict the flow of traffic between different tasks or between your tasks and other services that run within your Amazon VPC. This adds an additional layer of security. The awsvpc network mode provides task-level network isolation for tasks that run on Amazon EC2. It is the default mode on AWS Fargate. it's the only network mode that you can use to assign a security group to tasks.

Use IAM Access Advisor to refine roles

We recommend that you remove any actions that were never used or haven't been used for some time. This prevents unwanted access from happening. To do this, review the results produced by IAM Access Advisor, and then remove actions that were never used or haven't been used recently. You can do this by following the following steps.

Run the following command to generate a report showing the last access information for the referenced policy:

aws iam generate-service-last-accessed-details --arn arn:aws:iam::123456789012:policy/ExamplePolicy1

use the JobId that was in the output to run the following command. After you do this, you can view the results of the report.

aws iam get-service-last-accessed-details --job-id 98a765b4-3cde-2101-2345-example678f9

For more information, see IAM Access Advisor.

Monitor AWS CloudTrail for suspicious activity

You can monitor AWS CloudTrail for any suspicious activity. Most AWS API calls are logged to AWS CloudTrail as events. They are analyzed by AWS CloudTrail Insights, and you're alerted of any suspicious behavior that's associated with write API calls. This might include a spike in call volume. These alerts include such information as the time the unusual activity occurred and the top identity ARN that contributed to the APIs.

You can identify actions that are performed by tasks with an IAM role in AWS CloudTrail by looking at the event's userIdentity property. In the following example, the arn includes of the name of the assumed role, s3-write-go-bucket-role, followed by the name of the task, 7e9894e088ad416eb5cab92afExample.

"userIdentity": {
    "type": "AssumedRole",
    "principalId": "AROA36C6WWEJ2YEXAMPLE:7e9894e088ad416eb5cab92afExample",
    "arn": "arn:aws:sts::123456789012:assumed-role/s3-write-go-bucket-role/7e9894e088ad416eb5cab92afExample",
    ...
}
Note

When tasks that assume a role are run on Amazon EC2 container instances, a request is logged by Amazon ECS container agent to the audit log of the agent that's located at an address in the /var/log/ecs/audit.log.YYYY-MM-DD-HH format. For more information, see Task IAM Roles Log and Logging Insights Events for Trails.