Grant a user permissions to pass a role to an AWS service

To configure many AWS services, you must pass an IAM role to the service. This allows the service to assume the role later and perform actions on your behalf. For most services, you only have to pass the role to the service once during setup, and not every time that the service assumes the role. For example, assume that you have an application running on an Amazon EC2 instance. That application requires temporary credentials for authentication, and permissions to authorize the application to perform actions in AWS. When you set up the application, you must pass a role to Amazon EC2 to use with the instance that provides those credentials. You define the permissions for the applications running on the instance by attaching an IAM policy to the role. The application assumes the role every time it needs to perform the actions that are allowed by the role.

To pass a role (and its permissions) to an AWS service, a user must have permissions to pass the role to the service. This helps administrators ensure that only approved users can configure a service with a role that grants permissions. To allow a user to pass a role to an AWS service, you must grant the PassRole permission to the user's IAM user, role, or group.

When setting the PassRole permission, you should make sure that a user doesn’t pass a role where the role has more permissions than you want the user to have. For example, Alice might not be allowed to perform any Amazon S3 actions. If Alice could pass a role to a service that allows Amazon S3 actions, the service could perform Amazon S3 actions on behalf of Alice when executing the job.

When you specify a service-linked role, you must also have permission to pass that role to the service. Some services automatically create a service-linked role in your account when you perform an action in that service. For example, Amazon EC2 Auto Scaling creates the AWSServiceRoleForAutoScaling service-linked role for you when you create an Auto Scaling group for the first time. If you try to specify the service-linked role when you create an Auto Scaling group and you don't have the iam:PassRole permission, you receive an error. If you don't explicitly specify the role, the iam:PassRole permission is not required, and the default is to use AWSServiceRoleForAutoScaling role for all operations that are performed on that group. To learn which services support service-linked roles, see AWS services that work with IAM. To learn which services automatically create a service-linked role when you perform an action in that service, choose the Yes link and view the service-linked role documentation for the service.

A user can pass a role ARN as a parameter in any API operation that uses the role to assign permissions to the service. The service then checks whether that user has the iam:PassRole permission. To limit the user to passing only approved roles, you can filter the iam:PassRole permission with the Resources element of the IAM policy statement.

You can use the Condition element in a JSON policy to test the value of keys included in the request context of all AWS requests. To learn more about using condition keys in a policy, see IAM JSON policy elements: Condition. The iam:PassedToService condition key can be used to specify the service principal of the service to which a role can be passed. To learn more about using the iam:PassedToService condition key in a policy, see iam:PassedToService.

Example 1

Suppose you want to grant a user the ability to pass any of an approved set of roles to the Amazon EC2 service upon launching an instance. You need three elements:

Now the user can start an Amazon EC2 instance with an assigned role. Applications running on the instance can access temporary credentials for the role through the instance profile metadata. The permissions policies attached to the role determine what the instance can do.

Example 2

Amazon Relational Database Service (Amazon RDS) supports a feature called Enhanced Monitoring. This feature enables Amazon RDS to monitor a database instance using an agent. It also allows Amazon RDS to log metrics to Amazon CloudWatch Logs. To enable this feature, you must create a service role to give Amazon RDS permissions to monitor and write metrics to your logs.

The role automatically gets a trust policy that grants the monitoring.rds.amazonaws.com service permissions to assume the role. After it does, Amazon RDS can perform all of the actions that the AmazonRDSEnhancedMonitoringRole policy allows.

The user that you want to access Enhanced Monitoring needs a policy that includes a statement that allows the user to to list the RDS roles and a statement that allows the user to pass the role, like the following. Use your account number and replace the role name with the name you provided in step 6.

    {
      "Sid": "PolicyStatementToAllowUserToListRoles",
      "Effect": "Allow",
      "Action": ["iam:ListRoles"],
      "Resource": "*"
    },
    {
        "Sid": "PolicyStatementToAllowUserToPassOneSpecificRole",
        "Effect": "Allow",
        "Action": [ "iam:PassRole" ],
        "Resource": "arn:aws:iam::account-id:role/RDS-Monitoring-Role"
    }
   

You can combine this statement with statements in another policy or put it in its own policy. To instead specify that the user can pass any role that begins with RDS-, you can replace the role name in the resource ARN with a wildcard, as follows.

        "Resource": "arn:aws:iam::account-id:role/RDS-*"

iam:PassRole actions in AWS CloudTrail logs

PassRole is not an API call. PassRole is a permission, meaning no CloudTrail logs are generated for IAM PassRole. To review what roles are passed to which AWS services in CloudTrail, you must review the CloudTrail log that created or modified the AWS resource receiving the role. For example, a role is passed to an AWS Lambda function when it's created. The log for the CreateFunction action shows a record of role that was passed to the function.