Using IAM to control file system data access

You can use both IAM identity policies and resource policies to control client access to Amazon EFS resources in a way that is scalable and optimized for cloud environments. Using IAM, you can permit clients to perform specific actions on a file system, including read-only, write, and root access. An "allow" permission on an action in either an IAM identity policy or a file system resource policy allows access for that action. The permission does not need to be granted in both an identity and a resource policy.

NFS clients can identify themselves using an IAM role when connecting to an EFS file system. When a client connects to a file system, Amazon EFS evaluates the file system’s IAM resource policy, which is called a file system policy, along with any identity-based IAM policies to determine the appropriate file system access permissions to grant.

When you use IAM authorization for NFS clients, client connections and IAM authorization decisions are logged to AWS CloudTrail. For more information about how to log Amazon EFS API calls with CloudTrail, see Logging Amazon EFS API Calls with AWS CloudTrail.

Important

You must use the EFS mount helper to mount your Amazon EFS file systems in order to use IAM authorization to control client access. For more information, see Mounting with IAM authorization.

Default EFS file system policy

The default EFS file system policy does not use IAM to authenticate, and grants full access to any anonymous client that can connect to the file system using a mount target. The default policy is in effect whenever a user-configured file system policy is not in effect, including at file system creation. Whenever the default file system policy is in effect, a DescribeFileSystemPolicy API operation returns a PolicyNotFound response.

EFS actions for clients

You can specify the following actions for clients accessing a file system using a file system policy.

Action	Description
elasticfilesystem:ClientMount	Provides read-only access to a file system.
elasticfilesystem:ClientWrite	Provides write permissions on a file system.
elasticfilesystem:ClientRootAccess	Provides use of the root user when accessing a file system.

EFS condition keys for clients

To express conditions, you use predefined condition keys. Amazon EFS has the following predefined condition keys for NFS clients.

EFS Condition Key	Description	Operator
aws:SecureTransport	Use this key to require clients to use TLS when connecting to an EFS file system.	Boolean
elasticfilesystem:AccessPointArn	ARN of the EFS access point to which the client is connecting.	String
elasticfilesystem:AccessedViaMountTarget	Use this key to prevent access to an EFS file system by clients that are not using file system mount targets.	Boolean

File system policy examples

In this section, you can find example file system policies that grant or deny permissions for various Amazon EFS actions. Amazon EFS file system policies have a 20,000 character limit. For information about the elements of a resource-based policy, see Specifying policy elements: actions, effects, and principals.

Important

If you grant permission to an individual IAM user or role in a file system policy, don't delete or recreate that user or role while the policy is in effect on the file system. If this happens, that user or role is effectively locked out from file system and will not be able to access it. For more information, see Specifying a Principal in the IAM User Guide.

For information about how to create a file system policy, see Creating file system policies.

Example 1: Grant read and write access to a specific AWS role

This example EFS file system policy has the following characteristics:

• The effect is Allow.

• The principal is set to the Testing_Role in the AWS account.

• The action is set to ClientMount (read), and ClientWrite.

• The condition for granting permissions is set to AccessedViaMountTarget.

{
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::111122223333:role/Testing_Role"
            },
            "Action": [
                "elasticfilesystem:ClientWrite",
                "elasticfilesystem:ClientMount"
            ],
            "Resource": "arn:aws:elasticfilesystem:us-east-2:111122223333:file-system/fs-1234abcd",
            "Condition": {
                "Bool": {
                    "elasticfilesystem:AccessedViaMountTarget": "true"
                }
            }
        }
    ]
}

Example 2: Grant read-only access

The following file system policy only grants ClientMount, or read-only, permissions to the EfsReadOnly IAM role.

{
    "Id": "read-only-example-policy02",
    "Statement": [
        {
            "Sid": "efs-statement-example02",
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::111122223333:role/EfsReadOnly"
            },
            "Action": [
                "elasticfilesystem:ClientMount"
            ],
            "Resource": "arn:aws:elasticfilesystem:us-east-2:111122223333:file-system/fs-12345678"            
        }
    ]
}

To learn how to set additional file system policies, including denying root access to all IAM principals, except for a specific management workstation, see Walkthrough: Enable root squashing using IAM authorization for NFS clients.

Example 3: Grant access to an EFS Access Point

You use an EFS access policy to provide an NFS client with an application-specific view into shared file-based datasets on an EFS file system. You grant the access point permissions on the file system using a file system policy. This file policy example uses a condition element to grant a specific access point that is identified by its ARN full access to the file system. For more information about using EFS access points, see Working with Amazon EFS access points.

{
    "Id": "access-point-example03",
    "Statement": [
        {
            "Sid": "access-point-statement-example03",
            "Effect": "Allow",
            "Principal": {"AWS": "arn:aws:iam::555555555555:role/EfsAccessPointFullAccess"},
            "Action": "elasticfilesystem:Client*",
            "Resource": "arn:aws:elasticfilesystem:us-east-2:111122223333:file-system/fs-12345678",
            "Condition": { 
                "StringEquals": {
                    "elasticfilesystem:AccessPointArn":"arn:aws:elasticfilesystem:us-east-2:555555555555:access-point/fsap-12345678" } 
            }            
        }
    ]
}