Using gMSA for Linux containers on Fargate - Amazon Elastic Container Service

Using gMSA for Linux containers on Fargate

Amazon ECS supports Active Directory authentication for Linux containers on Fargate through a special kind of service account called a group Managed Service Account (gMSA).

Linux based network applications, such as .NET Core applications, can use Active Directory to facilitate authentication and authorization management between users and services. You can use this feature by designing applications that integrate with Active Directory and run on domain-joined servers. But, because Linux containers can't be domain-joined, you need to configure a Linux container to run with gMSA.

Considerations

Consider the following before you use gMSA for Linux containers on Fargate:

  • You must be running Platform Version 1.4 or later.

  • You might need a Windows computer that's joined to the domain to complete the prerequisites. For example, you might need a Windows computer that's joined to the domain to create the gMSA in Active Directory with PowerShell. The RSAT Active Director PowerShell tools are only available for Windows. For more information, see Installing the Active Directory administration tools.

  • You must use domainless gMSA.

    Amazon ECS uses an Active Directory credential specification file (CredSpec). This file contains the gMSA metadata that's used to propagate the gMSA account context to the container. You generate the CredSpec file, and then store it in an Amazon S3 bucket.

  • A task can only support one Active Directory.

Prerequisites

Before you use the gMSA for Linux containers feature with Amazon ECS, make sure to complete the following:

  • You set up an Active Directory domain with the resources that you want your containers to access. Amazon ECS supports the following setups:

    • An AWS Directory Service Active Directory. AWS Directory Service is an AWS managed Active Directory that's hosted on Amazon EC2. For more information, see Getting Started with AWS Managed Microsoft AD in the AWS Directory Service Administration Guide.

    • An on-premises Active Directory. You must ensure that the Amazon ECS Linux container instance can join the domain. For more information, see AWS Direct Connect.

  • You have an existing gMSA account in the Active Directory and a user that has permission to access the gMSA service account. For more information, see Make an Active Directory user for domainless gMSA.

  • You have an Amazon S3 bucket. For more information, see Creating a bucket in the Amazon S3 User Guide.

Setting up gMSA-capable Linux Containers on Amazon ECS

Prepare the infrastructure

The following steps are considerations and setup that are performed once.

  • Make an Active Directory user for domainless gMSA

    When you use domainless gMSA, the container isn't joined to the domain. Other applications that run on the container can't use the credentials to access the domain. Tasks that use a different domain can run on the same container. You provide the name of a secret in AWS Secrets Manager in the CredSpec file. The secret must contain a username, password, and the domain to log in to.

    This feature is similar to the gMSA support for non-domain-joined container hosts feature. For more information about the Windows feature, see gMSA architecture and improvements on the Microsoft Learn website.

    1. Configure a user in your Active Directory domain. The user in the Active Directory must have permission to access the gMSA service account that you use in the tasks.

    2. You have a VPC and subnets that can resolve the Active Directory domain name. Configure the VPC with DHCP options with the domain name that points to the Active Directory service name. For information about how to configure DHCP options for a VPC, see Work with DHCP option sets in the Amazon Virtual Private Cloud User Guide.

    3. Create a secret in AWS Secrets Manager.

    4. Create the credential specification file.

Setting up permissions and secrets

Do the following steps one time for each application and each task definition. We recommend that you use the best practice of granting the least privilege and narrow the permissions used in the policy. This way, each task can only read the secrets that it needs.

  1. Make a user in your Active Directory domain. The user in Active Directory must have permission to access the gMSA service accounts that you use in the tasks.

  2. After you make the Active Directory user, create a secret in AWS Secrets Manager. For more information, see Create an AWS Secrets Manager secret.

  3. Enter the user's username, password, and the domain into JSON key-value pairs called username, password and domainName, respectively.

    {"username":"username","password":"passw0rd", "domainName":"example.com"}
  4. You must add the following permissions as an inline policy to the task execution IAM role. Doing so gives the credentials-fetcher daemon access to the Secrets Manager secret. Replace the MySecret example with the Amazon Resource Name (ARN) of your secret in the Resource list.

    { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "secretsmanager:GetSecretValue" ], "Resource": [ "arn:aws:secretsmanager:aws-region:111122223333:secret:MySecret" ] } ] }
    Note

    If you use your own KMS key to encrypt your secret, you must add the necessary permissions to this role and add this role to the AWS KMS key policy.

  5. Add the credential spec to an Amazon S3 bucket. Then, reference the Amazon Resource Name (ARN) of the Amazon S3 bucket in the credentialSpecs field of the task definition.

    { "family": "", "executionRoleArn": "", "containerDefinitions": [ { "name": "", ... "credentialSpecs": [ "credentialspecdomainless:arn:aws:s3:::${BucketName}/${ObjectName}" ], ... } ], ... }

    To give your tasks access to the S3 bucket, add the following permissions as an inline policy to the Amazon ECS task execution IAM role.

    { "Version": "2012-10-17", "Statement": [ { "Sid": "VisualEditor", "Effect": "Allow", "Action": [ "s3:GetObject", "s3:ListObject" ], "Resource": [ "arn:aws:s3:::{bucket_name}", "arn:aws:s3:::{bucket_name}/{object}" ] } ] }

Credential specification file

Amazon ECS uses an Active Directory credential specification file (CredSpec). This file contains the gMSA metadata that's used to propagate the gMSA account context to the Linux container. You generate the CredSpec and reference it in the credentialSpecs field in your task definition. The CredSpec file doesn't contain any secrets.

The following is an example CredSpec file.

{ "CmsPlugins": [ "ActiveDirectory" ], "DomainJoinConfig": { "Sid": "S-1-5-21-2554468230-2647958158-2204241789", "MachineAccountName": "WebApp01", "Guid": "8665abd4-e947-4dd0-9a51-f8254943c90b", "DnsTreeName": "example.com", "DnsName": "example.com", "NetBiosName": "example" }, "ActiveDirectoryConfig": { "GroupManagedServiceAccounts": [ { "Name": "WebApp01", "Scope": "example.com" } ], "HostAccountConfig": { "PortableCcgVersion": "1", "PluginGUID": "{859E1386-BDB4-49E8-85C7-3070B13920E1}", "PluginInput": { "CredentialArn": "arn:aws:secretsmanager:aws-region:111122223333:secret:MySecret" } } } }
Creating a CredSpec and uploading it to an Amazon S3

You create a CredSpec by using the CredSpec PowerShell module on a Windows computer that's joined to the domain. Follow the steps in Create a credential spec on the Microsoft Learn website.

After you create the credential specification file, upload it to an Amazon S3 bucket. Copy the CredSpec file to the computer or environment that you are running AWS CLI commands in.

Run the following AWS CLI command to upload the CredSpec to Amazon S3. Replace MyBucket with the name of your Amazon S3 bucket. You can store the file as an object in any bucket and location, but you must allow access to that bucket and location in the policy that you attach to the task execution role.

For PowerShell, use the following command:

$ Write-S3Object -BucketName "MyBucket" -Key "ecs-domainless-gmsa-credspec" -File "gmsa-cred-spec.json"

The following AWS CLI command uses backslash continuation characters that are used by sh and compatible shells.

$ aws s3 cp gmsa-cred-spec.json \ s3://MyBucket/ecs-domainless-gmsa-credspec