Setting up Kerberos authentication for PostgreSQL DB clusters

You use AWS Directory Service for Microsoft Active Directory (AWS Managed Microsoft AD) to set up Kerberos authentication for a PostgreSQL DB cluster. To set up Kerberos authentication, take the following steps.

Step 1: Create a directory using AWS Managed Microsoft AD

AWS Directory Service creates a fully managed Active Directory in the AWS Cloud. When you create an AWS Managed Microsoft AD directory, AWS Directory Service creates two domain controllers and DNS servers for you. The directory servers are created in different subnets in a VPC. This redundancy helps make sure that your directory remains accessible even if a failure occurs.

When you create an AWS Managed Microsoft AD directory, AWS Directory Service performs the following tasks on your behalf:

When you launch AWS Directory Service for Microsoft Active Directory, AWS creates an Organizational Unit (OU) that contains all of your directory's objects. This OU, which has the NetBIOS name that you entered when you created your directory, is located in the domain root. The domain root is owned and managed by AWS.

The Admin account that was created with your AWS Managed Microsoft AD directory has permissions for the most common administrative activities for your OU:

The Admin account also has rights to perform the following domain-wide activities:

It takes several minutes for the directory to be created. When it has been successfully created, the Status value changes to Active.

To see information about your directory, choose the directory ID in the directory listing. Make a note of the Directory ID value. You need this value when you create or modify your PostgreSQL DB instance.

Step 2: (Optional) Create a trust relationship between your on-premises Active Directory and AWS Directory Service

If you don't plan to use your own on-premises Microsoft Active Directory, skip to Step 3: Create an IAM role for Amazon Aurora to access the AWS Directory Service.

To get Kerberos authentication using your on-premises Active Directory, you need to create a trusting domain relationship using a forest trust between your on-premises Microsoft Active Directory and the AWS Managed Microsoft AD directory (created in Step 1: Create a directory using AWS Managed Microsoft AD). The trust can be one-way, where the AWS Managed Microsoft AD directory trusts the on-premises Microsoft Active Directory. The trust can also be two-way, where both Active Directories trust each other. For more information about setting up trusts using AWS Directory Service, see When to create a trust relationship in the AWS Directory Service Administration Guide.

Make sure that your on-premises Microsoft Active Directory domain name includes a DNS suffix routing that corresponds to the newly created trust relationship. The following screenshot shows an example.

Step 3: Create an IAM role for Amazon Aurora to access the AWS Directory Service

For Amazon Aurora to call AWS Directory Service for you, your AWS account needs an IAM role that uses the managed IAM policy AmazonRDSDirectoryServiceAccess. This role allows Amazon Aurora to make calls to AWS Directory Service. (Note that this IAM role to access the AWS Directory Service is different than the IAM role used for IAM database authentication.)

When you create a DB instance using the AWS Management Console and your console user account has the iam:CreateRole permission, the console creates the needed IAM role automatically. In this case, the role name is rds-directoryservice-kerberos-access-role. Otherwise, you must create the IAM role manually. When you create this IAM role, choose Directory Service, and attach the AWS managed policy AmazonRDSDirectoryServiceAccess to it.

For more information about creating IAM roles for a service, see Creating a role to delegate permissions to an AWS service in the IAM User Guide.

As an alternative to using the AmazonRDSDirectoryServiceAccess managed policy, you can create policies with the required permissions. In this case, the IAM role must have the following IAM trust policy.

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

The role must also have the following IAM role policy.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": [
        "ds:DescribeDirectories",
        "ds:AuthorizeApplication",
        "ds:UnauthorizeApplication",
        "ds:GetAuthorizedApplicationDetails"
      ],
    "Effect": "Allow",
    "Resource": "*"
    }
  ]
}		

Step 4: Create and configure users

You can create users by using the Active Directory Users and Computers tool. This is one of the Active Directory Domain Services and Active Directory Lightweight Directory Services tools. For more information, see Add Users and Computers to the Active Directory domain in the Microsoft documentation. In this case, users are individuals or other entities, such as their computers that are part of the domain and whose identities are being maintained in the directory.

To create users in an AWS Directory Service directory, you must be connected to a Windows-based Amazon EC2 instance that's a member of the AWS Directory Service directory. At the same time, you must be logged in as a user that has privileges to create users. For more information, see Create a user in the AWS Directory Service Administration Guide.

Step 5: Enable cross-VPC traffic between the directory and the DB instance

If you plan to locate the directory and the DB cluster in the same VPC, skip this step and move on to Step 6: Create or modify a PostgreSQL DB cluster.

If you plan to locate the directory and the DB instance in different VPCs, configure cross-VPC traffic using VPC peering or AWS Transit Gateway.

The following procedure enables traffic between VPCs using VPC peering. Follow the instructions in What is VPC peering? in the Amazon Virtual Private Cloud Peering Guide.

If a different AWS account owns the directory, you must share the directory.

Step 6: Create or modify a PostgreSQL DB cluster

Create or modify a PostgreSQL DB cluster for use with your directory. You can use the console, CLI, or RDS API to associate a DB cluster with a directory. You can do this in one of the following ways:

Kerberos authentication is only supported for PostgreSQL DB clusters in a VPC. The DB cluster can be in the same VPC as the directory, or in a different VPC. The DB cluster must use a security group that allows ingress and egress within the directory's VPC so the DB cluster can communicate with the directory.

Step 7: Create PostgreSQL users for your Kerberos principals

At this point, your Aurora PostgreSQL DB cluster is joined to the AWS Managed Microsoft AD domain. The users that you created in the directory in Step 4: Create and configure users need to be set up as PostgreSQL database users and granted privileges to login to the database. You do that by signing in as the database user with rds_superuser privileges. For example, if you accepted the defaults when you created your Aurora PostgreSQL DB cluster, you use postgres, as shown in the following steps.

After you finish creating all the PostgreSQL users for your Active Directory user identities, users can access the Aurora PostgreSQL DB cluster by using their Kerberos credentials.

It's required that the database users who authenticate using Kerberos are doing so from client machines that are members of the Active Directory domain.

Database users that have been granted the rds_ad role can't also have the rds_iam role. This also applies to nested memberships. For more information, see IAM database authentication.

Configuring your Aurora PostgreSQL DB cluster for case-insensitive user names

Aurora PostgreSQL versions 14.5, 13.8, 12.12, and 11.17 support the krb_caseins_users PostgreSQL parameter. This parameter supports case-insensitive Active Directory user names. By default, this parameter is set to false, so user names are interpreted case-sensitively by Aurora PostgreSQL. That's the default behavior in all older versions of Aurora PostgreSQL. However, you can set this parameter to true in your custom DB cluster parameter group and allow your Aurora PostgreSQL DB cluster to interpret user names, case-insensitively. Consider doing this as a convenience for your database users, who might sometimes mis-type the casing of their user name when authenticating using Active Directory.

To change the krb_caseins_users parameter, your Aurora PostgreSQL DB cluster must be using a custom DB cluster parameter group. For information about working with a custom DB cluster parameter group, see Parameter groups for Amazon Aurora.

You can use the AWS CLI or the AWS Management Console to change the setting. For more information, see Modifying parameters in a DB cluster parameter group in Amazon Aurora.

Step 8: Configure a PostgreSQL client

To configure a PostgreSQL client, take the following steps:

The following is sample krb5.conf content for AWS Managed Microsoft AD.

[libdefaults]
 default_realm = EXAMPLE.COM
[realms]
 EXAMPLE.COM = {
  kdc = example.com
  admin_server = example.com
 }
[domain_realm]
 .example.com = EXAMPLE.COM
 example.com = EXAMPLE.COM

The following is sample krb5.conf content for an on-premises Microsoft Active Directory.

[libdefaults]
 default_realm = EXAMPLE.COM
[realms]
 EXAMPLE.COM = {
  kdc = example.com
  admin_server = example.com
 }
 ONPREM.COM = {
  kdc = onprem.com
  admin_server = onprem.com
 }
[domain_realm]
 .example.com = EXAMPLE.COM
 example.com = EXAMPLE.COM
 .onprem.com = ONPREM.COM
 onprem.com = ONPREM.COM  
 .rds.amazonaws.com = EXAMPLE.COM
 .amazonaws.com.rproxy.goskope.com.cn = EXAMPLE.COM
 .amazon.com = EXAMPLE.COM