Chapter 3. AWS STS and ROSA with HCP explained

As part of ROSA with HCP, Red Hat must be granted the necessary permissions to manage infrastructure resources in your AWS account. ROSA with HCP grants the cluster’s automation software limited, short-term access to resources in your AWS account.

The STS method uses predefined roles and policies to grant temporary, least-privilege permissions to IAM roles. The credentials typically expire an hour after being requested. Once expired, they are no longer recognized by AWS and no longer have account access from API requests made with them. For more information, see the AWS documentation.

AWS IAM STS roles must be created for each ROSA with HCP cluster. The ROSA command line interface (CLI) (rosa) manages the STS roles and helps you attach the ROSA-specific, AWS-managed policies to each role. The CLI provides the commands and files to create the roles, attach the AWS-managed policies, and an option to allow the CLI to automatically create the roles and attach the policies.

Security features for AWS STS include:

ROSA with HCP grants cluster software components least-privilege permissions with short-term security credentials to specific and segregated IAM roles. The credentials are associated with IAM roles specific to each component and cluster that makes AWS API calls. This method aligns with principles of least-privilege and secure practices in cloud service resource management.

Deploying a ROSA with HCP cluster follows the following steps:

During the cluster creation process, the ROSA CLI creates the required JSON files for you and outputs the commands you need. If desired, the ROSA CLI can also run the commands for you.

The ROSA CLI can automatically create the roles for you, or you can manually create them by using the --mode manual or --mode auto flags. For further details about deployment, see Creating a cluster with customizations.

The user creates the required account-wide roles. During role creation, a trust policy, known as a cross-account trust policy, is created which allows a Red Hat-owned role to assume the roles. Trust policies are also created for the EC2 service, which allows workloads on EC2 instances to assume roles and obtain credentials. AWS assigns a corresponding permissions policy to each role.

After the account-wide roles and policies are created, the user can create a cluster. Once cluster creation is initiated, the user creates the Operator roles so that cluster Operators can make AWS API calls. These roles are then assigned to the corresponding permission policies that were created earlier and a trust policy with an OIDC provider. The Operator roles differ from the account-wide roles in that they ultimately represent the pods that need access to AWS resources. Because a user cannot attach IAM roles to pods, they must create a trust policy with an OIDC provider so that the Operator, and therefore the pods, can access the roles they need.

Once the user assigns the roles to the corresponding policy permissions, the final step is creating the OIDC provider.

When a new role is needed, the workload currently using the Red Hat role will assume the role in the AWS account, obtain temporary credentials from AWS STS, and begin performing the actions using API calls within the user’s AWS account as permitted by the assumed role’s permissions policy. The credentials are temporary and have a maximum duration of one hour.

Operators use the following process to obtain the requisite credentials to perform their tasks. Each Operator is assigned an Operator role, a permissions policy, and a trust policy with an OIDC provider. The Operator will assume the role by passing a JSON web token that contains the role and a token file (web_identity_token_file) to the OIDC provider, which then authenticates the signed key with a public key. The public key is created during cluster creation and stored in an S3 bucket. The Operator then confirms that the subject in the signed token file matches the role in the role trust policy which ensures that the OIDC provider can only obtain the allowed role. The OIDC provider then returns the temporary credentials to the Operator so that the Operator can make AWS API calls. For a visual representation, see the following diagram: