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Creating a ROSA cluster in STS mode with custom KMS key

Byron Miller

Last updated 4/21/2022

Tip Official Documentation ROSA STS with custom KMS key

This guide will walk you through installing ROSA (Red Hat OpenShift Service on AWS) with a customer-provided KMS key that will be used to encrypt both the root volumes of nodes as well as persistent volumes for mounted EBS claims.

Prerequisites

AWS CLI
ROSA CLI v1.1.11 or higher
OpenShift CLI - rosa download openshift-client

Prepare AWS Account for ROSA

Configure the AWS CLI by running the following command
```
aws configure
```
You will be required to enter an AWS Access Key ID and an AWS Secret Access Key along with a default region name and output format
```
% aws configure
AWS Access Key ID []: 
AWS Secret Access Key []: 
Default region name [us-east-2]: 
Default output format [json]:
```
The AWS Access Key ID and AWS Secret Access Key values can be obtained by logging in to the AWS console and creating an Access Key in the Security Credentials section of the IAM dashboard for your user
Validate your credentials
```
aws sts get-caller-identity
```
You should receive output similar to the following
```
{
  "UserId": <your ID>,
  "Account": <your account>,
  "Arn": <your arn>
}
```
You will need to save the account ID for adding it to your KMS key to define installer role, so take note.
If this is a brand new AWS account that has never had a AWS Load Balancer installed in it, you should run the following
```
aws iam create-service-linked-role --aws-service-name \
"elasticloadbalancing.amazonaws.com"
```
Set the AWS region you plan to deploy your cluser into. For this example, we will deploy into us-east-2.
```
export AWS_REGION="us-east-2"
```

Create KMS Key

For this example, we will create a custom KMS key using the AWS CLI. If you would prefer, you could use an existing key instead.

Create a customer-managed KMS key

KMS_ARN=$(aws kms create-key --region $AWS_REGION --description 'Custom ROSA Encryption Key' --query KeyMetadata.Arn --output text) 

This command will save the ARN output of this custom key for further steps.

Generate the necessary key policy to allow the ROSA STS roles to access the key. Use the below command to populate a sample policy, or create your own.

Important note, if you specify a custom STS role prefix, you will need to update that in the command below.

AWS_ACCOUNT=$(aws sts get-caller-identity --query Account --output text); cat << EOF > rosa-key-policy.json
{
    "Version": "2012-10-17",
    "Id": "key-rosa-policy-1",
    "Statement": [
        {
            "Sid": "Enable IAM User Permissions",
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::${AWS_ACCOUNT}:root"
            },
            "Action": "kms:*",
            "Resource": "*"
        },
        {
            "Sid": "Allow ROSA use of the key",
            "Effect": "Allow",
            "Principal": {
                "AWS": [
                    "arn:aws:iam::${AWS_ACCOUNT}:role/ManagedOpenShift-Support-Role",
                    "arn:aws:iam::${AWS_ACCOUNT}:role/ManagedOpenShift-Installer-Role",
                    "arn:aws:iam::${AWS_ACCOUNT}:role/ManagedOpenShift-Worker-Role",
                    "arn:aws:iam::${AWS_ACCOUNT}:role/ManagedOpenShift-ControlPlane-Role"
                ]
            },
            "Action": [
                "kms:Encrypt",
                "kms:Decrypt",
                "kms:ReEncrypt*",
                "kms:GenerateDataKey*",
                "kms:DescribeKey"
            ],
            "Resource": "*"
        },
        {
            "Sid": "Allow attachment of persistent resources",
            "Effect": "Allow",
            "Principal": {
                "AWS": [
                    "arn:aws:iam::${AWS_ACCOUNT}:role/ManagedOpenShift-Support-Role",
                    "arn:aws:iam::${AWS_ACCOUNT}:role/ManagedOpenShift-Installer-Role",
                    "arn:aws:iam::${AWS_ACCOUNT}:role/ManagedOpenShift-Worker-Role",
                    "arn:aws:iam::${AWS_ACCOUNT}:role/ManagedOpenShift-ControlPlane-Role"
                ]
            },
            "Action": [
                "kms:CreateGrant",
                "kms:ListGrants",
                "kms:RevokeGrant"
            ],
            "Resource": "*",
            "Condition": {
                "Bool": {
                    "kms:GrantIsForAWSResource": "true"
                }
            }
        }
    ]
}
EOF

Apply the newly generated key policy to the custom KMS key.

aws kms put-key-policy --key-id $KMS_ARN \
--policy file://rosa-key-policy.json \
--policy-name default

Create ROSA Cluster

Make sure your ROSA CLI version is at minimum v1.1.11 or higher.
```
rosa version
```
Create the ROSA STS Account Roles

If you have already installed account-roles into your aws account, you can skip this step.
```
rosa create account-roles --mode auto -y
```
Set Environment Variables
```
ROSA_CLUSTER_NAME=poc-kmskey
```

Using the ROSA CLI, create your cluster.

While this is an example, feel free to customize this command to best suit your needs.

rosa create cluster --cluster-name $ROSA_CLUSTER_NAME --sts \
--region $AWS_REGION --compute-nodes 2 --machine-cidr 10.0.0.0/16 \
--service-cidr 172.30.0.0/16 --pod-cidr 10.128.0.0/14 --host-prefix 23 \
--kms-key-arn $KMS_ARN

Create the operator roles necessary for the cluster to function.

rosa create operator-roles -c $ROSA_CLUSTER_NAME --mode auto --yes

Create the OIDC provider necessary for the cluster to authenticate.

rosa create oidc-provider -c $ROSA_CLUSTER_NAME --mode auto --yes

Validate that the cluster is now installing. Within 5 minutes, the cluster state should move beyond pending and show installing.
```
watch "rosa describe cluster -c $ROSA_CLUSTER_NAME"
```

Watch the install logs as the cluster installs.

rosa logs install -c $ROSA_CLUSTER_NAME --watch --tail 10

Validate the cluster

Once the cluster has finished installing we can validate our access to the cluster.

Create an Admin user
```
rosa create admin -c $ROSA_CLUSTER_NAME
```
Run the resulting login statement from output. May take 2-3 minutes before authentication is fully synced

Verify the default persistent volumes in the cluster.

oc get pv

Output:

NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM
                                    STORAGECLASS       REASON   AGE
pvc-00dac374-a45e-43fa-a313-ae0491e8edf1   10Gi       RWO            Delete           Bound    openshift-monitoring/alertmanager-data-alertmanager-main-1   gp2-customer-kms            26m
pvc-7d211496-4ddf-4200-921c-1404b754afa5   10Gi       RWO            Delete           Bound    openshift-monitoring/alertmanager-data-alertmanager-main-0   gp2-customer-kms            26m
pvc-b5243cef-ec30-4e5c-a348-aeb8136a908c   100Gi      RWO            Delete           Bound    openshift-monitoring/prometheus-data-prometheus-k8s-0        gp2-customer-kms            26m
pvc-ec60c1cf-72cf-4ac6-ab12-8e9e5afdc15f   100Gi      RWO            Delete           Bound    openshift-monitoring/prometheus-data-prometheus-k8s-1        gp2-customer-kms            26m

You should see the StroageClass set to gp2-customer-kms. This is the default StorageClass which is encrypted using the customer-provided key.

Cleanup

Delete the ROSA cluster

rosa delete cluster -c $ROSA_CLUSTER_NAME

Once the cluster is deleted, delete the cluster’s STS roles.

rosa delete operator-roles -c $ROSA_CLUSTER_NAME --yes --mode auto
rosa delete oidc-provider -c $ROSA_CLUSTER_NAME  --yes --mode auto