Karpenter & External residing CMK

[devops-inthe-east]

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A quite simple problem statement has bugged me lately,

Karpenter is unable to provision node groups with AMI that have the EBS volume encrypted with a CMK in an external account.

As the node get created, however instantaneous get terminated due error message : [Client.InvalidKMSKey.InvalidState]

I followed this AWS Document, that'll help me add permissions to the karpenter-worker-nodes roles. however I still get the same error.

The role file looks like this ::

#IAM role and policy for worker node EC2 instances
resource "aws_iam_role" "eks_worker_node_role" {
  name = "${var.cluster_name}-workernode-role"

  assume_role_policy = jsonencode({
    Statement = [{
      Action = "sts:AssumeRole"
      Effect = "Allow"
      Principal = {
        Service = "ec2.amazonaws.com"
      }
    }]
    Version = "2012-10-17"
  })
}

resource "aws_iam_role_policy_attachment" "eks_AmazonEKSWorkerNodePolicy" {
  policy_arn = "arn:aws:iam::aws:policy/AmazonEKSWorkerNodePolicy"
  role       = aws_iam_role.eks_worker_node_role.name
}

resource "aws_iam_role_policy_attachment" "eks_AmazonEKS_CNI_Policy" {
  policy_arn = "arn:aws:iam::aws:policy/AmazonEKS_CNI_Policy"
  role       = aws_iam_role.eks_worker_node_role.name
}

resource "aws_iam_role_policy_attachment" "eks_AmazonEC2ContainerRegistryReadOnly" {
  policy_arn = "arn:aws:iam::aws:policy/AmazonEC2ContainerRegistryReadOnly"
  role       = aws_iam_role.eks_worker_node_role.name
}

resource "aws_iam_role_policy_attachment" "eks_CloudWatchAgentServerPolicy" {
  policy_arn = "arn:aws:iam::aws:policy/CloudWatchAgentServerPolicy"
  role       = aws_iam_role.eks_worker_node_role.name
}

resource "aws_iam_role_policy_attachment" "eks_AmazonEC2RoleforSSM" {
  policy_arn = "arn:aws:iam::aws:policy/service-role/AmazonEC2RoleforSSM"
  role       = aws_iam_role.eks_worker_node_role.name
}

resource "aws_iam_role_policy_attachment" "eks_AmazonS3ReadOnlyAccess" {
  policy_arn = "arn:aws:iam::aws:policy/AmazonS3ReadOnlyAccess"
  role       = aws_iam_role.eks_worker_node_role.name
}

resource "aws_iam_role_policy_attachment" "eks_AmazonSSMManagedInstanceCore" {
  policy_arn = "arn:aws:iam::aws:policy/AmazonSSMManagedInstanceCore"
  role       = aws_iam_role.eks_worker_node_role.name
}

resource "aws_iam_instance_profile" "worker_node_instances_profile" {
  name = "${var.cluster_name}-instance-profile"
  role = aws_iam_role.eks_worker_node_role.name
}


data "aws_eks_cluster" "cluster" {
  name = var.cluster_name
}

locals {
  worker_node_role_arn = aws_iam_role.eks_worker_node_role.arn
}

data "aws_iam_policy_document" "karpenter_controller_assume_role_policy" {
  statement {
    actions = ["sts:AssumeRoleWithWebIdentity"]
    effect  = "Allow"
    condition {
      test     = "StringEquals"
      variable = "${replace(data.aws_eks_cluster.cluster.identity[0].oidc[0].issuer, "https://", "")}:sub"
      values   = ["system:serviceaccount:karpenter:karpenter"]
    }  
    condition {
      test     = "StringEquals"
      variable = "${replace(data.aws_eks_cluster.cluster.identity[0].oidc[0].issuer, "https://", "")}:aud"
      values   = ["sts.amazonaws.com"]
    }
    principals {
      identifiers = ["arn:aws:iam::${var.tenantaccount}:oidc-provider/${replace(data.aws_eks_cluster.cluster.identity[0].oidc[0].issuer, "https://", "")}"]
      type        = "Federated"
    }
  }
}

resource "aws_iam_role" "karpenter_controller" {
  assume_role_policy = data.aws_iam_policy_document.karpenter_controller_assume_role_policy.json
  name               = "${var.cluster_name}-KarpenterRole"
}

resource "aws_iam_policy" "karpenter_controller" {
  name        = "${var.cluster_name}-KarpenterPolicy"
  description = "Karpenter controller policy for autoscaling"
  policy = <<EOF
{
    "Statement": [
        {
            "Action": [
                "ssm:GetParameter",
                "ec2:DescribeImages",
                "ec2:RunInstances",
                "ec2:DescribeSubnets",
                "ec2:DescribeSecurityGroups",
                "ec2:DescribeLaunchTemplates",
                "ec2:DescribeInstances",
                "ec2:DescribeInstanceTypes",
                "ec2:DescribeInstanceTypeOfferings",
                "ec2:DescribeAvailabilityZones",
                "ec2:DeleteLaunchTemplate",
                "ec2:CreateTags",
                "ec2:CreateLaunchTemplate",
                "ec2:CreateFleet",
                "ec2:DescribeSpotPriceHistory",
                "pricing:GetProducts",
                "kms:Encrypt",
                "kms:Decrypt",
                "kms:ReEncrypt*",
                "kms:GenerateDataKey*",
                "kms:DescribeKey"
                
            ],
            "Effect": "Allow",
            "Resource": "*",
            "Sid": "Karpenter"
        },
        {
            "Action": "ec2:TerminateInstances",
            "Condition": {
                "StringLike": {
                    "ec2:ResourceTag/karpenter.sh/nodepool": "*"
                }
            },
            "Effect": "Allow",
            "Resource": "*",
            "Sid": "ConditionalEC2Termination"
        },
        {
            "Effect": "Allow",
            "Action": "iam:PassRole",
            "Resource": "${local.worker_node_role_arn}",
            "Sid": "PassNodeIAMRole"
        },
        {
            "Effect": "Allow",
            "Action": "eks:DescribeCluster",
            "Resource": "arn:aws:eks:${var.region}:${var.tenantaccount}:cluster/${var.cluster_name}",
            "Sid": "EKSClusterEndpointLookup"
        },
        {
            "Sid": "AllowScopedInstanceProfileCreationActions",
            "Effect": "Allow",
            "Resource": "*",
            "Action": [
            "iam:CreateInstanceProfile"
            ],
            "Condition": {
            "StringEquals": {
                "aws:RequestTag/kubernetes.io/cluster/${var.cluster_name}": "owned",
                "aws:RequestTag/topology.kubernetes.io/region": "${var.region}"
            },
            "StringLike": {
                "aws:RequestTag/karpenter.k8s.aws/ec2nodeclass": "*"
            }
            }
        },
        {
            "Sid": "AllowScopedInstanceProfileTagActions",
            "Effect": "Allow",
            "Resource": "*",
            "Action": [
            "iam:TagInstanceProfile"
            ],
            "Condition": {
            "StringEquals": {
                "aws:ResourceTag/kubernetes.io/cluster/${var.cluster_name}": "owned",
                "aws:ResourceTag/topology.kubernetes.io/region": "${var.region}",
                "aws:RequestTag/kubernetes.io/cluster/${var.cluster_name}": "owned",
                "aws:RequestTag/topology.kubernetes.io/region": "${var.region}"
            },
            "StringLike": {
                "aws:ResourceTag/karpenter.k8s.aws/ec2nodeclass": "*",
                "aws:RequestTag/karpenter.k8s.aws/ec2nodeclass": "*"
            }
            }
        },
        {
            "Sid": "AllowScopedInstanceProfileActions",
            "Effect": "Allow",
            "Resource": "*",
            "Action": [
            "iam:AddRoleToInstanceProfile",
            "iam:RemoveRoleFromInstanceProfile",
            "iam:DeleteInstanceProfile",
            "iam:CreateServiceLinkedRole",
            "iam:ListRoles",
            "iam:ListInstanceProfiles"
            ],
            "Condition": {
            "StringEquals": {
                "aws:ResourceTag/kubernetes.io/cluster/${var.cluster_name}": "owned",
                "aws:ResourceTag/topology.kubernetes.io/region": "${var.region}"
            },
            "StringLike": {
                "aws:ResourceTag/karpenter.k8s.aws/ec2nodeclass": "*"
            }
            }
        },
        {
            "Sid": "AllowInstanceProfileReadActions",
            "Effect": "Allow",
            "Resource": "*",
            "Action": "iam:GetInstanceProfile"
        }
    ],
    "Version": "2012-10-17"
  }
  EOF
}

resource "aws_iam_role_policy_attachment" "karpenter_controller_attach" {
depends_on = [aws_iam_policy.karpenter_controller, aws_iam_role.karpenter_controller]
role = aws_iam_role.karpenter_controller.name
policy_arn = aws_iam_policy.karpenter_controller.arn
}

`

---

Few Qs,

I currently use following seq to provision my nodegroup

1. EKS Control provisioned by Terraform.
2. Karpenter Pods with Fargate Profile will provision the nodegroup referencing the AMI.
3. NodeGroup is provisioned with CoreDNS the first pod to get placed.

A grant is been created on the Key owner account & cross-account-kms on the consumer account

I was curious to know, if there are any other piece of infra need to integrated so that Karpenter can create nodegroups from AMIs that have encrypted snapshot with an external residing CMK.

[devops-inthe-east]

There is one thing that I missed out on, I was able it work by creating a 'new' Grant in the account that is consuming the KMS for the autoscaling role.

Support engineers indicate that this should be a one time activity for when a new autoscaling role get created.

[devops-inthe-east]

The updated iam.tf will have the following lines of permission to add the CreateGrant action.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "AllowCreationOfGrantForTheKMSKeyinExternalAccount444455556666",
      "Effect": "Allow",
      "Action": "kms:CreateGrant",
      "Resource": "arn:aws:kms:us-west-2:444455556666:key/1a2b3c4d-5e6f-1a2b-3c4d-5e6f1a2b3c4d"
    }
  ]
}

The awscli cmd :

aws kms create-grant \
  --region us-west-2 \
  --key-id arn:aws:kms:us-west-2:444455556666:key/1a2b3c4d-5e6f-1a2b-3c4d-5e6f1a2b3c4d \
  --grantee-principal arn:aws:iam::111122223333:role/aws-service-role/autoscaling.amazonaws.com/AWSServiceRoleForAutoScaling \
  --operations "Encrypt" "Decrypt" "ReEncryptFrom" "ReEncryptTo" "GenerateDataKey" "GenerateDataKeyWithoutPlaintext" "DescribeKey" "CreateGrant" 

However what bugs me is the fact that the CT logs indicate the my full admin role as 'username' making the 'CreateGrant' API call.

When it should be the autoscaling group role making the trigger.

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