amazon-s3kubernetesterraformopenid-connectk8s-serviceaccount

How do you obtain an aws-iam-token to access S3 using IRSA?

I've create an IRSA role in terraform so that the associated service account can be used by a K8s job to access an S3 bucket but I keep getting an AccessDenied error within the job.

I first enabled IRSA in our EKS cluster with enable_irsa = true in our eks module.

I then created a simple aws_iam_policy as:

resource "aws_iam_policy" "eks_s3_access_policy" {
  name = "eks_s3_access_policy"

  policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Action = [
          "s3:*",
        ]
        Effect   = "Allow"
        Resource = "arn:aws:s3:::*"
      },
    ]
  })
}

and a iam-assumable-role-with-oidc:

module "iam_assumable_role_with_oidc_for_s3_access" {
  source  = "terraform-aws-modules/iam/aws//modules/iam-assumable-role-with-oidc"
  version = "~> 3.0"

  create_role = true
  role_name = "eks-s3-access"
  role_description = "Role to access s3 bucket"
  tags = { Role = "eks_s3_access_policy" }
  provider_url = replace(module.eks.cluster_oidc_issuer_url, "https://", "")
  role_policy_arns = [aws_iam_policy.eks_s3_access_policy.arn]
  number_of_role_policy_arns = 1
  oidc_fully_qualified_subjects = ["system:serviceaccount:default:my-user"]
}

I created a K8s service account using Helm like:

Name:                my-user
Namespace:           default
Labels:              app.kubernetes.io/managed-by=Helm
Annotations:         eks.amazonaws.com/role-arn: arn:aws:iam::111111:role/eks-s3-access
                     meta.helm.sh/release-name: XXXX
                     meta.helm.sh/release-namespace: default
Image pull secrets:  <none>
Mountable secrets:   my-user-token-kwwpq
Tokens:              my-user-token-kwwpq
Events:              <none>

Finally, jobs are created using the K8s API from a job template:

apiVersion: batch/v1
kind: Job
metadata:
  name: job
  namespace: default
spec:
  template:
  spec:
    serviceAccountName: my-user
    containers:
    - name: {{ .Chart.Name }}
      env:
      - name: AWS_ROLE_ARN
        value: arn:aws:iam::746181457053:role/eks-s3-access
      - name: AWS_WEB_IDENTITY_TOKEN_FILE
        value: /var/run/secrets/eks.amazonaws.com/serviceaccount/token
      volumeMounts:
      - mountPath: /var/run/secrets/eks.amazonaws.com/serviceaccount
        name: aws-iam-token
        readOnly: true
    volumes:
    - name: aws-iam-token
      projected:
        defaultMode: 420
        sources:
        - serviceAccountToken:
          audience: sts.amazonaws.com
          expirationSeconds: 86400
          path: token

When the job attempts to get the specified credentials, however, the specified token is not there:

2021-08-03 18:02:41  Refreshing temporary credentials failed during mandatory refresh period.
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/aiobotocore/credentials.py", line 291, in _protected_refresh
    metadata = await self._refresh_using()
  File "/usr/local/lib/python3.7/site-packages/aiobotocore/credentials.py", line 345, in fetch_credentials
    return await self._get_cached_credentials()
  File "/usr/local/lib/python3.7/site-packages/aiobotocore/credentials.py", line 355, in _get_cached_credentials
    response = await self._get_credentials()
  File "/usr/local/lib/python3.7/site-packages/aiobotocore/credentials.py", line 410, in _get_credentials
    kwargs = self._assume_role_kwargs()
  File "/usr/local/lib/python3.7/site-packages/aiobotocore/credentials.py", line 420, in _assume_role_kwargs
    identity_token = self._web_identity_token_loader()
  File "/usr/local/lib/python3.7/site-packages/botocore/utils.py", line 2365, in __call__
    with self._open(self._web_identity_token_path) as token_file:
FileNotFoundError: [Errno 2] No such file or directory: '/var/run/secrets/eks.amazonaws.com/serviceaccount/token'

From what is described in https://aws.amazon.com/blogs/opensource/introducing-fine-grained-iam-roles-service-accounts/ a webhook typically creates these credentials when the pod is created. However, since we're creating the new k8s' job on demand within the k8s cluster, I suspect that the webhook is not creating any such credentials.

How can I request the correct credentials to be created from within a K8s cluster? Is there a way to instantiate the webhook from within the cluster?

Solution

  • There are a couple of things that could cause this to fail.