Securing Kubernetes

The following guide covers how to secure Kubernetes using Pomerium. This is achieved by:

• creating a ClusterRoleBinding for a user,
• setting a route through Pomerium to the Kubernetes API server,
• configuring a kubectl context to connect and authorize to the API server through Pomerium.

Before You Begin

• This guide assumes you've already installed Pomerium in a Kubernetes cluster using our Helm charts. Follow Pomerium using Helm before proceeding.
• This guide assumes you have a certificate solution in place, such as Cert-Manager.

Pomerium Service Account

Pomerium uses a single service account and user impersonation headers to authenticate and authorize users in Kubernetes. This service account is automatically created by our Helm chart. If you've installed Pomerium without our charts, expand below to manually create the service account.

Manually create service account

To create the Pomerium service account use the following configuration file:

pomerium-k8s.yaml

---
apiVersion: v1
kind: ServiceAccount
metadata:
  namespace: default
  name: pomerium
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: pomerium-impersonation
rules:
  - apiGroups:
      - ""
    resources:
      - users
      - groups
      - serviceaccounts
    verbs:
      - impersonate
  - apiGroups:
      - "authorization.k8s.io"
    resources:
      - selfsubjectaccessreviews
    verbs:
      - create
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: pomerium
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: pomerium-impersonation
subjects:
  - kind: ServiceAccount
    name: pomerium
    namespace: default

Apply the configuration with:

kubectl apply -f ./pomerium-k8s.yaml

User Permissions

1. To grant access to users within Kubernetes, you will need to configure role-based access control (RBAC) permissions. For example, consider the example below:

   rbac-someuser.yaml

   apiVersion: rbac.authorization.k8s.io/v1
   kind: ClusterRoleBinding
   metadata:
     name: cluster-admin-crb
   roleRef:
     apiGroup: rbac.authorization.k8s.io
     kind: ClusterRole
     name: cluster-admin
   subjects:
     - apiGroup: rbac.authorization.k8s.io
       kind: User
       name: someuser@example.com

2. Apply the RBAC ClusterRoleBinding:

   kubectl apply -f rbac-someuser.yaml

Permissions can also be granted to groups the Pomerium user is a member of. This allows you to set a single ClusterRoleBinding in Kubernetes and modify access from your IdP.

Create a Route for the API server

This new route requires a kubernetes service account token. Our Helm chart creates one and makes it available at /var/run/secrets/kubernetes.io/serviceaccount/token.

1. Update your pomerium-values.yaml file with the following route:

   pomerium-values.yaml

     routes:
       - from: https://k8s.localhost.pomerium.io
         to: https://kubernetes.default.svc.cluster.local
         allow_spdy: true
         tls_skip_verify: true
         kubernetes_service_account_token_file: /var/run/secrets/kubernetes.io/serviceaccount/token
         policy:
           - allow:
               or:
                 - domain:
                     is: pomerium.com

   Change the policy to match your configuration.

2. Apply the updated values with Helm:

   helm upgrade --install pomerium pomerium/pomerium --values pomerium-values.yaml

   This will create a Pomerium route within kubernetes that is accessible from *.localhost.pomerium.io.

Configure Kubectl

The pomerium-cli tool can be used by kubectl as a credential plugin. Once configured, connections to the cluster will open a browser window to the Pomerium authenticate service and generate an authentication token that will be used for Kubernetes API calls.

To use pomerium-cli as an exec-credential provider, update your kubectl config:

# Add Cluster
kubectl config set-cluster via-pomerium --server=https://k8s.localhost.pomerium.io
# Add Context
kubectl config set-context via-pomerium --user=via-pomerium --cluster=via-pomerium
# Add credentials command
kubectl config set-credentials via-pomerium --exec-command=pomerium-cli \
  --exec-arg=k8s,exec-credential,https://k8s.localhost.pomerium.io \
  --exec-api-version=client.authentication.k8s.io/v1beta1

Skip TLS Verification

If you're using untrusted certificates or need to debug a certificate issue, configure the credential provider without TLS verification:

kubectl config set-cluster via-pomerium --server=https://k8s.localhost.pomerium.io \
  --insecure-skip-tls-verify=true
kubectl config set-credentials via-pomerium --exec-command=pomerium-cli \
  --exec-arg=k8s,exec-credential,https://k8s.localhost.pomerium.io,--disable-tls-verification \
  --exec-api-version=client.authentication.k8s.io/v1beta1

Here's the resulting configuration:

1. Cluster:

   clusters:
   - cluster:
       server: https://k8s.localhost.pomerium.io
     name: via-pomerium

2. Context:

   contexts:
   - context:
       cluster: via-pomerium
       user: via-pomerium
     name: via-pomerium

3. User:

   - name: via-pomerium
     user:
       exec:
         apiVersion: client.authentication.k8s.io/v1beta1
         args:
           - k8s
           - exec-credential
           - https://k8s.localhost.pomerium.io
         command: pomerium-cli
         env: null

With kubectl configured you can now query the Kubernetes API via pomerium:

kubectl --context=via-pomerium cluster-info

You should be prompted to login and see the resulting cluster info.