Kubernetes RBAC Example

RBAC Pod Runner via ServiceAccount

Why use service account vs user? https://kubernetes.io/docs/reference/access-authn-authz/service-accounts-admin/

Simple create and delete of namespace and test service account pod that could be used as a runner

wrapper tool

https://gist.github.com/innovia/fbba8259042f71db98ea8d4ad19bd708

This example is based off of

• https://medium.com/@rschoening/read-only-access-to-kubernetes-cluster-fcf84670b698
• https://jeremievallee.com/2018/05/28/kubernetes-rbac-namespace-user.html

Use Service Account for Namespaced Admin Runner

This will create and destroy namespace test

create.sh

#!/usr/bin/env bash
set -e
# namespace=test

kubectl create namespace test
kubectl config set-context --current --namespace=test
kubectl create sa test-sa

cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: Pod
metadata:
  name: test
  namespace: test
spec:
  serviceAccountName: test-sa
  containers:
  - name: test
    image: alpine
    args:
    - sleep
    - "1000000"
EOF

sleep 5


cat <<EOF | kubectl apply -f -
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  annotations:
    rbac.authorization.kubernetes.io/autoupdate: "true"
  labels:
  name: test-read-only
  namespace: test
rules:
- apiGroups:
  - ""
  resources: ["*"]
  verbs:
  - get
  - list
  - watch
- apiGroups:
  - extensions
  resources: ["*"]
  verbs:
  - get
  - list
  - watch
- apiGroups:
  - apps
  resources: ["*"]
  verbs:
  - get
  - list
  - watch
EOF

cat <<EOF | kubectl apply -f -
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: test-binding
subjects:
- kind: ServiceAccount
  name: test-sa
  namespace: test
roleRef:
  kind: ClusterRole
  name: test-read-only
  apiGroup: rbac.authorization.k8s.io
EOF


kubectl get pod test -o yaml | grep serviceAccount

kubectl exec test -- apk add curl
kubectl exec test -- curl -L "https://dl.k8s.io/release/$(curl -L -s https://dl.k8s.io/release/stable.txt)/bin/linux/amd64/kubectl" -o /bin/kubectl
kubectl exec test -- chmod +x /bin/kubectl
kubectl exec test -- kubectl get pods
kubectl exec test -- mount | grep secrets
kubectl exec test -- ls /run/secrets/kubernetes.io/serviceaccount/
kubectl exec test -- cat /run/secrets/kubernetes.io/serviceaccount/namespace
kubectl exec test -- cat /run/secrets/kubernetes.io/serviceaccount/token
kubectl exec test -- cat /run/secrets/kubernetes.io/serviceaccount/ca.crt

delete.sh

#!/usr/bin/env bash
set -e
# namespace=test

# kubectl create namespace test
kubectl config set-context --current --namespace=test
kubectl exec test -- kubectl get pods
kubectl delete ClusterRoleBinding test-binding
sleep 15
kubectl get pods --field-selector=status.phase=Running
kubectl exec test -- kubectl get pods || true
kubectl exec test -- mount | grep secrets
kubectl exec test -- ls /run/secrets/kubernetes.io/serviceaccount/
kubectl delete clusterrole test-read-only
kubectl delete sa test-sa
kubectl delete pod test
kubectl delete namespace test

Extract creds via command if wanted

s=$(kubectl describe sa test-sa | grep Tokens | awk '{print $2}'); kubectl get secret $s   -o "jsonpath={.data['ca\.crt']}"
s=$(kubectl describe sa test-sa | grep Tokens | awk '{print $2}'); kubectl get secret $s   -o "jsonpath={.data['ca\.crt']}"

kubectl exec test -- ls /run/secrets/kubernetes.io/serviceaccount/
kubectl exec test -- cat /run/secrets/kubernetes.io/serviceaccount/namespace
kubectl exec test -- cat /run/secrets/kubernetes.io/serviceaccount/token
kubectl exec test -- cat /run/secrets/kubernetes.io/serviceaccount/ca.crt

https://kubernetes.io/docs/tasks/configure-pod-container/configure-service-account/