Grant Kubernetes service account privileges to get

Question

I would like to grant a Kubernetes service account privileges for executing kubectl --token $token get pod --all-namespaces. I'm familiar with doing this for a single namespace but don't know how to do it for all (including new ones that may be created in the future and without granting the service account full admin privileges).

Currently I receive this error message:

Error from server (Forbidden): pods is forbidden: User "system:serviceaccount:kube-system:test" cannot list resource "pods" in API group "" at the cluster scope

What (cluster) roles and role bindings are required?

UPDATE Assigning role view to the service with the following ClusterRoleBinding works and is a step forward. However, I'd like to confine the service account's privileges further to the minimum required.

kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: test
subjects:
- kind: ServiceAccount
  name: test
  namespace: kube-system
roleRef:
  kind: ClusterRole
  name: view
  apiGroup: rbac.authorization.k8s.io

The service account's token can be extracted as follows:

secret=$(kubectl get serviceaccount test -n kube-system -o=jsonpath='{.secrets[0].name}')
token=$(kubectl get secret $secret -n kube-system -o=jsonpath='{.data.token}' | base64 --decode -)

Answer 1

ClustRole & ClusterRoleBinding are correct when you need all namespaces, just shrink down the permissions:

kind: ServiceAccount
apiVersion: v1
metadata:
  name: all-ns-pod-get
  namespace: your-ns

---

kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1beta1
metadata:
  name: all-ns-pod-get
rules:
- apiGroups: [""]
  resources: ["pods"]
  verbs: ["get", "list"]

---

kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1beta1
metadata:
  name: all-ns-pod-get
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: all-ns-pod-get
subjects:
- kind: ServiceAccount
  name: all-ns-pod-get

Then all pods in a namespace your-ns will get a k8s token automatically mounted. You can use bare kubectl or k8s sdk inside a pod without passing any secrets. Note that you don't need to pass --token, just run the command in a pod within the namespace where you created that ServiceAccount.

Here's a good article explaining the concepts https://medium.com/@ishagirdhar/rbac-in-kubernetes-demystified-72424901fcb3

Answer 2

1. Follow the below yamls and create test serviceaccount.

apiVersion: v1
kind: ServiceAccount
metadata:
  name: test
  namespace: default

kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: pod-reader
rules:
- apiGroups: [""]
  resources: ["pods"]
  verbs: ["get", "list", "watch"]


kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: test
subjects:
- kind: ServiceAccount
  name: test
  namespace: default
roleRef:
  kind: ClusterRole
  name: pod-reader
  apiGroup: rbac.authorization.k8s.io

deploy test pod from the below sample

apiVersion: v1
kind: Pod
metadata:
  labels:
    run: test
  name: test
spec:
  serviceAccountName: test
  containers:
  - args:
    - sleep
    - "10000"
    image: alpine
    imagePullPolicy: IfNotPresent
    name: test
    resources:
      requests:
        memory: 100Mi

2. Install curl and kubectl

kubectl exec test apk add curl
kubectl exec test -- curl -o /bin/kubectl https://storage.googleapis.com/kubernetes-release/release/v1.12.0/bin/linux/amd64/kubectl
kubectl exec test -- sh -c 'chmod +x /bin/kubectl'

3. You should be able to list the pods from all namespaces from the test pod

master $ kubectl exec test -- sh -c 'kubectl get pods --all-namespaces'
NAMESPACE     NAME                             READY   STATUS    RESTARTS   AGE
app1          nginx-6f858d4d45-m2w6f           1/1     Running   0          19m
app1          nginx-6f858d4d45-rdvht           1/1     Running   0          19m
app1          nginx-6f858d4d45-sqs58           1/1     Running   0          19m
app1          test                             1/1     Running   0          18m
app2          nginx-6f858d4d45-6rrfl           1/1     Running   0          19m
app2          nginx-6f858d4d45-djz4b           1/1     Running   0          19m
app2          nginx-6f858d4d45-mvscr           1/1     Running   0          19m
app3          nginx-6f858d4d45-88rdt           1/1     Running   0          19m
app3          nginx-6f858d4d45-lfjx2           1/1     Running   0          19m
app3          nginx-6f858d4d45-szfdd           1/1     Running   0          19m
default       test                             1/1     Running   0          6m
kube-system   coredns-78fcdf6894-g7l6n         1/1     Running   0          33m
kube-system   coredns-78fcdf6894-r87mx         1/1     Running   0          33m
kube-system   etcd-master                      1/1     Running   0          32m
kube-system   kube-apiserver-master            1/1     Running   0          32m
kube-system   kube-controller-manager-master   1/1     Running   0          32m
kube-system   kube-proxy-vnxb7                 1/1     Running   0          33m
kube-system   kube-proxy-vwt6z                 1/1     Running   0          33m
kube-system   kube-scheduler-master            1/1     Running   0          32m
kube-system   weave-net-d5dk8                  2/2     Running   1          33m
kube-system   weave-net-qjt76                  2/2     Running   1          33m