Marco Pracucci

Kubernetes RBAC with kops

by Marco Pracucci Comments

Kops supports two authorization modes for the K8S cluster:

Create a cluster with RBAC support

When you create a new K8S cluster with kops you have to explicitly set --authorization RBAC:

kops create cluster --authorization RBAC

The newly create cluster will have the authorization mode RBAC but no default super user. To give admin user the super user privileges you should edit with cluster with kops edit cluster and then add:

  kubeAPIServer:
    authorizationRbacSuperUser: admin

Update an already existing cluster switching to RBAC

If you already have a cluster running with AlwaysAllow authorization mode and you wanna switch it to RBAC you have to edit the cluster with kops edit cluster and then edit:

  authorization:
    rbac: {}

and add the following to get the admin user having super user privileges (optional):

  kubeAPIServer:
    authorizationRbacSuperUser: admin

To apply the changes you’re required to reboot all master nodes (remember to do it one-by-one in order to not disrupt your cluster).

RBAC roles on a newly created cluster

According to this discussion on StackOverflow, some roles and bindings are required in order to get an RBAC-cluster deployed with kops working. The following should be enough to fix kube-proxy, kubelet and the default service account running in the kube-system namespace.

kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1alpha1
metadata:
  name: system:node--kubelet
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: system:node
subjects:
- kind: User
  name: kubelet
---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1alpha1
metadata:
  name: cluster-admin--kube-system:default
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: cluster-admin
subjects:
- kind: ServiceAccount
  name: default
  namespace: kube-system
---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1alpha1
metadata:
  name: system:node-proxier--kube-proxy
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: system:node-proxier
subjects:
- kind: User
  name: kube-proxy

Create an user on K8S

Kubernetes doesn’t have any “user” resource you can manage through the API. The way you create and manage users depends on how you deployed the cluster. In the case of kops, the kube-apiserver runs with --token-auth-file=/srv/kubernetes/known_tokens.csv, reading user tokens from a .csv file with the following format:

token,user,uid,"group1,group2,group3"

where groups are optional. For example:

super-secret-token,user-name,user-unique-id

To add a new user you should manually create a file in the S3 bucket used by kops to hold the state at the location secrets/USERNAME. For example, if you wanna create the user “marco” you should create the file secrets/marco containing a json with the base64 encoded user authentication token (you can generate a random token):

{"Data":"BASE64-ENCODED-TOKEN-FOR-USER-MARCO"}

To apply the changes you should reboot the masters, since at boot kops will fetch all secrets/ and generate the .csv on the fly before starting the API server.

Add an user token to kubectl config

Now that the user has been created you can add it to your ~/.kube/config:

users:
- name: marco
  user:
    token: NON-BASE64-ENCODED-TOKEN-FOR-USER-MARCO

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