How to Add Users to Kubernetes (kubectl)?

Question

I've created a Kubernetes cluster on AWS with kops and can successfully administer it via kubectl from my local machine.

I can view the current config with kubectl config view as well as directly access the stored state at ~/.kube/config, such as:

apiVersion: v1
clusters:
- cluster:
    certificate-authority-data: REDACTED
    server: https://api.{CLUSTER_NAME}
  name: {CLUSTER_NAME}
contexts:
- context:
    cluster: {CLUSTER_NAME}
    user: {CLUSTER_NAME}
  name: {CLUSTER_NAME}
current-context: {CLUSTER_NAME}
kind: Config
preferences: {}
users:
- name: {CLUSTER_NAME}
  user:
    client-certificate-data: REDACTED
    client-key-data: REDACTED
    password: REDACTED
    username: admin
- name: {CLUSTER_NAME}-basic-auth
  user:
    password: REDACTED
    username: admin

I need to enable other users to also administer. This user guide describes how to define these on another users machine, but doesn't describe how to actually create the user's credentials within the cluster itself. How do you do this?

Also, is it safe to just share the cluster.certificate-authority-data?

Answer 1

For a full overview on Authentication, refer to the official Kubernetes docs on Authentication and Authorization

For users, ideally you use an Identity provider for Kubernetes (OpenID Connect).

If you are on GKE / ACS you integrate with respective Identity and Access Management frameworks

If you self-host kubernetes (which is the case when you use kops), you may use coreos/dex to integrate with LDAP / OAuth2 identity providers - a good reference is this detailed 2 part SSO for Kubernetes article.

kops (1.10+) now has built-in authentication support which eases the integration with AWS IAM as identity provider if you're on AWS.

for Dex there are a few open source cli clients as follows:

• Nordstrom/kubelogin
• pusher/k8s-auth-example

If you are looking for a quick and easy (not most secure and easy to manage in the long run) way to get started, you may abuse serviceaccounts - with 2 options for specialised Policies to control access. (see below)

NOTE since 1.6 Role Based Access Control is strongly recommended! this answer does not cover RBAC setup

EDIT: Great guide by Bitnami on User setup with RBAC is also available.

Steps to enable service account access are (depending on if your cluster configuration includes RBAC or ABAC policies, these accounts may have full Admin rights!):

EDIT: Here is a bash script to automate Service Account creation - see below steps

1. Create service account for user Alice

   kubectl create sa alice
   

2. Get related secret

   secret=$(kubectl get sa alice -o json | jq -r .secrets[].name)
   

3. Get ca.crt from secret (using OSX base64 with -D flag for decode)

   kubectl get secret $secret -o json | jq -r '.data["ca.crt"]' | base64 -D > ca.crt
   

4. Get service account token from secret

   user_token=$(kubectl get secret $secret -o json | jq -r '.data["token"]' | base64 -D)
   

5. Get information from your kubectl config (current-context, server..)

   # get current context
   c=$(kubectl config current-context)
   
   # get cluster name of context
   name=$(kubectl config get-contexts $c | awk '{print $3}' | tail -n 1)
   
   # get endpoint of current context 
   endpoint=$(kubectl config view -o jsonpath="{.clusters[?(@.name == \"$name\")].cluster.server}")
   

6. On a fresh machine, follow these steps (given the ca.cert and $endpoint information retrieved above:

   1. Install kubectl

      brew install kubectl
      

   2. Set cluster (run in directory where ca.crt is stored)

      kubectl config set-cluster cluster-staging \
        --embed-certs=true \
        --server=$endpoint \
        --certificate-authority=./ca.crt
      

   3. Set user credentials

      kubectl config set-credentials alice-staging --token=$user_token
      

   4. Define the combination of alice user with the staging cluster

      kubectl config set-context alice-staging \
        --cluster=cluster-staging \
        --user=alice-staging \
        --namespace=alice
      

   5. Switch current-context to alice-staging for the user

      kubectl config use-context alice-staging
      

To control user access with policies (using ABAC), you need to create a policy file (for example):

{
  "apiVersion": "abac.authorization.kubernetes.io/v1beta1",
  "kind": "Policy",
  "spec": {
    "user": "system:serviceaccount:default:alice",
    "namespace": "default",
    "resource": "*",
    "readonly": true
  }
}

Provision this policy.json on every master node and add --authorization-mode=ABAC --authorization-policy-file=/path/to/policy.json flags to API servers

This would allow Alice (through her service account) read only rights to all resources in default namespace only.