Kubernetes for Developers #22: Access to Multiple Clusters or Namespaces using kubectl and kubeconfig

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In the previous article (Kubernetes for Developers #21: Kubernetes Namespace in-detail), we added name of the namespace in all kubectl commands to create or display kubernetes resources. Because kubeconfig current context referring to default namespace.

Kubeconfig file

kubeconfig file gets created automatically when you install k8 in the machine. It is usually located in the ~/.kube/config . This file contains all the necessary information to connect k8 cluster. kubectl CLI uses this file to execute commands against k8 cluster.

kubeconfig file contains four major sections
  1. clusters: it contains list of cluster details like name of the cluster, API server URL, Certificate Authority (CA) file, etc.
  2. users: it contains list of user credentials (like name, password, user token, certificate) for connecting an API server
  3. contexts: it contains combination of cluster name, user name and namespace. It is used for kubectl CLI when executing commands against k8
  4. current-context: Always one combination of context (i.e. name of cluster, user, namespace) must be set as current context.  (i.e. cluster name + user name + namespace name )


run following command to view kubeconfig file details
$ kubectl config view

apiVersion: v1
kind: Config
clusters:
  - cluster:
      certificate-authority-data: FURS0tLXX
      server: https://k8.docker.internal:6443
    name: my-k8-cluster
contexts:
  - context:
      cluster: my-k8-cluster
      user: my-test-user
      namespace: dev-ns
    name: my-test-context
users:
  - name: my-test-user
    user:
      client-certificate-data: FUEAEXX
      client-key-data: CDESXX
current-context: my-test-context


// display all contexts
$ kubectl config get-contexts
CURRENT   NAME              CLUSTER          AUTHINFO         NAMESPACE
*         my-test-context   my-k8-cluster   my-test-user      dev-ns

// display current context
$ kubectl config current-context
my-test-context

The following kubectl command display all pods from dev-ns namespace as current-context (i.e. my-test-context) referring to dev-ns namespace
// display pods
$ kubectl get po
NAME               READY   STATUS    RESTARTS   AGE
pod-nginx-dev-ns   1/1     Running   0          4m4s

run following command to modify namespace for the context
// modify namespace for the given context
$ kubectl config set-context my-test-context --namespace=dev2-ns
Context "my-test-context" modified.

// the below command display all pods from the dev2-ns namespace
$ kubectl get po
NAME               READY   STATUS    RESTARTS   AGE
pod-nginx-dev2-ns   1/1     Running   0          1m4s

Create new Context

As said earlier, every context consists of three parts
  1. Cluster details:
    2. use following kubectl command to configure new cluster details
// syntax
// kubectl config set-cluster <cluster-map-name> --server=<cluster-url> --certificate-authority=<ca-file>
$ kubectl config set-cluster my-new-cluster \
  --server=https://mycluster.k8.com:6443 \
  --certificate-authority=/path/cafile
Cluster "my-new-cluster" set.

     2. User details:
        use following kubectl command to configure new user details 
// syntax
// kubectl config set-credentials <user-map-name> --token=<user-token-info> (or)
// kubectl config set-credentials <user-map-name> --username=<username> --password=<password>
$ kubectl config set-credentials my-new-user --token=token1234abcd
User "my-new-user" set.

     3. Namespace details:
        use following kubectl command to view namespace details
// display all namespaces
$ kubectl get ns
NAME              STATUS   AGE
default           Active   31d
dev2-ns           Active   47m
dev-ns            Active   47m

Use following kubectl command to combine all above three details for creating new context
// syntax
// kubectl config set-context <context-name> \
   --cluster=<cluster-name> \
--user=<user-name> \
--namespace=<namespace-name>

$ kubectl config set-context my-new-context \
  --cluster=my-new-cluster \
  --user=my-new-user \
  --namespace=dev-ns
Context "my-new-context" created.

//display all contexts
$ kubectl config get-contexts
CURRENT   NAME             CLUSTER          AUTHINFO         NAMESPACE
*         docker-desktop   docker-desktop   docker-desktop
          my-new-context   my-new-cluster   my-new-user      dev-ns

// display current context
$ kubectl config current-context
docker-desktop

Use following kubectl command to switch the context
// change the context
$ kubectl config use-context my-new-context
Switched to context "my-new-context".

By default, the following kubectl command display all the pods from dev-ns namespace because CLI using "my-new-context" as current-context
// display pods
$ kubectl get po
NAME               READY   STATUS    RESTARTS   AGE
pod-nginx-dev-ns   1/1     Running   0          4m4s

Use following kubectl command to delete the context
// delete context
$ kubectl config delete-context my-new-context
deleted context my-new-context from ~\.kube\config

Kubernetes for Developers Journey.

Happy Coding :)

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