This is my ~/.kube/config file:

apiVersion: v1
clusters:
- cluster:
    server: https://192.168.10.190:6443
  name: cluster-1
- cluster:
    server: https://192.168.99.101:8443
  name: cluster-2
contexts:
- context:
    cluster: cluster-1
    user: kubernetes-admin-1
  name: cluster-1
- context:
    cluster: cluster-2
    user: kubernetes-admin-2
  name: cluster-2
kind: Config
preferences: {}
users:
- name: kubernetes-admin-1
  user:
    client-certificate: /home/user/.minikube/credential-for-cluster-1.crt
    client-key: /home/user/.minikube/credential-for-cluster-1.key
- name: kubernetes-admin-2
  user:
    client-certificate: /home/user/.minikube/credential-for-cluster-2.crt
    client-key: /home/user/.minikube/credential-for-cluster-2.key

---

My understanding is, cluster-1 & cluster-2 are kubernetes physical clusters (Control Plane).

Each physical cluster has multiple virtual clusters (Namespaces)

If my understanding is correct, then with the above kubeConfig, What is the kubectl syntax to get all the namespaces in cluster?

CodePudding user response：

In kubernetes there is no such thing as physical or virtual cluster. Kubeconfig consists of three parts.

• clusters
• users
• contexts

1. clusters - k8s clusters made of different VMs/on-prem nodes
2. users - users that have access to the cluster, it can be the kube-admin or a normal developer. user can have roles that define what resources can the user manipulate (RBAC)
3. contexts - a link between one cluster and one user, because you work with one cluster as a user.

Now for namespaces, they work like linux network namespaces. think of it as a house with a family living inside. If you have a Bob Newman in the house you living in, you would simply call him Bob. If the bob would be living in another house, you would reference him as Bob Newman. Namespaces logically split resources inside the cluster. You can have e.g. monitoring namespace, payroll namespace, backend namespace. The house has different

CodePudding user response：

Hope this answer helps you:

Manage multiple clusters with Contexts

Let's say we have multiple clusters to administrator, so we have multiple kubeconfig file.

But it's not so efficent to use --kubeconfig option everytime with our kubectl command!

---

Access multiple clusters using Contexts

• Define all the clusters and users in the 1 kubeconfig file
• Define a context for each cluster
• We can switch between clusters using these contexts
• No need to specify kube konfig file

---

What is a Contexts?

In a kubeconfig file, we have:

• List of K8s clusters
• List of K8s users
• Names to reference them inside the kubeconfig file
• And also we have Context

Context

• Combination of which user should access which cluster
• Or "Use the credentials of the kubernetes-admin user to access the kubernetes cluster"
• We interact with it via either:
  • Update kubeconfig manually
  • or Use kubectl config commands

---

• How to switch the context?

  kubectl config use-context <CONTEXT-NAME>
  

• Display list of contexts

  kubectl config get-context
  

• Display the current-context

  kubectl config gcurrent-context
  

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Namespaces in Contexts

Each context consists actually 3 components

• cluster
• user
• namespace
• By default, the default namespace is configured
• Other than default namespace, we need to define them

Lets say most of the time, we work with 1 specific namespace (other than default) and its kind of annoying to use --namespace for each kubectl command...

• Switch default namespace

  kubectl config set-context --current --namespace kube-system
  

• Now check the ~/.kube/config file

  contexts:
  - context:
      cluster: kubernetes
      namespace: kube-system # Just added!
      user: kubernetes-admin
    name: kubernetes-admin@kubernetes
  

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kubernetes-namespaces