9_accessing_multiple_clusters.md

Organizing Cluster Access Using kubeconfig Files

• The kubectl command-line tool uses kubeconfig files to find the information it needs to choose a cluster and communicate with the API server of a cluster.

• By default, kubectl looks for a file named config in the $HOME/.kube directory. You can specify other kubeconfig files by setting the KUBECONFIG environment variable or by setting the --kubeconfig flag.

• The file contains three main sections, clusters, users, and contexts, each with its own specific information:

  1. clusters
     Define the Kubernetes cluster being accessed, including the API server URL, certificate authorities, and other cluster-specific details.

  2. users
     Provide the authentication details for the existing user or application accessing the Kubernetes cluster. This can include a username and password, client certificates, or authentication tokens.

  3. contexts
     Define the environment for the user or application interacting with the Kubernetes cluster.
     It specifies the cluster being accessed, the user credentials being used, and the namespace being targeted.
     Multiple contexts can be defined in the kubeconfig file, allowing for easy switching between different environments or clusters.

The loading order follows these rules:

1. If the --kubeconfig flag is set, then only that file is loaded. The flag may only be set once and no merging takes place.
   
2. If $KUBECONFIG environment variable is set, then it is used as a list of paths (normal path delimiting rules for your system). These paths are merged. When a value is modified, it is modified in the file that defines the stanza. When a value is created, it is created in the first file that exists. If no files in the chain exist, then it creates the last file in the list.
3. Otherwise, ${HOME}/.kube/config is used and no merging takes place.
   

kubectl config current-context
kubectl config set-context
kubectl config use-context
kubectl config delete-context