Chapter4.md

Chapter 4. Common Kubectl Commands

Kubectl is a command line tool used for creating objects and interacting with the Kubernetes API.

Namespaces

Kubernetes uses namespaces to organize objects in the cluster. By default, kubectl interacts with default namespace but can change by using --namespace flag.

Contexts

Setting a permanent namespace in kubectl configuration file located in $HOME/.kube/config. The configuration file also stores the information of cluster for authentication and finding it. They can also be used for managing different clusters and users using --users and --clusters flags

kubectl config set-context my-context --namespace=mystuff

kubectl config use-context my-context

Viewing Kubernetes API Objects

Everything contained in Kubernetes is represented by a RESTful resource, these resources are Kubernetes objects. Each object can be called using a unique HTTP path; for example, https://your-k8s.com/api/v1/namespaces/default/pods/my-pod leads to the representation of a pod in the default namespace named my-pod. The kubectl command makes HTTP requests to these URLs to access the Kubernetes objects that reside at these paths.

kubectl get <resource-name> # listing of all resources

kubectl get <resource-name> <object-name> # specific resource, for other option use -o wide, -o json, -o yaml, --no-headers

kubectl get pods my-pod -o jsonpath --template={.status.podIP} # IP address of the pod

kubectl describe <resource-name> <object-name> # human-readable detailed  description

Creating, Updating, and Destroying Kubernetes Objects

Objects are represented as JSON or YAML files which could be used to create, update, or delete objects on the kubernetes server.

kubectl apply -f obj.yaml # everything declared in the yaml file

kubectl edit <resource-name> <object-name> # for interactive edits

kubectl delete -f obj.yaml # remove the declared resources

kubectl delete <resource-name> <object-name> # another way

Labeling and Annotating Objects

Labels and Annotation are tags for the objects which can be updated using label and annotate commands.

kubectl label pods bar color=red # label added to pod bar, for overwriting use --overwrite flag

kubectl label pods bar -color # will remove the label

Debugging Commands

kubectl logs <pod-name> # -c for particular container if pods contains multiple containers; -f for streaming logs

kubectl exec -it <pod-name> -- bash

kubectl cp <pod-name>:/path/to/remote/file /path/to/local/file # copying around host and pod

kubectl help

or

kubectl help command