This post provides an overview of the basic kubectl CLI commands that can be applied to Kubernetes objects. Some examples of Kubernetes objects include Pods, ReplicaSets, Deployments, Namespaces, etc.

Namespaces

Namespaces are used in Kubernetes to organize cluster objects. Essentially, a namespace represents a folder containing a set of objects. By default, kubectl interacts with the default namespace. To use a different namespace, the --namespace flag is required, for example --namespace=example. To interact with all namespaces, use the --all-namespaces flag ¹.

Contexts

If you want to change the default namespace permanently, you can use a context. When used, it is recorded in the kubectl configuration file, stored at HOME/.kube/config. To create a context with a new default namespace name, run ¹:

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

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kubectl config use-context my-context

Kubernetes API objects

Every Kubernetes object is represented by a RESTful resource and exists at a unique HTTP path in the Kubernetes API. Resources are represented as JSON or YAML files. Through the kubectl command, you can access these objects. For example, using kubectl get you can access any resource in the default namespace ¹:

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kubectl get <resource-name>

To get a more specific resource:

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kubectl get <resource-name> <object-name>

To get more information about the object in JSON or YAML format, you can add the -o json or -o yaml flags respectively. This output is not very human-readable.

Another option to get human-readable details about an object is to use the kubectl describe command:

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kubectl describe <resource-name> <object-name>

Creating, updating, or deleting Kubernetes objects

As mentioned earlier, Kubernetes objects or resources are represented by JSON or YAML files. To create, update, or delete these objects, such files are used. For example, to create or update an object stored in ejemplo.yaml, run:

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kubectl apply -f ejemplo.yaml

If you prefer to make interactive edits instead of modifying the local file, you can use the kubectl edit command to download the latest version and launch an editor. After saving the file, it will be uploaded and automatically updated.

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kubectl edit <resource-name> <object-name>

The kubectl apply command also saves the version history of configuration files. You can access these records using the edit-last-applied, set-last-applied, and view-last-applied options.

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kubectl apply -f myobj.yaml view-last-applied

To delete an object, simply run:

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kubectl delete -f ejemplo.yaml

Debugging

kubectl also has a set of commands for debugging your containers. To view the logs of a running container, run:

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kubectl logs <pod-name>

If there are multiple containers in the pod, you can choose the container to inspect with the -c flag.

By default, kubectl logs lists the current logs and exits. If you want to continuously stream the logs to the terminal instead, you can add the -f (follow) flag to the command line.

You can also use the exec command to run a command in a running container:

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

This will provide an interactive console inside the running container for more detailed debugging.