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The importance of kubectl in using Kubernetes is self-evident, and mastering its command line is a "required course" for many IT personnel.

While there are many articles about kubectl on the Internet, this article adheres to the principle of "concentration is the essence", simplify and then simplify, and pick out the 7 commands you will use! At the same time, it also introduces the basic syntax of the kubectl command to help you get started with kubectl!

Kubectl is a command-line tool for Kubernetes, and people usually use it to interact with Kubernetes. Through kubectl, the cluster itself can be managed, and containerized applications can be installed and deployed on the cluster. In the article "A complete tutorial on using Kubectl to manage Kubernetes," we detailed how to install kubectl in different operating systems and how to create configuration files using RKE and Rancher. In this article, we will introduce the commands that are most commonly used in kubectl.

First, let's take a look at how kubectl works:

A kubectl command can perform an action, such as get, create, or describe

An action can be performed on a resource, such as Deployment

The kubectl command follows this syntax format: kubectl an_action a_resource a_resource_name-flags

In most cases, names and logos are not necessary. For example, to get information about an existing pod, you can usually run this command directly: kubectl get pods.

Here's a tip: if you don't want to type kubectl manually every time, you can make a Bash alias. Set alias kubectlables, and then simply type "k" to replace kubectl.

Next, let's look at the most common kubectl resource types and their abbreviations (abbreviations in parentheses).

The 11 most common types of kubectl resources

Pods (po)

Nodes (no)

Deployments (deploy)

Replicasets (rs)

Daemonsets (ds)

Statefulsets (sts)

Jobs

Cronjobs (cj)

Services (svc)

Persistentvolumes (pv)

Persistentvolumeclaim (pvc)

The other names you need to know are all and event. All refers to all existing resources, and kubectl get all displays key information about running Pod, Service, Deployment, and ReplicaSet. This order is very convenient.

Similarly, kubectl get events shows the history of event. It looks like a Kubernetes-level log, not a container-level log.

If you want to see more types of kubectl resources, please refer to the official documentation:

Https://kubernetes.io/docs/reference/kubectl/overview/

Now let's take a look at common actions performed on resources.

The most commonly used kubectl command

Help- gets help

Get- displays information about one or more resources

Describe- displays detailed information about one or more resources

Logs- displays container log

Exec- enters a running process in the container

Apply- creates or selects a resource

Delete- deletes one or more resources

Now, let's take a brief look at each command.

Help

Enter-- help after the command to get help for the command. For example, kubectl get pods-help

Get

Kubectl get all shows key information about running pod, service, deployment, and Replicaset. This is the preferred command to check the status of things. You can use get with a single object and add the-watch flag to watch for updates in real time.

Describe

Kubectl describe all displays a lot of details related to your cluster, and you can also use describe with a single object. This command will be very useful in the debug process.

Logs

The logs command requires a pod name. When in multiple pod, use the-c my-container flag to specify a container. Use the-- previous flag to get container information that is no longer running.

Exec

Exec helps you debug a container process that allows you to execute processes within the container through pseudo-terminals with-it. For example, to enter the container in my_pod and run Bash, type kubectl exec-it my_pod bash.

Apply

This command can be entered through the file name or console to configure the resource. And apply can declaratively manage cluster resources: if the resource does not exist, apply will create it; if it does, apply will change it. In addition, apply can add Service to applicable resources or Deployment by adding Pod to automate auto scaling.

Note that you can use create to create a Deployment and use expose to create a Service. But relatively speaking, using a YAML file with apply is a better choice, both for the file itself and for later reuse. Apply is the "Swiss knife" that creates and updates resources.

Delete

The command kubectl delete pod my_pod can be used to delete a Pod named my_pod.

To delete all resources of the same type, you need to use the-- all flag. For example, all ReplicaSet can be deleted using kubectl delete rs-all. Please note that if you try this, delete Deployment first, otherwise ReplicaSet will restart.

Now that you know the key commands of K8s, if you want to see more kubectl commands, please refer to:

Https://kubernetes.io/docs/reference/generated/kubectl/kubectl-commands

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