Kubernetes - Kubectl Commands

Pre-requisites: Kubernetes 

The Kubernetes command-line tool, kubectl, allows you to run commands against Kubernetes clusters. You can use kubectl to deploy applications, inspect and manage cluster resources, and view logs. Some basic Kubectl commands in a Kubernetes cluster are as follows:

kubectl Commands 

The most popular kubectl commands and flags are listed below.

1. Common Commands 

2. Check Performance

3. Label & Annontation

4.  Secrets 

5. Service

6. Volumes & Volume Claims

Kubectl apply

We can update or apply the configuration to a cluster with the aid of "kubectl apply". With the help of the apply command, Kubernetes resources can be modified and created using a configuration file or a collection of configurations from a directory. 

Creating objects: The basic syntax of "kubectl apply"

kubectl apply -f <filename.yaml> 

Viewing and Finding Resources

These commands are used to show all the resources. It works like a READ operation. It is used to view resources like nodes, deployments, services, config maps, etc. 

$ kubectl get <resource>

• Getting all Resources: The "kubectl get all" command enables us to view all of the cluster's resource

• Getting  Nodes: The number of available nodes in the cluster will be displayed by "Kubectl get nodes". 

• Getting Pods: "Kubectl get pod" can be used to find out how many pods are scheduled in the cluster.

• Getting Services: "Kubectl get service" can be used to list the services that have been created in the cluster.

Creating Resources

These commands are used to create resources like deployments, services, secrets, config maps, etc.

$ kubectl create <resource_type> <resource_name> OPTIONS

• Creating Deployment: The command creates a deployment named nginx-depl using the image Nginx.

• Creating service: The command in the creates a service of type node port named nginx and it is exposed on port 80 of the local machine

Editing Resources

After running the command below you can update the resource configuration file and if there are any changes the resource will be updated according to it.

kubectl edit <resource_type> <resource_name>

• Updating Deployment: The command in the below output opens a Vim-like editor in the terminal to edit the Nginx-deal deployment config file.

• Updating Service: The command opens a vim-like editor in the terminal to edit the Nginx service config file.

Deleting Resources

These commands are used to delete resources like deployments, services, config maps, pods, secrets, etc. You can choose a particular resource name of a resource type or you can also delete all resources of a resource type by specifying --all flag

kubectl delete <resource_type> <resource_name> | --all

• Deleting Deployment: The command deletes a deployment named nginx-depl.

• Deleting Service: The command deletes a service named Nginx.

Using Configuration File for CRUD

These commands are used to use YAML configuration files for CRUD operations in a cluster.

• Applying a Config file: The command creates the resource if it does not exist or updates it if it already exists according to the configuration in the YAML file mentioned after the -f flag.

$ kubectl apply -f [file-name]

• Deleting using Config file: The command deletes the resource that was created using the YAML config file mentioned after the -f flag/ 

$ kubectl delete -f [file-name]

Interacting with running Pods

• Viewing Logs of a Pod: The command shows the logs of the pod mentioned once the pod started.

$ kubectl logs [pod-name]

• Get an Interactive terminal for a pod: The command starts an interactive terminal of the Nginx pod so that we can control the pod directly through its terminal.

$ kubectl exec -it [pod-name] -- bin/bash

• Get info about a Resource: The command gives details about the nginx deployment

$ kubectl describe <resource_type> [resource-name]

Copying Files and Directories to and from Containers

With the help of the "kubectl cp" command, we can copy files from host to container and vice versa.

The basic syntax of "kubectl  cp"

kubectl cp <host path pod name:container path> 

This command will only function if the "tar" command in the container images is present or the command failed to run. 

Updating Resources

The "kubectl get rs" command allows us to check the list of deployments, To update them, look up the revision history of prior deployments, and roll back to a specific revision if necessary. Using the following commands. 

kubectl rollout <history> , <undo> , <status>, <restart>