Kubernetes Cheat Sheet Tutorial

This Kubernetes cheat sheet is prepared by our experts keeping in mind those learners who have started learning Kubernetes as a tool. This cheat sheet will be a handy reference for them when they start implementing what they have learned in real-life problems. In this Kubernetes cheat sheet, you get a quick reference to all the basics that you must know about Kubernetes.

What is Kubernetes?

Kubernetes is an open-source platform used to automate deployment and to scale containers across clusters of hosts providing container-centric infrastructure.

• It is a container orchestrator.
• It can run a Linux container.
  • Launches a container
  • Maintains and monitors the container site
  • Performs container-oriented networking

Architecture/Interaction

Key Concepts

Now, let’s discuss the key points of this architecture.

• Pod: Group of containers
• Label: Used to identify pods
• Kubelet: Container agents, responsible for maintaining the set of pods
• Proxy: The load balancer for pods, helping in distributing tasks across them
• Etcd: A metadata service
• CAdvisor: Used for monitoring resource usage and performance
• Replication controller: Manages pod replication
• Scheduler: Used for pod scheduling in worker nodes
• API server: Kubernetes API server

Now, let’s understand the roles master and worker nodes play in the Kubernetes architecture.

Master Node

• It is responsible for maintaining the desired state of the cluster we are working on.
• The term ‘master‘ indicates a set of processes that are used to manage a cluster.
• It contains Kubelet service info, API, scheduler, replication controller, and Kubernetes master.

Worker Nodes/Minions

Also called a ‘minion,’ a worker node contains the services necessary to run the pods that are managed by the master.

• Services it provides are Container Runtime, Kubelet, Kube-proxy, etc.
• It contains Kubelet, cAdvisor, Services, Pods, and Containers.

Moving forward, let’s check out the important commands used in Kubernetes.

Kubectl Commands

For Pods and Container Introspection

Command	Function
Kubectl get pods	Lists all current pods
Kubectl describe pod<name>	Describes pod names
Kubectl get rc	Lists all replication controllers
Kubectl get rc –namespace=”namespace”	Lists replication controllers in a namespace
Kubectl describe rc <name>	Shows the replication controller name
Kubectl get cvc	Lists services
Kubectl describe svc<name>	Shows a service name
Kubectl delete pod<name>	Deletes a pod
Kubectl get nodes -w	Watches nodes continuously

For Debugging

Function	Command
To execute the command on service by selecting a container	Kubectl exec<service><commands>[-c< $container>]
To get logs from the service for a container	Kubectl logs -f<name>>[-c< $container>]
To watch kubelet logs	Watch -n 2 cat/var/log/kublet.log
To show metrics for a node	Kubectl top node
To show metrics for a pod	Kubectl top pod

For Cluster Introspection

Function	Command
To get version-related information	Kubectl version
To get cluster-related information	Kubectl cluster-info
To get configuration details	Kubectl config g view
To get information about a node	Kubectl describe node<node>

Objects

Some of the common objects used in Kubernetes are mentioned in the below table:

All	cluster role bindings	clusterroles
cm= conf gmaps	controller revisions	crd=custom resource definition
Cronjobs	cs=component statuses	csr= certificate signing requests
Deploy=deployments	ds= daemon sets	ep=end points
ev= events	hpa= horizontal pod autoscaling	ing= ingress
jobs	limits=limit ranges	Netpol- network policies
No = nodes	ns= namespaces	pdb= pod distribution budgets
po= pods	Pod preset	Pod templates
Psp= pod security policies	Pv= persistent volumes	pvc= persistent volume claims
quota= resource quotas	rc= replication controllers	Role bindings
roles	rs= replica sets	sa= service accounts
sc= storage classes	secrets	sts= stateful sets

Other Quick Commands

Additionally, we do have some quick commands that are often very useful:

Function	Command
To launch a pod with a name and an image	Kubectl run<name> — image=<image-name>
To create a service described in <manifest.yaml>	Kubectl create -f <manifest.yaml>
To scale the replication counter to count the number of instances	Kubectl scale –replicas=<count>rc<name>
To map the external port to the internal replication port	Expose rc<name> –port=<external>–target-port=<internal>
To stop all pods in <n>	Kubectl drain<n>– delete-local-data–force–ignore-daemonset
To create a namespace	Kubectl create namespace <namespace>
To allow the master node to run pods	Kubectl Taint Nodes –all-node-role.kuernetes.io/master-

Features of Kubernetes

• Automated scheduling: It provides an advanced scheduler that helps launch containers on cluster nodes.
• Self-healing: Rescheduling, replacing, and restarting of dead containers are possible.
• Automated rollouts and rollbacks: It supports rollback for systems in the case of failures and enables rollout and rollback for the desired state.
• Horizontal scaling: It can be scaled up and down as required and can be automated with respect to the CPU usage.
• Service discovery and load balancing: It uses a unique IP and DNS name for containers that helps in identifying them.

Kubectl is the command line utility to interact with Kubernetes API. It is an interface which is used to communicate and manage pods in Kubernetes cluster.

One needs to set up kubectl to local in order to interact with Kubernetes cluster.

Setting Kubectl

Download the executable to the local workstation using the curl command.

On Linux

On OS X workstation

After download is complete, move the binaries in the path of the system.

Configuring Kubectl

Following are the steps to perform the configuration operation.

• Replace ${MASTER_HOST} with the master node address or name used in the previous steps.
• Replace ${CA_CERT} with the absolute path to the ca.pem created in the previous steps.
• Replace ${ADMIN_KEY} with the absolute path to the admin-key.pem created in the previous steps.
• Replace ${ADMIN_CERT} with the absolute path to the admin.pem created in the previous steps.

Verifying the Setup

To verify if the kubectl is working fine or not, check if the Kubernetes client is set up correctly.

Kubectl controls the Kubernetes Cluster. It is one of the key components of Kubernetes which runs on the workstation on any machine when the setup is done. It has the capability to manage the nodes in the cluster.

Kubectl commands are used to interact and manage Kubernetes objects and the cluster. In this chapter, we will discuss a few commands used in Kubernetes via kubectl.

kubectl annotate −

It updates the annotation on a resource.

For example,

kubectl annotate pods tomcat description = ‘my frontend’

kubectl api-versions −

It prints the supported versions of API on the cluster.

kubectl apply −

It has the capability to configure a resource by file or stdin.

kubectl attach −

This attaches things to the running container.

kubectl autoscale −

This is used to auto scale pods which are defined such as Deployment, replica set, Replication Controller.

kubectl cluster-info −

It displays the cluster Info.

kubectl cluster-info dump −

It dumps relevant information regarding cluster for debugging and diagnosis.

kubectl config −

Modifies the kubeconfig file.

kubectl config current-context −

It displays the current context.

kubectl config delete-cluster −

Deletes the specified cluster from kubeconfig.

kubectl config delete-context −

Deletes a specified context from kubeconfig.

kubectl config get-clusters −

Displays cluster defined in the kubeconfig.

kubectl config get-contexts −

Describes one or many contexts.

kubectl config set-cluster −

Sets the cluster entry in Kubernetes.

path/to/certificate/authority] [–insecure-skip-tls-verify = true]

kubectl config set-context −

Sets a context entry in kubernetes entrypoint.

kubectl config set-credentials −

Sets a user entry in kubeconfig.

kubectl config set −

Sets an individual value in kubeconfig file.

kubectl config unset −

It unsets a specific component in kubectl.

kubectl config use-context −

Sets the current context in kubectl file.

kubectl config view

kubectl cp −

Copy files and directories to and from containers.

kubectl create −

To create resource by filename of or stdin. To do this, JSON or YAML formats are accepted.

In the same way, we can create multiple things as listed using the create command along with kubectl.

• deployment
• namespace
• quota
• secret docker-registry
• secret
• secret generic
• secret tls
• serviceaccount
• service clusterip
• service loadbalancer
• service nodeport

kubectl delete −

Deletes resources by file name, stdin, resource and names.

kubectl describe −

Describes any particular resource in kubernetes. Shows details of resource or a group of resources.

kubectl drain −

This is used to drain a node for maintenance purpose. It prepares the node for maintenance. This will mark the node as unavailable so that it should not be assigned with a new container which will be created.

kubectl edit −

It is used to end the resources on the server. This allows to directly edit a resource which one can receive via the command line tool.

Ex.

kubectl exec −

This helps to execute a command in the container.

kubectl expose −

This is used to expose the Kubernetes objects such as pod, replication controller, and service as a new Kubernetes service. This has the capability to expose it via a running container or from a yaml file.

kubectl get −

This command is capable of fetching data on the cluster about the Kubernetes resources.

For example,

kubectl logs −

They are used to get the logs of the container in a pod. Printing the logs can be defining the container name in the pod. If the POD has only one container there is no need to define its name.

$ kubectl logs [-f] [-p] POD [-c CONTAINER]

Example

kubectl port-forward −

They are used to forward one or more local port to pods.

kubectl replace −

Capable of replacing a resource by file name or stdin.

kubectl rolling-update − Performs a rolling update on a replication controller. Replaces the specified replication controller with a new replication controller by updating a POD at a time.

kubectl rollout −

It is capable of managing the rollout of deployment.

Apart from the above, we can perform multiple tasks using the rollout such as −

• rollout history
• rollout pause
• rollout resume
• rollout status
• rollout undo

kubectl run −

Run command has the capability to run an image on the Kubernetes cluster.

kubectl scale −

It will scale the size of Kubernetes Deployments, ReplicaSet, Replication Controller, or job.

kubectl set image −

It updates the image of a pod template.

kubectl set resources −

It is used to set the content of the resource. It updates resource/limits on object with pod template.

kubectl top node −

It displays CPU/Memory/Storage usage. The top command allows you to see the resource consumption for nodes.

The same command can be used with a pod as well.