kubectl
Kubectl is the command line configuration tool to interact with Kubernetes clusters using Kubernetes API server. kubectl allows users to create, inspect, update, and delete Kubernetes objects.
Kubectl Characteristics
Kubectl can be pronounced as “cube CTL”, “kube control”, “cube cuttle”
It is a is a robust CLI that runs commands against the Kubernetes cluster and controls the cluster manager
kubectl is known as the swiss army knife of container orchestration and management
kubectl is designed to make this process more comfortable and straightforward
kubectl allows users to create, inspect, update, and delete Kubernetes objects
Every Kubernetes command has an API endpoint, and kubectl’s primary purpose is to carry out HTTP requests to the API.
Most Common Kubectl Commands:
Cluster Management: A Kubernetes cluster is a set of nodes that run containerized applications. It allows containers to run across multiple machines and environments: virtual, physical, cloud-based, and on-premises. Following kubectl commands can be used to manage a cluster
kubectl cluster-info : Display endpoint information about the master and services in the cluster
kubectl version : Display the Kubernetes version running on the client and server
kubectl config view : Get the configuration of the cluster
kubectl api-resource : List the API resources that are available
kubectl api-versions : List the API versions that are available
kubectl get all –all -namespaces : List everything
Listing Resources: Kubernetes resources also known as Kubernetes objects associated to a specific namespace, you can either use individual kubectl get command to list down each resource one by one, or you can list down all the resources in a Kubernetes namespace by running a single command. Following are the list of commands to get the resources information.
kubectl get namespaces : Generate a plain-text list of all namespaces:
kubectl get pods : Generate a plain-text list of all pods
kubectl get pods -o wide : Generate a detailed plain-text list of all pods
kubectl get pods–field-selector=spec. nodeName=[server-name] : Generate a list of all pods running on a particular node server
kubectl get replicationcontroller [replication-controller-name] : List a specific replication controller in plain text
kubectl get replicationcontroller, services : Generate a plain-text list of all replication controllers and services
Daemonsets : A Daemonset ensures that all (or some) Nodes run a copy of a Pod. As nodes are added to the cluster, Pods are added to them. As nodes are removed from the cluster, those Pods are garbage collected. Deleting a DaemonSet will clean up the Pods it created.
kubectl get daemonset : List one or more daemonsets
kubectl edit daemonset <daemonset_name> : Edit and update the definition of one or more daemonset
kubectl delete daemonset <daemonset_name> : Delete a daemonset
kubectl create daemonset <daemonset_name> : Create a new daemonset
kubectl rollout daemonset : Manage the rollout of a daemonset
kubectl describe ds <daemonset_name> -n <namespace_name> : Display the detailed state of daemonsets within a namespace
Deployments : A Kubernetes Deployment is used to tell Kubernetes how to create or modify instances of the pods that hold a containerized application. Deployments can scale the number of replica pods, enable rollout of updated code in a controlled manner, or roll back to an earlier deployment version if necessary.
kubectl get deployment : List one or more deployments
kubectl describe deployment <deployment_name> : Display the detailed state of one or more deployments
kubectl edit deployment <deployment_name> : Edit and update the definition of one or more deployment on the server
kubectl create deployment <deployment_name> : Create one a new deployment
kubectl delete deployment <deployment_name> : Delete deployments
kubectl rollout status deployment <deployment_name> : See the rollout status of a deployment
Events: Kubernetes events are objects that show you what is happening inside a cluster, such as what decisions were made by the scheduler or why some pods were evicted from the node. Events are the first thing to look at for application, as well as infrastructure operations when something is not working as expected. Following are the kubectl commands to get the events.
kubectl get events : List recent events for all resources in the system
kubectl get events –field-selector type=Warning : List Warnings only
kubectl get events –field-selector involvedObject.kind!=Pod : List events but exclude Pod events
kubectl get events –field-selector involvedObject.kind=Node, involvedObject.name=<node_name> : Pull events for a single node with a specific name
kubectl get events –field-selector type!=Normal : Filter out normal events from a list of events
Logs : Kubernets logs commands can be used to monitor, logging and debugging the pods.
kubectl logs <pod_name> : Print the logs for a pod
kubectl logs –since=1h <pod_name> : Print the logs for the last hour for a pod
kubectl logs –tail=20 <pod_name> : Get the most recent 20 lines of logs
kubectl logs -f <service_name> [-c <$container>] : Get logs from a service and optionally select which container
kubectl logs -f <pod_name> : Print the logs for a pod and follow new logs
kubectl logs -c <container_name> <pod_name> : Print the logs for a container in a pod
kubectl logs <pod_name> pod.log : Output the logs for a pod into a file named ‘pod.log’
kubectl logs –previous <pod_name> : View the logs for a previously failed pod
Namespaces : Namespaces are Kubernetes objects which partition a single Kubernetes cluster into multiple virtual clusters. Each Kubernetes namespace provides the scope for Kubernetes Names it contains; which means that using the combination of an object name and a Namespace, each object gets an unique identity across the cluster.
kubectl create namespace <namespace_name> : Create namespace <name>
kubectl get namespace <namespace_name> : List one or more namespaces
kubectl describe namespace <namespace_name> : Display the detailed state of one or more namespace
kubectl delete namespace <namespace_name> : Delete a namespace
kubectl edit namespace <namespace_name> : Edit and update the definition of a namespace
kubectl top namespace <namespace_name> : Display Resource (CPU/Memory/Storage) usage for a namespace
Node Operations: A Node is a worker machine in Kubernetes and may be either a virtual or a physical machine, depending on the cluster. Each Node is managed by the control plane. A Node can have multiple pods, and the Kubernetes control plane automatically handles scheduling the pods across the Nodes in the cluster. Following commands can be used for Node Operations.
kubectl taint node <node_name> : Update the taints on one or more nodes
kubectl get node : List one or more nodes
kubectl delete node <node_name> : Delete a node or multiple nodes
kubectl top node : Display Resource usage (CPU/Memory/Storage) for nodes
kubectl describe nodes | grep Allocated -A 5 : Resource allocation per node
kubectl get pods -o wide | grep <node_name> : Pods running on a node
kubectl annotate node <node_name> : Annotate a node
kubectl cordon node <node_name> : Mark a node as unschedulable
kubectl uncordon node <node_name> : Mark node as schedulable
kubectl drain node <node_name> : Drain a node in preparation for maintenance
kubectl label node : Add or update the labels of one or more nodes
Pods : Pods are the atomic unit on the Kubernetes platform. When we create a Deployment on Kubernetes, it creates Pods with containers inside them. Each Pod is tied to the Node where it is scheduled and remains there until termination or deletion or restarted. Following kubectl command can be used for Pods Operations.
kubectl get pod : List one or more pods
kubectl delete pod <pod_name> : Delete a pod
kubectl create pod <pod_name> : Create a pod
kubectl exec <pod_name> -c <container_name> <command> : Execute a command against a container in a pod
kubectl exec -it <pod_name> /bin/sh : Get interactive shell on a a single-container pod
kubectl top pod : Display Resource usage (CPU/Memory/Storage) for pods
kubectl describe pod <pod_name> : Display the detailed state of a pods
kubectl annotate pod <pod_name> <annotation> : Add or update the annotations of a pod
kubectl label pod <pod_name> : Add or update the label of a pod
Replication Controllers and ReplicaSets
kubectl get rc : List the replication controllers
kubectl get rc –namespace=”<namespace_name>” : List the replication controllers by namespace
kubectl get replicasets : List ReplicaSets
kubectl describe replicasets <replicaset_name> : Display the detailed state of one or more ReplicaSets
kubectl scale –replicas=[x] : Scale a ReplicaSet
Secrets: A Kubernets Secret is an object that contains a small amount of sensitive data such as a password, a token, or a key. Such information might otherwise be put in a Pod specification or in an image. Users can create Secrets and the system also creates some Secrets using following kubectl commands.
kubectl create secret : Create a secret
kubectl get secrets : List secrets
kubectl describe secrets : List details about secrets
kubectl delete secret <secret_name> : Delete a secret
Services and Service Accounts: A Kubernetes service is a logical abstraction for a deployed group of pods in a cluster (which all perform the same function) and Service accounts are used to provide an identity for pods. Pods that want to interact with the API server will authenticate with a particular service account.
kubectl get services : List one or more services
kubectl describe services : Display the detailed state of a service
kubectl expose deployment [deployment_name] : Expose a replication controller, service, deployment or pod as a new Kubernetes service
kubectl edit services : Edit and update the definition of one or more services
kubectl get serviceaccounts : List service accounts
kubectl describe serviceaccounts : Display the detailed state of one or more service accounts
kubectl replace serviceaccount : Replace a service account
kubectl delete serviceaccount <service_account_name> : Delete a service account
kubectl get pod |grep -P ‘\s+([1–9]+)\/\1\s+’ : List Pods in Ready Status
kubectl get pod |grep -Pv ‘\s+([1–9]+)\/\1\s+’ : List Pods which are not Ready/Pending status
kubectl get pods -n namespacesort - -sort by=.metadata.creationTimestamp : List Pods by Deployment timestamp (add -A for live listing)
kubectl get deployment -n namespace -o=jsonpath=”{range .items[*]}{‘\n’}{.metadata.name}{‘:\t’}{range .spec.template.spec.containers[*]}{.image}{‘, ‘}{end}{end}” : List deployment Artifact/ Images in current namespace.
kubectl get deployment <deployment_name> -o=jsonpath=’{$.spec.template.spec.containers[:1].image}’ : Get Image version of current deployment.
kubectl get pod <mutlti_conatiner_pod> -o go-template=’{{range .status.containerStatuses}}{{printf “%s:\n%s\n\n” .name .lastState.terminated.message}}{{end}}’ : List last terminated Status
kubectl logs <pod_name> <conatiner_name> -n namespace - -previous / kubectl logs - -previous ${POD_NAME} ${CONTAINER_NAME} : List logs of previous state
kubectl logs - -selector app=<app_name> - -container <conatiner_name> : Multi Pod logs
kubectl -n logs -f deployment/ - -all-containers=true - -since=10m : list logs for last 10 mis
kubectl rollout history deployment/app : Inspect the history of your Deployment
kubectl rollout undo deployment/app - -to-revision=2 : Rollback to a specific version
kubectl rollout undo deployment/<deployment_name> : Rollback deployment to last version.
kubectl rollout restart -n namespace deployment/<deployment_name>: Restart deployment.
kubectl describe pod | grep ‘Name:\| Limits\| Requests\| cpu:\| memory’ : List Memory and CPU limit of pod, replace pod with deployment to list deployment wise resource limits.
kubectl delete pod - -selector=project.app=<app_name> -n namespace : Delete multiple pods with single command for a deployment.
kubectl delete pod <pod_name> -n namespace - -grace-period=0 - -force : Force delete the pod
Kubectl top pod : List down Pod resources CPU and Memory
kubectl top pod <pod_name> - -containers : List Container wise resource usage
Kubectl top node : List Node resource usage.
kubectl exec -it <pod_name> sh : Shell into the pod
kubectl exec -it <pod_name> - -/bin/bash : bash into the pod
kubectl edit ingress <ingress_name> -n namespace : edit ingress file
kubectl create secret generic <secret_name> - -from-literal=Key=value - -from-literal=Key=User: create a secret file at cluster level and keep adding - -from=literal for all Key values. example kubectl create secret generic <secret_name> - -from-literal=DB_name=ExampleDB - -from-literal=DB_password=Ahdgakah
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