Explore the diverse realms of Kubernetes (K8S) as we unveil and elucidate each frequently employed category or element. Unearth the power of kubectl commands, the Kubernetes command-line tool, designed for seamless execution of commands across Kubernetes clusters. Employ kubectl to effortlessly deploy applications, scrutinize and administer cluster resources, and peruse logs.
Delve into the intricacies of Kubernetes components, as we provide succinct descriptions sourced directly from the official documentation at kubernetes.io. For further insights or in-depth exploration, each description is accompanied by a link to the relevant documentation page.
Kubernetes Objects and Kubectl Command Cheatsheet
Cluster Management and Context
Cluster management refers to querying information about the K8S cluster itself.
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 config view -o jsonpath='{.users[*].name}' – Get a list of users.
kubectl config current-context – Display the current context.
kubectl config get-contexts – Display a list of contexts.
kubectl config use-context <cluster name> – Set the default context.
kubectl api-resources – List the API resources that are available.
kubectl api-versions – List the API versions that are available.
-A – List pods, services, daemonsets, deployments, replicasets, statefulsets, jobs, and CronJobs in all namespaces, not custom resource types. Note the alias for --all-namespaces is -A
kubectl get all --all-namespacesDaemonsets
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
Deployments – A Deployment provides declarative updates for Pods and ReplicaSets. You describe a desired state in a Deployment, and the Deployment Controller changes the actual state to the desired state at a controlled rate. You can define Deployments to create new ReplicaSets, or to remove existing Deployments and adopt all their resources with new Deployments. See StatefulSet vs. Deployment.
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 deployments on the server.
kubectl create deployment <deployment_name> – Create a new deployment.
kubectl delete deployment <deployment_name> – Delete deployments.
kubectl rollout status deployment <deployment_name> – See the rollout status of a deployment.
kubectl set image deployment/<deployment name> <container name>=image:<new image version> – Perform a rolling update (K8S default), set the image of the container to a new version for a particular deployment.
kubectl rollout undo deployment/<deployment name> – Rollback a previous deployment.
kubectl replace --force -f <configuration file> – Perform a replace deployment — Force replace, delete and then re-create the resource.
Read more about Kubernetes deployment strategies: Different Types of Kubernetes Deployment Strategies (Examples)
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 --sort-by=.metadata.creationTimestamp – List events sorted by timestamp.
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
Logs – System component logs record events happening in cluster, which can be very useful for debugging. You can configure log verbosity to see more or less detail. Logs can be as coarse-grained as showing errors within a component, or as fine-grained as showing step-by-step traces of events (like HTTP access logs, pod state changes, controller actions, or scheduler decisions).
kubectl logs <pod_name> – Print the logs for a pod.
kubectl logs --since=6h <pod_name> – Print the logs for the last 6 hours for a pod.
kubectl logs --tail=50 <pod_name> – Get the most recent 50 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 – In Kubernetes, namespaces provides a mechanism for isolating groups of resources within a single cluster. Names of resources need to be unique within a namespace, but not across namespaces. Namespace-based scoping is applicable only for namespaced objects (e.g. Deployments, Services, etc) and not for cluster-wide objects (e.g. StorageClass, Nodes, PersistentVolumes, etc).
kubectl create namespace <namespace_name> – Create a namespace.
kubectl get namespace <namespace_name> – List one or more namespaces.
kubectl describe namespace <namespace_name> – Display the detailed state of one or more namespaces.
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.
Nodes
Nodes – Kubernetes runs your workload by placing containers into Pods to run on Nodes. A node may be a virtual or physical machine, depending on the cluster. Each node is managed by the control plane and contains the services necessary to run Pods. Typically you have several nodes in a cluster; in a learning or resource-limited environment, you might have only one node. The components on a node include the kubelet, a container runtime, and the kube-proxy.
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 <node_name> – Display Resource usage (CPU/Memory/Storage) for nodes.
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 – Pods are the smallest deployable units of computing that you can create and manage in Kubernetes. A Pod (as in a pod of whales or pea pod) is a group of one or more containers, with shared storage and network resources, and a specification for how to run the containers. A Pod’s contents are always co-located and co-scheduled, and run in a shared context. A Pod models an application-specific “logical host”: it contains one or more application containers which are relatively tightly coupled. In non-cloud contexts, applications executed on the same physical or virtual machine are analogous to cloud applications executed on the same logical host. As well as application containers, a Pod can contain init containers that run during Pod startup. You can also inject ephemeral containers for debugging if your cluster offers this.
kubectl get pod – List one or more pods.
kubectl get pods --sort-by='.status.containerStatuses[0].restartCount' – List pods Sorted by Restart Count.
kubectl get pods --field-selector=status.phase=Running – Get all running pods in the namespace.
kubectl delete pod <pod_name> – Delete a pod.
kubectl describe pod <pod_name> – Display the detailed state of a pods.
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. Read more: Using Kubectl Exec: Connect to Your Kubernetes Containers
kubectl exec -it <pod_name> /bin/sh – Get an interactive shell on a single-container pod.
kubectl top pod – Display Resource usage (CPU/Memory/Storage) for pods.
kubectl annotate pod <pod_name> <annotation> – Add or update the annotations of a pod.
kubectl label pods <pod_name> new-label=<label name> – Add or update the label of a pod.
kubectl get pods --show-labels – Get pods and show labels.
kubectl port-forward <pod name> <port number to listen on>:<port number to forward to> – Listen on a port on the local machine and forward to a port on a specified pod.
Replication Controllers
Replication Controllers – Note: A Deployment that configures a ReplicaSet is now the recommended way to set up replication. A ReplicationController ensures that a specified number of pod replicas are running at any one time. In other words, a ReplicationController makes sure that a pod or a homogeneous set of pods is always up and available.
kubectl get rc – List the replication controllers.
kubectl get rc --namespace=”<namespace_name>” – List the replication controllers by namespace.
ReplicaSets
ReplicaSets – A ReplicaSet’s purpose is to maintain a stable set of replica Pods running at any given time. As such, it is often used to guarantee the availability of a specified number of identical Pods.
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
Secrets – A 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 a container image. Using a Secret means that you don’t need to include confidential data in your application code.
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
Services – An abstract way to expose an application running on a set of Pods as a network service. With Kubernetes you don’t need to modify your application to use an unfamiliar service discovery mechanism. Kubernetes gives Pods their own IP addresses and a single DNS name for a set of Pods, and can load-balance across them.
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.
Service Accounts
Service Accounts – A service account provides an identity for processes that run in a Pod.
This document serves as an introduction for users to Service Accounts, explaining how they operate in a cluster following the recommendations of the Kubernetes project. Please note that your cluster administrator may have made customizations that differ from the standard behavior described here. When a human interacts with the cluster, such as through kubectl, they are authenticated by the apiserver as a specific User Account (typically admin by default, unless customized by the cluster administrator). Similarly, processes running within containers inside pods can communicate with the apiserver and are authenticated as a specific Service Account (e.g., default).
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.
StatefulSet
StatefulSet – StatefulSet is the workload API object used to manage stateful applications. Manages the deployment and scaling of a set of Pods, and provides guarantees about the ordering and uniqueness of these Pods.
Like a Deployment, a StatefulSet manages Pods that are based on an identical container spec. Unlike a Deployment, a StatefulSet maintains a sticky identity for each of their Pods. These pods are created from the same spec, but are not interchangeable: each has a persistent identifier that it maintains across any rescheduling.
If you want to use storage volumes to provide persistence for your workload, you can use a StatefulSet as part of the solution. Although individual Pods in a StatefulSet are susceptible to failure, the persistent Pod identifiers make it easier to match existing volumes to the new Pods that replace any that have failed.
kubectl get statefulset – List StatefulSet
kubectl delete statefulset/[stateful_set_name] --cascade=false – Delete StatefulSet only (not pods).