Basic commands/operations in Kubernetes
Kubectl is a command-line interface that is used to run commands against the clusters of Kubernetes. It’s a CLI tool for the users through which you can communicate with the Kubernetes API server. Before running the command in the terminal, kubectl initially checks for the file name “config” and which you can see in the $HOME/.Kube directory. From a technical point of view, kubectl is a client for the Kubernetes API & from a user's point of view, it’s your cockpit to control the whole Kubernetes.
Kubectl syntax describes the command operations. To run the operations, kubectl includes the supported flags along with subcommands. And via this part of the Kubernetes series, we are going to render you some of the operations.
kubectl create −. kubectl create −. To run the operation we usually use the kubectl to create command. To do this, JSON or YAML formats are accepted.
$ kubectl create -f file_name.yaml
To specify the resources with one or more files: -f file1 -f file2 -f file...
Below is the list through which we use to create multiple things by using the kubectl command.
deployment namespace quota secret docker-registry secret secret generic secret tls serviceaccount service clusterip service loadbalancer service nodeport service nodeport
Display one or many resources, This command is capable of fetching data on the cluster about the Kubernetes resources.
List all pods in the ps output format.
List all pods in ps output format with more information (such as node name).
$ kubectl get pods -o wide
List a single replication controller with specified NAME in the ps output format.
$ kubectl get replicationcontroller web
List deployments in JSON output format, in the "v1" version of the "apps" API group:
$ kubectl get deployments.v1.apps -o json
List a pod recognized by type and name specified in "pod.yaml" in the JSON output format.
$ kubectl get -f pod.yaml -o json
Create and run a particular image, possibly replicated.
Creates a deployment or job to manage the created container(s).
Start a single instance of nginx.
$ kubectl run nginx --image=nginx
Expose a resource as a new Kubernetes service.
$ kubectl expose rc nginx --port=80 --target-port=8000
kubectl delete − Delete resources by filenames, stdin, resources and names, or by resources and label selector.
$ kubectl delete –f file_name/type_name --all
$ kubectl delete pods --all
Delete pods and services with label name=myLabel.
$ kubectl delete pods,services -l name=myLabel
Delete a pod with minimal delay
kubectl apply − It holds the capability to configure a resource by file or stdin.
$ kubectl apply –f filename
kubectl annotate − To attach metadata to Kubernetes objects, you can use either labels or annotations. As labels can be mostly used to opt the objects and to find collections of objects that satisfy certain conditions.
$ kubectl annotate created_object -f file_name resource-version _key = value $ kubectl get pods pod_name --output=yaml
kubectl autoscale − Autoscale is employed to auto-scale the pods which are specified as Deployment, replica set, Replication Controller. It also creates an autoscaler that automatically selects and sets the number of pods that runs in the Kubernetes cluster.
$ autoscale -f file_name/type [--min=MINPODS] --max=MAXPODS [--cpu-percent=CPU] $ kubectl autoscale deployment foo --min=2 --max=10
Convert 'pod.yaml' to the most advanced version and print to stdout.
The command takes filename, directory, or URL as an input, and transforms it into the format of the version defined by --output-version flag. If the target version is not specified or not supported, convert to the latest version.
$ kubectl convert -f pod.yaml
5. kubectl edit − It is applied to end the resources on the server. This allows us to directly edit a resource that one can receive via the command-line tool.
$ kubectl edit Resource/Name | File Name
Replace a resource by filename or stdin.
JSON and YAML formats are accepted. If replacing an existing resource, the complete resource spec must be provided. This can be obtained by
$ kubectl replace -f file_name
kubectl rollout − It is more competent in managing the rollout of deployment.
$ Kubectl rollout Sub_Command $ kubectl rollout undo deployment/tomcat
Apart from the above, we can perform multiple tasks using the rollout such as
View the rollout history of a deployment
$ kubectl rollout history deployment/abc
the provided resource as paused
$ kubectl rollout pause deployment/nginx
To resume a paused resource.
$ kubectl rollout resume deployment/nginx
Watch the rollout status of a deployment
$ kubectl rollout status deployment/nginx
Rollback to the previous deployment
$ kubectl rollout undo deployment/abc
kubectl scale − It will scale the dimension of Kubernetes Deployments, ReplicaSet, Replication Controller, or job.
$ kubectl scale –replica = 3 FILE_NAME
kubectl cp− Copy files and directories to and from containers.
$ kubectl cp Files_from_source Files_to_Destination $ kubectl cp /tmp/foo -pod:/tmp/bar -c specific-container
kubectl describe − Describes any appropriate resources in Kubernetes. Confers the details of a resource or an assortment of resources.
$ kubectl describe type type_name
$ kubectl describe pod/nginx
Describe a pod identified by type and name in "pod.json"
$ kubectl describe -f pod.json
Describe pods by label name=label_name
$ kubectl describe po -l name=label_name
kubectl exec− This helps to execute a command in the container.
$ kubectl exec POD -c container --command args $ kubectl exec 123-5-456 date
They are employed 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 container_name $ kubectl logs nginx
Forward one or more local ports to a pod. They are accepted to forward one or more local port to pods.
Listen on ports 5000 and 6000 locally, forwarding data to/from ports 5000 and 6000 in the pod
$ kubectl port-forward pod/mypod 5000 6000 $ kubectl port-forward tomcat 3000 4000 $ kubectl port-forward deployment/mydeployment 5000 6000
kubectl top node − It displays CPU/Memory/Storage usage. The prime or the foremost command enables you to see the resource use for the nodes.
$ kubectl top node node_name
Display metrics for all pods in the default namespace
Display metrics for all nodes
kubectl attach − Its major function is to attach things to the running container.
$ kubectl attach pod –c containers
kubectl API-versions − Basically, it prints the supported versions of API on the cluster.
kubectl cluster-info − It represents the cluster Info.
Display addresses of the master and services with label kubernetes.io/cluster-service=true
Besides, debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
Dumps cluster-info out suitable for debugging and diagnosing cluster problems. By default, dumps everything to stdout. You can optionally specify a directory with --output-directory. If you specify a directory, the Kubernetes will build an assortment of files in that directory.
By default only dumps things in the 'Kube-system' namespace, but you can shift to a different namespace with the --namespaces flag or specify --all-namespaces to dump all namespaces.
$ kubectl cluster-info dump --output-directory = /path/to/cluster-state
Modify certificate resources.
Approve/Accept a certificate signing request.
$ kubectl approve -f file_name/type
Deny a certificate signing request. This action represents a certificate signing controller to not to issue a certificate to the requestor.
$ kubectl deny -f file_name/type
kubectl drain − This is used to drain a node for preservation purposes. It makes the node for maintenance. This will mark the node as unavailable so that it should not be indicated with a new container that will be created.
$ kubectl drain node_name –force
V. KUBECTL SETTINGS AND USAGE
Print the supported API Resources
Print the supported API Resources with more information
$ kubectl api-resources -o wide
kubectl config current-context − It displays the current context.
$ kubectl config current-context
kubectl config delete-cluster − Deletes the specified cluster from kubeconfig.
$ kubectl config delete-cluster cluster_name
kubectl config delete-context − Deletes a specified context from kubeconfig.
$ kubectl config delete-context cluster_name
kubectl config get-clusters − Displays cluster defined in the kubeconfig.
$ kubectl config get-cluster $ kubectl config get-cluster cluster_name
kubectl config get-contexts − Specifies one or many contexts. Displays one or many contexts from the kubeconfig file.
$ kubectl config get-context cluster_name
Renames a context from the kubeconfig file.
CONTEXT_NAME is the context name that you wish to change.
NEW_NAME is the new name you wish to set.
$ kubectl config rename-context old_name new_name
Sets a specific value in a kubeconfig file
PROPERTY_NAME is a dot delimited name where each token implies either an attribute name or a map key. Map keys may not include dots.
PROPERTY_VALUE is the new value you wish to set. Binary fields such as 'certificate-authority-data' expect a base64 encoded string unless the --set-raw-bytes flag is used.
$ kubectl config set PROPERTY_NAME PROPERTY_VALUE
kubectl config set-cluster − Sets the cluster entry in Kubernetes.
Specifying a name that already exists will merge new fields on top of existing values for those fields.
$ kubectl config set-cluster --server=https://1.2.3.4 $ kubectl config set-cluster NAME [--server=server] [--certificate-authority=path/to/certificate/authority] [--insecure-skip-tls-verify=true]
kubectl config set-context − Sets a context entry in kubernetes entrypoint. Clarifies a name that already exists will merge new fields on top of existing values for those fields.
$ kubectl config set-context NAME [--cluster = cluster_nickname] [-- user = user_nickname] [--namespace = namespace] $ kubectl config set-context gce --user=cluster-admin
kubectl config set-credentials − Sets a user entry in kubeconfig.
Specifying a name that already exists will merge new fields on top of existing values.
Bearer token flags: --token=bearer_token
Basic auth flags: --username=basic_user --password=basic_password
$ kubectl config set-credentials cluster-admin --username = name -- password = your_password
kubectl config unset − It unsets a specific component in kubectl. PROPERTY_NAME is a dot delimited name where each token represents either an attribute name or a map key. Map keys may not hold dots.
$ kubectl config unset PROPERTY_NAME PROPERTY_VALUE
kubectl config use-context − Sets the current context in kubectl file.
$ kubectl config use-context context_name
Display merged kubeconfig settings or a specified kubeconfig file.
You can use --output jsonpath={...} to extract specific values using a JSON path expression.
Get the documentation of the resource and its fields
Get the documentation of a specific field of a resource
$ kubectl explain pods.spec.containers
Print flags inherited by all commands
Print the client and server versions for the current context
kubectl rolling-update − Operates a rolling update on a replication controller. Reinstates the specified replication controller with a new replication controller by updating a POD at a time.
$ kubectl rolling-update old_container_name new_container_name -- image = new_container_image| -f new_controller_spec $ kubectl rolling-update frontend-v1 –f freontend-v2.yaml
Kubectl syntax mentions the commands as we've explained in the foregoing section. Kubernetes is so profitable for the organizations' artistic team, for each of the project, clarifies deployments, scalability, resilience, it also permits us to consume any underlying infrastructure and you know what it proffers you much to work upon. So let's call it Supernetes from today. Good luck and stay in touch!
