Learn Kubernetes Basics

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Overview of kubectl

Kubectl is a command line interface for running commands against Kubernetes clusters. kubectl looks for a file named config in the $HOME/.kube directory. You can specify other kubeconfig files by setting the KUBECONFIG environment variable or by setting the --kubeconfig flag.

This overview covers kubectl syntax, describes the command operations, and provides common examples. For details about each command, including all the supported flags and subcommands, see the kubectl reference documentation. For installation instructions see installing kubectl.

Syntax

Use the following syntax to run kubectl commands from your terminal window:

kubectl [command] [TYPE] [NAME] [flags]

where command, TYPE, NAME, and flags are:

When performing an operation on multiple resources, you can specify each resource by type and name or specify one or more files:

Caution: Flags that you specify from the command line override default values and any corresponding environment variables.

If you need help, just run kubectl help from the terminal window.

Operations

The following table includes short descriptions and the general syntax for all of the kubectl operations:

Operation Syntax Description
annotate kubectl annotate (-f FILENAME \| TYPE NAME \| TYPE/NAME) KEY_1=VAL_1 ... KEY_N=VAL_N [--overwrite] [--all] [--resource-version=version] [flags] Add or update the annotations of one or more resources.
api-versions kubectl api-versions [flags] List the API versions that are available.
apply kubectl apply -f FILENAME [flags] Apply a configuration change to a resource from a file or stdin.
attach kubectl attach POD -c CONTAINER [-i] [-t] [flags] Attach to a running container either to view the output stream or interact with the container (stdin).
autoscale kubectl autoscale (-f FILENAME \| TYPE NAME \| TYPE/NAME) [--min=MINPODS] --max=MAXPODS [--cpu-percent=CPU] [flags] Automatically scale the set of pods that are managed by a replication controller.
cluster-info kubectl cluster-info [flags] Display endpoint information about the master and services in the cluster.
config kubectl config SUBCOMMAND [flags] Modifies kubeconfig files. See the individual subcommands for details.
create kubectl create -f FILENAME [flags] Create one or more resources from a file or stdin.
delete kubectl delete (-f FILENAME \| TYPE [NAME \| /NAME \| -l label \| --all]) [flags] Delete resources either from a file, stdin, or specifying label selectors, names, resource selectors, or resources.
describe kubectl describe (-f FILENAME \| TYPE [NAME_PREFIX \| /NAME \| -l label]) [flags] Display the detailed state of one or more resources.
diff kubectl diff -f FILENAME [flags] Diff file or stdin against live configuration (BETA)
edit kubectl edit (-f FILENAME \| TYPE NAME \| TYPE/NAME) [flags] Edit and update the definition of one or more resources on the server by using the default editor.
exec kubectl exec POD [-c CONTAINER] [-i] [-t] [flags] [-- COMMAND [args...]] Execute a command against a container in a pod.
explain kubectl explain [--recursive=false] [flags] Get documentation of various resources. For instance pods, nodes, services, etc.
expose kubectl expose (-f FILENAME \| TYPE NAME \| TYPE/NAME) [--port=port] [--protocol=TCP\|UDP] [--target-port=number-or-name] [--name=name] [--external-ip=external-ip-of-service] [--type=type] [flags] Expose a replication controller, service, or pod as a new Kubernetes service.
get kubectl get (-f FILENAME \| TYPE [NAME \| /NAME \| -l label]) [--watch] [--sort-by=FIELD] [[-o \| --output]=OUTPUT_FORMAT] [flags] List one or more resources.
label kubectl label (-f FILENAME \| TYPE NAME \| TYPE/NAME) KEY_1=VAL_1 ... KEY_N=VAL_N [--overwrite] [--all] [--resource-version=version] [flags] Add or update the labels of one or more resources.
logs kubectl logs POD [-c CONTAINER] [--follow] [flags] Print the logs for a container in a pod.
patch kubectl patch (-f FILENAME \| TYPE NAME \| TYPE/NAME) --patch PATCH [flags] Update one or more fields of a resource by using the strategic merge patch process.
port-forward kubectl port-forward POD [LOCAL_PORT:]REMOTE_PORT [...[LOCAL_PORT_N:]REMOTE_PORT_N] [flags] Forward one or more local ports to a pod.
proxy kubectl proxy [--port=PORT] [--www=static-dir] [--www-prefix=prefix] [--api-prefix=prefix] [flags] Run a proxy to the Kubernetes API server.
replace kubectl replace -f FILENAME Replace a resource from a file or stdin.
rolling-update kubectl rolling-update OLD_CONTROLLER_NAME ([NEW_CONTROLLER_NAME] --image=NEW_CONTAINER_IMAGE \| -f NEW_CONTROLLER_SPEC) [flags] Perform a rolling update by gradually replacing the specified replication controller and its pods.
run kubectl run NAME --image=image [--env="key=value"] [--port=port] [--replicas=replicas] [--dry-run=bool] [--overrides=inline-json] [flags] Run a specified image on the cluster.
scale kubectl scale (-f FILENAME \| TYPE NAME \| TYPE/NAME) --replicas=COUNT [--resource-version=version] [--current-replicas=count] [flags] Update the size of the specified replication controller.
stop kubectl stop Deprecated: Instead, see kubectl delete.
version kubectl version [--client] [flags] Display the Kubernetes version running on the client and server.

Remember: For more about command operations, see the kubectl reference documentation.

Resource types

The following table includes a list of all the supported resource types and their abbreviated aliases.

(This output can be retrieved from kubectl api-resources, and is accurate as of Kubernetes 1.13.3.)

Resource Name Short Names API Group Namespaced Resource Kind
componentstatuses cs false ComponentStatus
configmaps cm true ConfigMap
endpoints ep true Endpoints
limitranges limits true LimitRange
namespaces ns false Namespace
nodes no false Node
persistentvolumeclaims pvc true PersistentVolumeClaim
persistentvolumes pv false PersistentVolume
pods po true Pod
podtemplates true PodTemplate
replicationcontrollers rc true ReplicationController
resourcequotas quota true ResourceQuota
secrets true Secret
serviceaccounts sa true ServiceAccount
services svc true Service
mutatingwebhookconfigurations admissionregistration.k8s.io false MutatingWebhookConfiguration
validatingwebhookconfigurations admissionregistration.k8s.io false ValidatingWebhookConfiguration
customresourcedefinitions crd, crds apiextensions.k8s.io false CustomResourceDefinition
apiservices apiregistration.k8s.io false APIService
controllerrevisions apps true ControllerRevision
daemonsets ds apps true DaemonSet
deployments deploy apps true Deployment
replicasets rs apps true ReplicaSet
statefulsets sts apps true StatefulSet
tokenreviews authentication.k8s.io false TokenReview
localsubjectaccessreviews authorization.k8s.io true LocalSubjectAccessReview
selfsubjectaccessreviews authorization.k8s.io false SelfSubjectAccessReview
selfsubjectrulesreviews authorization.k8s.io false SelfSubjectRulesReview
subjectaccessreviews authorization.k8s.io false SubjectAccessReview
horizontalpodautoscalers hpa autoscaling true HorizontalPodAutoscaler
cronjobs cj batch true CronJob
jobs batch true Job
certificatesigningrequests csr certificates.k8s.io false CertificateSigningRequest
leases coordination.k8s.io true Lease
events ev events.k8s.io true Event
ingresses ing extensions true Ingress
networkpolicies netpol networking.k8s.io true NetworkPolicy
poddisruptionbudgets pdb policy true PodDisruptionBudget
podsecuritypolicies psp policy false PodSecurityPolicy
clusterrolebindings rbac.authorization.k8s.io false ClusterRoleBinding
clusterroles rbac.authorization.k8s.io false ClusterRole
rolebindings rbac.authorization.k8s.io true RoleBinding
roles rbac.authorization.k8s.io true Role
priorityclasses pc scheduling.k8s.io false PriorityClass
storageclasses sc storage.k8s.io false StorageClass
volumeattachments storage.k8s.io false VolumeAttachment

Output options

Use the following sections for information about how you can format or sort the output of certain commands. For details about which commands support the various output options, see the kubectl reference documentation.

Formatting output

The default output format for all kubectl commands is the human readable plain-text format. To output details to your terminal window in a specific format, you can add either the -o or --output flags to a supported kubectl command.

Syntax

kubectl [command] [TYPE] [NAME] -o <output_format>

Depending on the kubectl operation, the following output formats are supported:

Output format Description
-o custom-columns=<spec> Print a table using a comma separated list of custom columns.
-o custom-columns-file=<filename> Print a table using the custom columns template in the <filename> file.
-o json Output a JSON formatted API object.
-o jsonpath=<template> Print the fields defined in a jsonpath expression.
-o jsonpath-file=<filename> Print the fields defined by the jsonpath expression in the <filename> file.
-o name Print only the resource name and nothing else.
-o wide Output in the plain-text format with any additional information. For pods, the node name is included.
-o yaml Output a YAML formatted API object.
Example

In this example, the following command outputs the details for a single pod as a YAML formatted object:

kubectl get pod web-pod-13je7 -o yaml

Remember: See the kubectl reference documentation for details about which output format is supported by each command.

Custom columns

To define custom columns and output only the details that you want into a table, you can use the custom-columns option. You can choose to define the custom columns inline or use a template file: -o custom-columns=<spec> or -o custom-columns-file=<filename>.

Examples

Inline:

kubectl get pods <pod-name> -o custom-columns=NAME:.metadata.name,RSRC:.metadata.resourceVersion

Template file:

kubectl get pods <pod-name> -o custom-columns-file=template.txt

where the template.txt file contains:

NAME          RSRC
metadata.name metadata.resourceVersion

The result of running either command is:

NAME           RSRC
submit-queue   610995

Server-side columns

kubectl supports receiving specific column information from the server about objects. This means that for any given resource, the server will return columns and rows relevant to that resource, for the client to print. This allows for consistent human-readable output across clients used against the same cluster, by having the server encapsulate the details of printing.

This feature is enabled by default in kubectl 1.11 and higher. To disable it, add the --server-print=false flag to the kubectl get command.

Examples

To print information about the status of a pod, use a command like the following:

kubectl get pods <pod-name> --server-print=false

Output looks like this:

NAME       READY     STATUS              RESTARTS   AGE
pod-name   1/1       Running             0          1m

Sorting list objects

To output objects to a sorted list in your terminal window, you can add the --sort-by flag to a supported kubectl command. Sort your objects by specifying any numeric or string field with the --sort-by flag. To specify a field, use a jsonpath expression.

Syntax

kubectl [command] [TYPE] [NAME] --sort-by=<jsonpath_exp>
Example

To print a list of pods sorted by name, you run:

kubectl get pods --sort-by=.metadata.name

Examples: Common operations

Use the following set of examples to help you familiarize yourself with running the commonly used kubectl operations:

kubectl apply - Apply or Update a resource from a file or stdin.

# Create a service using the definition in example-service.yaml.
kubectl apply -f example-service.yaml

# Create a replication controller using the definition in example-controller.yaml.
kubectl apply -f example-controller.yaml

# Create the objects that are defined in any .yaml, .yml, or .json file within the <directory> directory.
kubectl apply -f <directory>

kubectl get - List one or more resources.

# List all pods in plain-text output format.
kubectl get pods

# List all pods in plain-text output format and include additional information (such as node name).
kubectl get pods -o wide

# List the replication controller with the specified name in plain-text output format. Tip: You can shorten and replace the 'replicationcontroller' resource type with the alias 'rc'.
kubectl get replicationcontroller <rc-name>

# List all replication controllers and services together in plain-text output format.
kubectl get rc,services

# List all daemon sets, including uninitialized ones, in plain-text output format.
kubectl get ds --include-uninitialized

# List all pods running on node server01
kubectl get pods --field-selector=spec.nodeName=server01

kubectl describe - Display detailed state of one or more resources, including the uninitialized ones by default.

# Display the details of the node with name <node-name>.
kubectl describe nodes <node-name>

# Display the details of the pod with name <pod-name>.
kubectl describe pods/<pod-name>

# Display the details of all the pods that are managed by the replication controller named <rc-name>.
# Remember: Any pods that are created by the replication controller get prefixed with the name of the replication controller.
kubectl describe pods <rc-name>

# Describe all pods, not including uninitialized ones
kubectl describe pods --include-uninitialized=false
Note: The kubectl get command is usually used for retrieving one or more resources of the same resource type. It features a rich set of flags that allows you to customize the output format using the -o or --output flag, for example. You can specify the -w or --watch flag to start watching updates to a particular object. The kubectl describe command is more focused on describing the many related aspects of a specified resource. It may invoke several API calls to the API server to build a view for the user. For example, the kubectl describe node command retrieves not only the information about the node, but also a summary of the pods running on it, the events generated for the node etc.

kubectl delete - Delete resources either from a file, stdin, or specifying label selectors, names, resource selectors, or resources.

# Delete a pod using the type and name specified in the pod.yaml file.
kubectl delete -f pod.yaml

# Delete all the pods and services that have the label name=<label-name>.
kubectl delete pods,services -l name=<label-name>

# Delete all the pods and services that have the label name=<label-name>, including uninitialized ones.
kubectl delete pods,services -l name=<label-name> --include-uninitialized

# Delete all pods, including uninitialized ones.
kubectl delete pods --all

kubectl exec - Execute a command against a container in a pod.

# Get output from running 'date' from pod <pod-name>. By default, output is from the first container.
kubectl exec <pod-name> date

# Get output from running 'date' in container <container-name> of pod <pod-name>.
kubectl exec <pod-name> -c <container-name> date

# Get an interactive TTY and run /bin/bash from pod <pod-name>. By default, output is from the first container.
kubectl exec -ti <pod-name> /bin/bash

kubectl logs - Print the logs for a container in a pod.

# Return a snapshot of the logs from pod <pod-name>.
kubectl logs <pod-name>

# Start streaming the logs from pod <pod-name>. This is similar to the 'tail -f' Linux command.
kubectl logs -f <pod-name>

Examples: Creating and using plugins

Use the following set of examples to help you familiarize yourself with writing and using kubectl plugins:

# create a simple plugin in any language and name the resulting executable file
# so that it begins with the prefix "kubectl-"
cat ./kubectl-hello
#!/bin/bash

# this plugin prints the words "hello world"
echo "hello world"

# with our plugin written, let's make it executable
sudo chmod +x ./kubectl-hello

# and move it to a location in our PATH
sudo mv ./kubectl-hello /usr/local/bin

# we have now created and "installed" a kubectl plugin.
# we can begin using our plugin by invoking it from kubectl as if it were a regular command
kubectl hello
hello world

# we can "uninstall" a plugin, by simply removing it from our PATH
sudo rm /usr/local/bin/kubectl-hello

In order to view all of the plugins that are available to kubectl, we can use the kubectl plugin list subcommand:

kubectl plugin list
The following kubectl-compatible plugins are available:

/usr/local/bin/kubectl-hello
/usr/local/bin/kubectl-foo
/usr/local/bin/kubectl-bar

# this command can also warn us about plugins that are
# not executable, or that are overshadowed by other
# plugins, for example
sudo chmod -x /usr/local/bin/kubectl-foo
kubectl plugin list

The following kubectl-compatible plugins are available:

/usr/local/bin/kubectl-hello
/usr/local/bin/kubectl-foo
  - warning: /usr/local/bin/kubectl-foo identified as a plugin, but it is not executable
/usr/local/bin/kubectl-bar

error: one plugin warning was found

We can think of plugins as a means to build more complex functionality on top of the existing kubectl commands:

cat ./kubectl-whoami
#!/bin/bash

# this plugin makes use of the `kubectl config` command in order to output
# information about the current user, based on the currently selected context
kubectl config view --template='{{ range .contexts }}{{ if eq .name "'$(kubectl config current-context)'" }}Current user: {{ .context.user }}{{ end }}{{ end }}'

Running the above plugin gives us an output containing the user for the currently selected context in our KUBECONFIG file:

# make the file executable
sudo chmod +x ./kubectl-whoami

# and move it into our PATH
sudo mv ./kubectl-whoami /usr/local/bin

kubectl whoami
Current user: plugins-user

To find out more about plugins, take a look at the example cli plugin.

What's next

Start using the kubectl commands.

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