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568 lines
19 KiB
Markdown
568 lines
19 KiB
Markdown
# Kubectl <!-- omit in toc -->
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Command line tool for communicating with a Kubernetes cluster's control plane using the Kubernetes API.
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Resource types are case **in**sensitive and can be specified in their singular, plural or abbreviated form for convenience:
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```sh
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# The two commands below are equivalent.
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kubectl get deployment,replicasets,pods -A
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kubectl get deploy,rs,po -A
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```
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Use `kubectl api-resources` to check out the available resources and their abbreviations.
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Multiple resources types can be specified together, but only one resource name is accepted at a time.
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Resource names are case sensitive and will filter the requested resources; use the `-l`, `--selector` option to get around filtering:
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```sh
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kubectl get deployments,replicasets -A
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kubectl get pod etcd-minikube -n kube-system
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kubectl get pods -l app=nginx,tier=frontend
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```
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### Table of contents
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- [TL;DR](#tldr)
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- [Configuration](#configuration)
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- [Configure access to multiple clusters](#configure-access-to-multiple-clusters)
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- [Create resources](#create-resources)
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- [Output formatting](#output-formatting)
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- [Verbosity and debugging](#verbosity-and-debugging)
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- [Further readings](#further-readings)
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- [Sources](#sources)
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## TL;DR
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```sh
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# Enable shell completion.
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source <(kubectl completion bash)
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echo "[[ $commands[kubectl] ]] && source <(kubectl completion zsh)" >> ~/.zshrc
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# Shot the merged configuration.
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kubectl config view
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# Get specific values from the configuration.
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kubectl config view -o jsonpath='{.users[].name}'
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kubectl config view -o jsonpath='{.users[*].name}'
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kubectl config view -o jsonpath='{.users[?(@.name == "e2e")].user.password}'
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# Set configuration values.
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kubectl config set-context --current --namespace=keda
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kubectl config set-context gce --user=cluster-admin --namespace=foo
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kubectl config set-credentials \
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kubeuser/foo.kubernetes.com --username=kubeuser --password=kubepassword
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# Delete configuration values.
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kubectl config unset users.foo
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# Use multiple config files at once.
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# This will temporarily merge them in one big configuration file.
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KUBECONFIG="path/to/config1:path/to/configN"
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# List contexts.
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kubectl config get-contexts
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kubectl config current-context
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# Set context as the default one.
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kubectl config use-context docker-desktop
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kubectl config use-context gce
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# Display addresses of the master and services.
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kubectl cluster-info
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# Dump the complete current cluster state.
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kubectl cluster-info dump
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kubectl cluster-info dump --output-directory=/path/to/cluster-state
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# List supported resources types along with their short name, API group, Kind,
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# and whether they are namespaced.
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kubectl api-resources
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kubectl api-resources --namespaced=true
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kubectl api-resources -o name
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kubectl api-resources -o wide
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kubectl api-resources --verbs=list,get
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# Show the documentation about resources or their fields.
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kubectl explain pods
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kubectl explain pods.spec.containers
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# List and filter resources.
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kubectl get pods
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kubectl get pod/coredns-845757d86-47np2 -n kube-system
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kubectl get namespaces,pods --show-labels
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kubectl get services -A -o wide
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kubectl get rs --sort-by=.metadata.name
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kubectl get pv --sort-by=.spec.capacity.storage --no-headers
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kubectl get po --sort-by='.status.containerStatuses[0].restartCount'
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kubectl get events --sort-by .metadata.creationTimestamp
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kubectl get pods --field-selector=status.phase=Running
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kubectl get node -l='!node-role.kubernetes.io/master'
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kubectl get replicasets -l 'environment in (prod, qa)'
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kubectl get deploy --selector 'tier,tier notin (frontend)'
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# Extract information from resources' definition.
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kubectl get deployment nginx -o yaml
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kubectl get cm kube-root-ca.crt -o jsonpath='{.data.ca\.crt}'
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kubectl get po -o=jsonpath='{.items..metadata.name}'
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kubectl get po -l app=redis -o jsonpath='{.items[*].metadata.labels.version}'
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kubectl get nodes \
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-o jsonpath='{.items[*].status.addresses[?(@.type=="ExternalIP")].address}'
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# List all fields under '.metadata' regardless of their name.
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kubectl get pods -A -o=custom-columns='DATA:metadata.*'
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# List images being run in a cluster.
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kubectl get po -A -o=custom-columns='DATA:spec.containers[*].image'
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kubectl get po -A -o=custom-columns='DATA:spec.containers[?(@.image!="k8s.gcr.io/coredns:1.6.2")].image'
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# List all pods in status 'Shutdown'.
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kubectl get po -A \
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-o jsonpath='{.items[?(@.status.reason=="Shutdown")].metadata.name}'
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# List ready nodes.
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kubectl get nodes \
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-o jsonpath='{range .items[*]}{@.metadata.name}:{range @.status.conditions[*]}{@.type}={@.status};{end}{end}' \
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| grep "Ready=True"
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# List all secrets currently in use by a Pod.
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kubectl get pods -o json \
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| jq '.items[].spec.containers[].env[]?.valueFrom.secretKeyRef.name' \
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| grep -v null | sort | uniq
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# List the name of Pods belonging to a particular RC.
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SELECTOR=${$(kubectl get rc my-rc --output=json | jq -j '.spec.selector | to_entries | .[] | "\(.key)=\(.value),"')%?} kubectl get pods -l=$SELECTOR \
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-o=jsonpath='{.items..metadata.name}'
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# List the containerID of initContainers from all Pods.
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# Helpful when cleaning up stopped containers while avoiding the removal of
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# initContainers
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kubectl get pods --all-namespaces \
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-o jsonpath='{range .items[*].status.initContainerStatuses[*]}{.containerID}{"\n"}{end}' \
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| cut -d/ -f3
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# Produce a period-delimited tree of all keys returned for nodes.
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# Helpful when trying to locate a specific key within a complex nested JSON
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# structure.
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kubectl get nodes -o json | jq -c 'path(..)|[.[]|tostring]|join(".")'
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# Show detailed information about resources.
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kubectl describe node pi
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kubectl describe deploy,rs,po -l app=redis
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# Create resources from manifests.
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kubectl apply -f manifest.yaml
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kubectl apply -f path/to/m1.yaml -f ./m2.yaml
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kubectl apply -f dir/
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kubectl apply -f https://git.io/vPieo
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cat <<-EOF | kubectl apply -f -
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apiVersion: v1
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kind: Secret
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metadata:
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name: mysecret
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type: Opaque
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data:
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password: $(echo -n "s33msi4" | base64 -w0)
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username: $(echo -n "jane" | base64 -w0)
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EOF
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# Compare the current state of the cluster against the state it would be in if
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# a manifest was applied
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kubectl diff -f ./manifest.yaml
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# Start a Pod.
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kubectl run nginx --image nginx
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kubectl run busybox --rm -it --image=busybox -n keda -- sh
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# Start a Pod and write its specs into a file.
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kubectl run nginx --image=nginx --dry-run=client -o yaml > pod.yaml
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# Create a single instance deployment of 'nginx'.
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kubectl create deployment nginx --image=nginx
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# Start a Job using an existing Job as template
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kubectl create job backup-before-upgrade-13.6.2-to-13.9.2 \
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--from=cronjob.batch/backup -n gitlab
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# Wait for a pod to be 'ready'.
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kubectl wait --for 'condition=ready' --timeout 120s \
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pod -l 'app.kubernetes.io/component=controller'
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# Update the 'image' field of the 'www' containers from the 'frontend'
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# Deployment.
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# This starts a rolling update.
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kubectl set image deployment/frontend www=image:v2
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# Show the history of resources, including the revision.
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kubectl rollout history deployment/frontend
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# Rollback resources to the latest previous version.
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kubectl rollout undo deployment/frontend
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# Rollback resources to a specific revision.
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kubectl rollout undo deployment/frontend --to-revision=2
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# Follow the rolling update status of the 'frontend' Deployment until its
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# completion.
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kubectl rollout status -w deployment/frontend
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# Start a rolling restart of the 'frontend' Deployment.
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kubectl rollout restart deployment/frontend
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# Replace a Pod based on the JSON passed into stdin.
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cat pod.json | kubectl replace -f -
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# Force replacement, deletion and recreation (in this order) of resources.
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# This Will cause a service outage.
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kubectl replace --force -f ./pod.json
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# Create a service for a replicated 'nginx'.
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# Set it to serve on port 80 and connect to the containers on port 8000.
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kubectl expose rc nginx --port=80 --target-port=8000
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# Update a single-container Pod's image tag.
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kubectl get pod mypod -o yaml \
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| sed 's/\(image: myimage\):.*$/\1:v4/' \
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| kubectl replace -f -
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# Add Labels to resources.
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kubectl label pods nginx custom-name=awesome
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# Add Annotations.
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kubectl annotate pods alpine icon-url=http://goo.gl/XXBTWq
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# Autoscale resources.
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kubectl autoscale deployment foo --min=2 --max=10
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# Partially update resources.
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kubectl patch node k8s-node-1 -p '{"spec":{"unschedulable":true}}'
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# Update a container's image.
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# 'spec.containers[*].name' is required to specify the path of the merged key.
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kubectl patch pod valid-pod \
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-p '{"spec":{"containers": [{"name": "kubernetes-serve-hostname","image":"new image"}]}}'
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# Update a container's image using a JSONPatch with positional arrays.
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kubectl patch pod valid-pod --type='json' \
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-p='[{"op": "replace", "path": "/spec/containers/0/image", "value":"new image"}]'
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# Disable a Deployment's livenessProbe using a JSONPatch with positional arrays.
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kubectl patch deployment valid-deployment --type json \
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-p='[{"op": "remove", "path": "/spec/template/spec/containers/0/livenessProbe"}]'
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# Add a new element to a positional array.
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kubectl patch sa default --type='json' \
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-p='[{"op": "add", "path": "/secrets/1", "value": {"name": "whatever" } }]'
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# Edit the service named docker-registry.
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kubectl edit svc/docker-registry
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KUBE_EDITOR="nano" kubectl edit svc/docker-registry
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# Scale a replicaset named 'foo' to 3
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kubectl scale --replicas=3 rs/foo
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# Scale a resource specified in "foo.yaml" to 3 replicas.
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kubectl scale --replicas=3 -f foo.yaml
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# If the Deployment named 'mysql''s current size is 2, scale it to 3.
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kubectl scale --current-replicas=2 --replicas=3 deployment/mysql
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# Scale multiple ReplicationControllers at once.
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kubectl scale --replicas=5 rc/foo rc/bar rc/baz
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# Delete a Pod using the type and name specified in pod.json.
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kubectl delete -f ./pod.json
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# Delete Pods and Services named 'baz' and 'foo'.
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kubectl delete pod,service baz foo
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# Delete pods and services with Label name=myLabel.
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kubectl delete pods,services -l name=myLabel
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# Delete all pods and services in namespace my-ns.
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kubectl -n my-ns delete pod,svc --all
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# Delete all pods matching awk's pattern1 or pattern2.
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kubectl get pods --no-headers \
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| awk '/pattern1|pattern2/{print $1}' \
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| xargs -n1 kubectl delete pods
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# Delete non-default service accounts.
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kubectl get serviceaccounts \
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-o jsonpath="{.items[?(@.metadata.name!='default')].metadata.name}" \
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| xargs -n1 kubectl delete serviceaccounts
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# Attach to a running container.
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kubectl attach my-pod -i
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# Run command in existing Pods.
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kubectl exec my-pod -- ls /
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kubectl exec my-pod -c my-container -- ls /
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# Show metrics for a given Pod and its containers.
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kubectl top pod busybox --containers
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# Get logs from resources.
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kubectl logs redis-0
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kubectl logs -l name=myLabel
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kubectl logs my-pod -c my-container
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# Follow logs.
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kubectl logs -f my-pod
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kubectl logs -f my-pod -c my-container
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kubectl logs -f -l name=myLabel --all-containers
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# Get logs for a previous instantiation of a container.
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kubectl logs nginx --previous
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# Get the logs of the first Pod matching ID.
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kubectl logs $(kubectl get pods --no-headers | grep $ID | awk '{print $2}')
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# Verify user's permissions on the cluster.
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kubectl auth can-i create roles
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kubectl auth can-i list pods
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# Taint a Node.
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kubectl taint nodes node1 key1=value1:NoSchedule
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# Taint all nodes in a certain nodepool (Azure AKS).
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kubectl get no -l "agentpool=nodepool1" -o jsonpath='{.items[*].metadata.name}'
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| xargs -n1 -I{} -p kubectl taint nodes {} key1=value1:NoSchedule
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# Remove a taint.
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# Notice the '-' sign at the end.
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kubectl taint nodes node1 key1=value1:NoSchedule-
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# If a taint with that key and effect already exists, replace its value.
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kubectl taint nodes foo dedicated=special-user:NoSchedule
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# Mark Nodes as unschedulable.
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kubectl cordon my-node
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# Mark my-node as schedulable.
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kubectl uncordon my-node
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# Drain my-node in preparation for maintenance.
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kubectl drain my-node
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# Show metrics for a given node.
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kubectl top node my-node
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# Listen on port 5000 on the local machine and forward connections to port 6000
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# of my-pod
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kubectl port-forward my-pod 5000:6000
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```
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## Configuration
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The configuration files are loaded as follows:
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1. If the `--kubeconfig` flag is set, then only that file is loaded; the flag may only be set **once**, and no merging takes place:
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```sh
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kubectl config --kubeconfig config.local view
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```
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2. If the `$KUBECONFIG` environment variable is set, then it is used as a list of paths following the normal path delimiting rules for your system; the files are merged:
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```sh
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export KUBECONFIG="/tmp/config.local:.kube/config.prod"
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```
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When a value is modified, it is modified in the file that defines the stanza; when a value is created, it is created in the first existing file; if no file in the chain exist, then the last file in the list is created with the configuration.
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3. If none of the above happens, `~/.kube/config` is used, and no merging takes place.
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The configuration file can be edited, or acted upon from the command line:
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```sh
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# Show the merged configuration.
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kubectl config view
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KUBECONFIG="~/.kube/config:config.local" kubectl config view
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# Show specific values only.
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kubectl config view -o jsonpath='{.users[].name}'
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kubectl config view -o jsonpath='{.users[?(@.name == "e2e")].user.password}'
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# Add a new user that supports basic auth.
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kubectl config set-credentials kubeuser/foo.kubernetes.com \
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--username=kubeuser --password=kubepassword
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# Delete user 'foo'.
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kubectl config unset users.foo
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# List the available contexts.
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kubectl config get-contexts
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# Display the current default context name.
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kubectl config current-context
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# Set the default context.
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kubectl config use-context minikube
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# Permanently setup specific contexts.
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kubectl config set-context --current --namespace=ggckad-s2
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kubectl config set-context gce --user=cluster-admin --namespace=foo
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```
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### Configure access to multiple clusters
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See [configure access to multiple clusters] for details.
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## Create resources
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The preferred way to create resources is to define them inside `manifest`s and then apply those:
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```yaml
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---
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# file manifest.yaml
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---
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apiVersion: v1
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kind: Pod
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metadata:
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name: busybox-sleep
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spec:
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containers:
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- name: busybox
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image: busybox
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args:
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- sleep
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- "1000000"
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---
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apiVersion: v1
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kind: Pod
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metadata:
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name: busybox-sleep-less
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spec:
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containers:
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- name: busybox
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image: busybox
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args:
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- sleep
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- "1000"
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```
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```sh
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# Apply the manifest.
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kubectl apply -f manifest.yaml
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# Apply multiple manifests together.
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kubectl apply -f path/to/m1.yaml -f m2.yaml
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# Apply all manifests in a directory.
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kubectl apply -f ./dir
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# Apply a remote manifest.
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kubectl apply -f https://git.io/vPieo
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# Define a manifest using HEREDOC and apply it.
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cat <<EOF | kubectl apply -f -
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apiVersion: v1
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kind: Secret
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metadata:
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name: mysecret
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type: Opaque
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data:
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password: $(echo -n "s33msi4" | base64 -w0)
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username: $(echo -n "jane" | base64 -w0)
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EOF
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```
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When subsequentially (re-)applying manifests, one can compare the current state of the cluster against the state it would be in if the manifest was applied:
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```sh
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kubectl diff -f manifest.yaml
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```
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Resources can also be created using default values or specifying them on the command line:
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```sh
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# Start a Pod.
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kubectl run nginx --image nginx
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kubectl run busybox --rm -it --image=busybox -n keda -- sh
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# Start a Pod and write its specs into a file.
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kubectl run nginx --image=nginx --dry-run=client -o yaml > pod.yaml
|
|
|
|
# Create a single instance deployment of 'nginx'.
|
|
kubectl create deployment nginx --image=nginx
|
|
|
|
# Start a Job using an existing Job as template
|
|
kubectl create job backup-before-upgrade-13.6.2-to-13.9.2 \
|
|
--from=cronjob.batch/backup -n gitlab
|
|
```
|
|
|
|
## Output formatting
|
|
|
|
Add the `-o`, `--output` option to a command:
|
|
|
|
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, and for pods, the node name is included
|
|
`-o=yaml` | Output a YAML formatted API object
|
|
|
|
Examples using `-o=custom-columns`:
|
|
|
|
```sh
|
|
# Print all the container images running in the cluster.
|
|
kubectl get pods -A -o=custom-columns='DATA:spec.containers[*].image'
|
|
|
|
# As above, but exclude 'k8s.gcr.io/coredns:1.6.2' from the list.
|
|
kubectl get pods -A \
|
|
-o=custom-columns='DATA:spec.containers[?(@.image!="k8s.gcr.io/coredns:1.6.2")].image'
|
|
|
|
# Print all fields under 'metadata' regardless of their name
|
|
kubectl get pods -A -o=custom-columns='DATA:metadata.*'
|
|
```
|
|
|
|
## Verbosity and debugging
|
|
|
|
Verbosity is controlled through the `-v` flag, or `--v` followed by an integer representing the log level.
|
|
|
|
General Kubernetes logging conventions and the associated log levels are described in the following table:
|
|
|
|
Verbosity | Description
|
|
--------- | -----------
|
|
`--v=0` | Generally useful for this to always be visible to a cluster operator.
|
|
`--v=1` | A reasonable default log level if you don't want verbosity.
|
|
`--v=2` | Useful steady state information about the service and important log messages that may correlate to significant changes in the system. This is the recommended default log level for most systems.
|
|
`--v=3` | Extended information about changes.
|
|
`--v=4` | Debug level verbosity.
|
|
`--v=6` | Display requested resources.
|
|
`--v=7` | Display HTTP request headers.
|
|
`--v=8` | Display HTTP request contents.
|
|
`--v=9` | Display HTTP request contents without truncation of contents.
|
|
|
|
|
|
## Further readings
|
|
|
|
- [Assigning Pods to Nodes]
|
|
- [Taints and Tolerations]
|
|
- [Commands reference]
|
|
- [Configure access to multiple clusters]
|
|
|
|
## Sources
|
|
|
|
- [Cheatsheet]
|
|
- [Run a single-instance stateful application]
|
|
- [Run a replicated stateful application]
|
|
- [Accessing an application on Kubernetes in Docker]
|
|
|
|
<!-- docs -->
|
|
[assigning pods to nodes]: https://kubernetes.io/docs/concepts/scheduling-eviction/assign-pod-node/
|
|
[cheatsheet]: https://kubernetes.io/docs/reference/kubectl/cheatsheet
|
|
[commands reference]: https://kubernetes.io/docs/reference/generated/kubectl/kubectl-commands
|
|
[configure access to multiple clusters]: https://kubernetes.io/docs/tasks/access-application-cluster/configure-access-multiple-clusters/
|
|
[taints and tolerations]: https://kubernetes.io/docs/concepts/scheduling-eviction/taint-and-toleration/
|
|
|
|
<!-- other articles -->
|
|
[accessing an application on kubernetes in docker]: https://medium.com/@lizrice/accessing-an-application-on-kubernetes-in-docker-1054d46b64b1
|
|
[run a replicated stateful application]: https://kubernetes.io/docs/tasks/run-application/run-replicated-stateful-application/
|
|
[run a single-instance stateful application]: https://kubernetes.io/docs/tasks/run-application/run-single-instance-stateful-application/
|