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Kubernetes Cheatsheet - kubectl

Components

Name Description
kube-apiserver validates and configures data for the api objects which include pods, services, replicationcontrollers, and others
etcd distributed k/v store
kube-scheduler schedule pods to run on selected nodes
kube-controller-manager daemon that embeds the core control loops shipped with kubernetes

Components and Services running on Worker Nodes:

Name Description
kubelet node-agent that runs on each node
kube-proxy connection forwarding
container runtime container runtimes supported by kubernets: (docker, rkt, runc, etc)

kubectl

Nodes

Show nodes in the cluster:

kubectl get nodes

Show nodes with extra info:

kubectl get nodes -o wide

Show nodes in yaml format:

kubectl get nodes -o yaml

Describe nodes:

kubectl describe nodes

Describe a specific node:

kubectl describe node/node-1

Show nodes in yaml format

kubectl get nodes -o yaml

Show node labels

kubectl get node --show-labels

Show nodes with specific label

kubectl get node --selector=[label_name]

Show value from a key

kubectl get nodes -o jsonpath='{.items[*].status.addresses[?(@.type=="External IP")].address}'

Get node resource information

kubectl top node [node_name]

Pods

  • The single smallest interactable unit in Kubernetes.
  • a Pod can be comprimised of multiple containers that will form a unit deployed on a single node together
  • a Pod receives one IP which is shared between containers

Show pods:

kubectl get pods

Show pods from all namespaces:

kubectl get pods --all-namespaces

Show pods in yaml format:

kubectl get pods --output yaml

Show system pods

kubectl get pods --namespace kube-system

Show pods in yaml format

kubectl get pods --output yaml

Show pods per specific node:

kubectl get pods --field-selector spec.nodeName=node-1 --all-namespaces -o wide

Dont truncate output

kubectl get pods -o wide

Show pod info

kubectl get pod svclb-traefik --namespace kube-system

Show pod info from app selector

kubectl get pods --selector app=svclb-traefik --namespace kube-system

Show pod info from multiple label selectors:

kubectl get pods -n kube-system -l 'app in (app-blue, app-green)'

To show only the pod name from the previous query:

kubectl get pods --selector app=svclb-traefik --namespace kube-system --output name 
# or
kubectl get pods --selector app=svclb-traefik --namespace kube-system -o jsonpath="{.items[0].metadata.name}"

Show all pods info from all ns

kubectl describe pods --all-namespaces

Show pods with labels

kubectl get pods --show-labels

Dump pod info in yaml

kubectl get pod svclb-traefik --namespace kube-system -o yaml --export

Export pod info to file

kubectl get pod svclb-traefik --namespace kube-system -o yaml --export > exported.yml

Show pods, sort by node

kubectl get pods -o wide --sort-by="{.spec.nodeName}"

Show pods, sort by restarts

kubectl get pods --sort-by="{.status.containerStatuses[:1].restartCount}"

Show pods on a node

kubectl get pods --all-namespaces -o wide --field-selector spec.nodeName="ip-10-10-4-20.eu-west-1.compute.internal"

Show pods from a deployment

kubectl get pods --output wide --selector app.kubernetes.io/name=my-app

Run a pod without a deployment (Restart policy with Never wont create a deployment)

kubectl run pod1 --image=alpine --restart=Never -- ping localhost

Run a pod without a deployment (Using generator flag)

kubectl run pod2 --generator=run-pod/v1 --image=alpine -- ping localhost

Run a debug pod:

kubectl run --generator=run-pod/v1 -it --rm load-generator --image=busybox /bin/sh

To see the deployment name of which the pod is part of:

# list the pods for the given namespace
kubectl get pods -n default

# view the pod and output the metadata that shows the replicaset
kubectl get pods/example-application-5dd6d8465b-dngfx -n default -o jsonpath='{.metadata.ownerReferences[*].name}'
example-application-5dd6d8465b

# view the replicaset and output the deployment name
kubectl get replicaset/example-application-5dd6d8465b -n default -o jsonpath='{.metadata.ownerReferences[*].name}'
example-application

Deployments

List deployments

kubectl get deployment

List deployments from all namespaces

kubectl get deployments --all-namespaces

Show deployment info

kubectl get deployment/myapp -o yaml

Run a Nginx Deployment with 2 Replicas

kubectl run nginx-app --image=nginx --replicas=2 --port=80

Rolling update "www" containers of "hostname" deployment, updating the image

kubectl set image deployment/hostname www=image:v3

Check the history of deployments including the revision

kubectl rollout history deployment/hostname

Rollback to the previous deployment

kubectl rollout undo deployment/hostname

Rollback to a specific revision

kubectl rollout undo deployment/hostname --to-revision=2

Watch rolling update status of "hostname" deployment until completion

kubectl rollout status -w deployment/hostname

View the deployment of a daemonset:

kubectl rollout status ds/promtail

Rolling restart of the "hostname" deployment

kubectl rollout restart deployment/hostname

Persistent Volumes

Logs

Tail logs from a pod:

kubectl logs -f drone-agent-557ddc7bb4-crjns

Tail logs from a container (when two or more containers runs in a pod):

kubectl logs -f drone-agent-557ddc7bb4-crjns -c docker-in-docker

Show pods and dont truncate the output:

kubectl get pods -o wide

Show pods with their labels:

kubectl get pods --show-labels

Show pods from a specific deployment:

kubectl get pods --output wide --selector app.kubernetes.io/name=my-test-app

Show pods on specific node:

kubectl get pods -o wide --field-selector spec.nodeName="ip-10-0-1-20.eu-west-1.compute.internal"

Show pods, sort output by node:

kubectl get pods -o wide --sort-by="{.spec.nodeName}"

Show pods, sort output by restarts:

kubectl get pods --sort-by="{.status.containerStatuses[:1].restartCount}"

Events

View kube-system events:

kubectl get events -n kube-system

View kube-system events, sorted by date:

kubectl get events -n kube-system --sort-by='.metadata.creationTimestamp'

Secrets

Create two files with the username and password:

echo -n 'admin' > ./username.txt
echo -n '1f2d1e2e67df' > ./password.txt

Create the secret:

kubectl create secret generic db-user-pass --from-file=admin-user=./username.txt --from-file=password=./password.txt
# or from literals
kubectl create secret generic db-user-pass --from-literal=admin-user=admin --from-literal=password='1f2d1e2e67df'

To view secrets:

kubectl get secrets

To view a specific secret:

kubectl get secret/db-user-pass -o yaml

To view them in json format:

kubectl get secret/db-user-pass -o jsonpath='{.data}'

As secrets are encoded with base64, we can decode and output the value:

kubectl get secret/db-user-pass -o jsonpath='{.data.admin-user}' | base64 -d

Or using template with index for our key:

kubectl get secret/db-user-pass --template='{{index .data "admin-user"}}' | base64 --decode

We can also redirect the output to pbcopy to copy it into your keyboard if you are using mac:

kubectl get secret/db-user-pass --template='{{index .data "admin-user"}}' | base64 --decode | pbcopy

To create multiple k/v in your secret from a file:

cat secrets.env

USERNAME=ruan
PASSWORD=foobar

Then generate the secret yaml:

kubectl -n default create secret generic app-secrets --from-env-file=secrets.env --type=Opaque --dry-run=client --output yaml > secrets.yaml

More resources:

CP

Copy a remote file from a container in a pod to local filesystem:

kubectl cp monitoring/prometheus-operator-grafana-x-x:/tmp/dump/grafana-backup.tar.gz ~/backups/grafana-backup.tar.gz -c grafana

Generate Manifests

Deployments:

kubectl create deployment nginx --namespace default --replicas 2 --image registry.gitlab.com/ruanbekker/containers:nginx --port 80 --dry-run=client -o yaml > deployment.yaml

Services:

kubectl expose deployment nginx --port 80 --target-port 80 --dry-run=client -o yaml > service.yaml

API Resources

To view all api resources, such as ingress, configmap, servicemonitor and any other CRDs:

kubectl api-resources

To view all the resources in a given namespace:

for obj in $(kubectl api-resources --verbs=list --namespaced -o name); do kubectl get $obj -n my-namespace --ignore-not-found --show-kind ; done

Troubleshooting

Pods

Let's look at a pod:

$ kubectl get pods -o wide
pistack-blog-7cddc5b979-grbv4              0/1     ContainerCreating   0          4m47s   <none>        rpi-03   <none>           <none>

We can see it's been in a ContainerCreating state for some time, we can have a look at the logs:

$ kubectl logs -f pod/pistack-blog-7cddc5b979-grbv4
Error from server (BadRequest): container "ghost" in pod "pistack-blog-7cddc5b979-grbv4" is waiting to start: ContainerCreating

Let's describe the pod to see whats currently happening:

$ kubectl describe pod/pistack-blog-7cddc5b979-grbv4
Name:         pistack-blog-7cddc5b979-grbv4
Namespace:    default
...
Events:
  Type    Reason     Age    From               Message
  ----    ------     ----   ----               -------
  Normal  Scheduled  8m21s  default-scheduler  Successfully assigned default/pistack-blog-7cddc5b979-grbv4 to rpi-03
  Normal  Pulling    8m20s  kubelet            Pulling image "alexellis2/ghost-on-docker:armv6"

We can see that the it's currently pulling the image from the registry, let's try again after a minute or so:

$ kubectl describe pod/pistack-blog-7cddc5b979-grbv4
Name:         pistack-blog-7cddc5b979-grbv4
Namespace:    default
...
Events:
  Type    Reason     Age    From               Message
  ----    ------     ----   ----               -------
  Normal  Scheduled  8m21s  default-scheduler  Successfully assigned default/pistack-blog-7cddc5b979-grbv4 to rpi-03
  Normal  Pulling    8m20s  kubelet            Pulling image "alexellis2/ghost-on-docker:armv6"
  Normal  Pulled     10s    kubelet            Successfully pulled image "alexellis2/ghost-on-docker:armv6"
  Normal  Created    6s     kubelet            Created container ghost
  Normal  Started    4s     kubelet            Started container ghost

We can also look at our nodes utilization, should we thought it was resource related:

$ kubectl top nodes
NAME     CPU(cores)   CPU%   MEMORY(bytes)   MEMORY%
rpi-01   163m         4%     303Mi           32%
rpi-02   229m         5%     318Mi           34%
rpi-03   276m         6%     330Mi           35%
rpi-05   1107m        27%    2222Mi          57%
rpi-06   298m         7%     467Mi           12%
rpi-07   238m         5%     416Mi           10%

Namespace not deleting

If you see the status of your namespace is Terminating, it could be because of a resource is prevented from deletion, you can look under the namespace using:

for obj in $(kubectl api-resources --verbs=list --namespaced -o name); do kubectl get $obj -n my-namespace --ignore-not-found --show-kind ; done

Ingress not deleting

If your ingress don't want to delete you can remove the finalizers source

kubectl patch ingress my-ingress -n my-namespace -p '{"metadata":{"finalizers":[]}}' --type=merge

Taints

To configure a node to not accept any more workloads but keep the existing pods running, you can set a taint to the node:

kubectl taint nodes ip-10-20-8-134.eu-west-1.compute.internal scheduling=enabled:NoSchedule

To remove the taint:

kubectl taint nodes ip-10-20-8-134.eu-west-1.compute.internal scheduling=enabled:NoSchedule-

Snippets

Pods

Example pod snippet:

# https://kubernetes.io/docs/concepts/workloads/pods/
apiVersion: v1
kind: Pod
metadata:
  name: "myapp"
  namespace: default
  labels:
    app: "myapp"
spec:
  containers:
  - name: myapp
    image: "debian-slim:latest"
    resources:
      limits:
        cpu: 200m
        memory: 500Mi
      requests:
        cpu: 100m
        memory: 200Mi
    env:
    - name: DB_HOST
      valueFrom:
        configMapKeyRef:
          name: myapp
          key: DB_HOST
    ports:
    - containerPort: 80
      name:  http
    volumeMounts:
    - name: localtime
      mountPath: /etc/localtime
  volumes:
    - name: localtime
      hostPath:
        path: /usr/share/zoneinfo/Asia/Tehran
  restartPolicy: Always

Deployment

Example deployment snippet:

# https://kubernetes.io/docs/concepts/workloads/controllers/deployment/
apiVersion: apps/v1
kind: Deployment
metadata:
  name:  myjob
  namespace: default
  labels:
    app: myjob
spec:
  selector:
    matchLabels:
      app: myjob
  replicas: 1
  strategy:
    rollingUpdate:
      maxSurge: 25%
      maxUnavailable: 25%
    type: RollingUpdate
  template:
    metadata:
      labels:
        app: myjob
    spec:
      # initContainers:
        # Init containers are exactly like regular containers, except:
          # - Init containers always run to completion.
          # - Each init container must complete successfully before the next one starts.
      containers:
      - name:  myjob
        image:  myjob:latest
        imagePullPolicy: IfNotPresent
        resources:
          requests:
            cpu: 100m
            memory: 100Mi
          limits:
            cpu: 100m
            memory: 100Mi
        livenessProbe:
          tcpSocket:
            port: 80
          initialDelaySeconds: 5
          timeoutSeconds: 5
          successThreshold: 1
          failureThreshold: 3
          periodSeconds: 10
        readinessProbe:
          httpGet:
            path: /_status/healthz
            port: 80
          initialDelaySeconds: 5
          timeoutSeconds: 2
          successThreshold: 1
          failureThreshold: 3
          periodSeconds: 10
        env:
        - name: DB_HOST
          valueFrom:
            configMapKeyRef:
              name: myjob
              key: DB_HOST
        ports:
        - containerPort:  80
          name:  myjob
        volumeMounts:
        - name: localtime
          mountPath: /etc/localtime
      volumes:
        - name: localtime
          hostPath:
            path: /usr/share/zoneinfo/Asia/Tehran
      restartPolicy: Always

Secret

Example secret snippet:

# https://kubernetes.io/docs/concepts/configuration/secret/
apiVersion: v1
kind: Secret
metadata:
  name: mysecret
  namespace: default
type: Opaque
data:
  password: cGFzc3dvcmQ=
  # echo -n 'password' | base64

Useful Aliases

alias k=kubectl
alias ktx=kubectx
alias kns=kubens
alias krun="kubectl run debug-pod --rm -it --restart='Never' --image ruanbekker/containers:curl -- sh

Useful Tools

  • kubectx : lets you switch between contexts (clusters) on kubectl faster.
  • kubens : lets you switch between Kubernetes namespaces (and configure them for kubectl) easily.
  • stern : lets you to tail multiple pods on Kubernetes and multiple containers within the pod.

External List of Tools

Resources:

Kubectl Output Formatting:

Kubectl Comprehensive Guide:

Kubernetes Cheatsheet:

CI/CD with Kubernets: