a.core_concepts.md

Core Concepts (13%)

kubernetes.io > Documentation > Reference > kubectl CLI > kubectl Cheat Sheet

kubernetes.io > Documentation > Tasks > Monitoring, Logging, and Debugging > Get a Shell to a Running Container

kubernetes.io > Documentation > Tasks > Access Applications in a Cluster > Configure Access to Multiple Clusters

kubernetes.io > Documentation > Tasks > Access Applications in a Cluster > Accessing Clusters using API

kubernetes.io > Documentation > Tasks > Access Applications in a Cluster > Use Port Forwarding to Access Applications in a Cluster

Create a namespace called 'mynamespace' and a pod with image nginx called nginx on this namespace

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kubectl create namespace mynamespace
kubectl run nginx --image=nginx --restart=Never -n mynamespace

Create the pod that was just described using YAML

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Easily generate YAML with:

kubectl run nginx --image=nginx --restart=Never --dry-run=client -n mynamespace -o yaml > pod.yaml

cat pod.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
  namespace: mynamespace
spec:
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

kubectl create -f pod.yaml

Alternatively, you can run in one line

kubectl run nginx --image=nginx --restart=Never --dry-run=client -o yaml | kubectl create -n mynamespace -f -

Create a busybox pod (using kubectl command) that runs the command "env". Run it and see the output

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kubectl run busybox --image=busybox --command --restart=Never -it -- env # -it will help in seeing the output
# or, just run it without -it
kubectl run busybox --image=busybox --command --restart=Never -- env
# and then, check its logs
kubectl logs busybox

Create a busybox pod (using YAML) that runs the command "env". Run it and see the output

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# create a  YAML template with this command
kubectl run busybox --image=busybox --restart=Never --dry-run=client -o yaml --command -- env > envpod.yaml
# see it
cat envpod.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: busybox
  name: busybox
spec:
  containers:
  - command:
    - env
    image: busybox
    name: busybox
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

# apply it and then see the logs
kubectl apply -f envpod.yaml
kubectl logs busybox

Get the YAML for a new namespace called 'myns' without creating it

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kubectl create namespace myns -o yaml --dry-run=client

Get the YAML for a new ResourceQuota called 'myrq' with hard limits of 1 CPU, 1G memory and 2 pods without creating it

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kubectl create quota myrq --hard=cpu=1,memory=1G,pods=2 --dry-run=client -o yaml

Get pods on all namespaces

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kubectl get po --all-namespaces

Alternatively

kubectl get po -A

Create a pod with image nginx called nginx and expose traffic on port 80

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kubectl run nginx --image=nginx --restart=Never --port=80

Change pod's image to nginx:1.7.1. Observe that the container will be restarted as soon as the image gets pulled

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Note: The RESTARTS column should contain 0 initially (ideally - it could be any number)

# kubectl set image POD/POD_NAME CONTAINER_NAME=IMAGE_NAME:TAG
kubectl set image pod/nginx nginx=nginx:1.7.1
kubectl describe po nginx # you will see an event 'Container will be killed and recreated'
kubectl get po nginx -w # watch it

Note: some time after changing the image, you should see that the value in the RESTARTS column has been increased by 1, because the container has been restarted, as stated in the events shown at the bottom of the kubectl describe pod command:

Events:
  Type    Reason     Age                  From               Message
  ----    ------     ----                 ----               -------
[...]
  Normal  Killing    100s                 kubelet, node3     Container pod1 definition changed, will be restarted
  Normal  Pulling    100s                 kubelet, node3     Pulling image "nginx:1.7.1"
  Normal  Pulled     41s                  kubelet, node3     Successfully pulled image "nginx:1.7.1"
  Normal  Created    36s (x2 over 9m43s)  kubelet, node3     Created container pod1
  Normal  Started    36s (x2 over 9m43s)  kubelet, node3     Started container pod1

Note: you can check pod's image by running

kubectl get po nginx -o jsonpath='{.spec.containers[].image}{"\n"}'

Get nginx pod's ip created in previous step, use a temp busybox image to wget its '/'

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kubectl get po -o wide # get the IP, will be something like '10.1.1.131'
# create a temp busybox pod
kubectl run busybox --image=busybox --rm -it --restart=Never -- wget -O- 10.1.1.131:80

Alternatively you can also try a more advanced option:

# Get IP of the nginx pod
NGINX_IP=$(kubectl get pod nginx -o jsonpath='{.status.podIP}')
# create a temp busybox pod
kubectl run busybox --image=busybox --env="NGINX_IP=$NGINX_IP" --rm -it --restart=Never -- sh -c 'wget -O- $NGINX_IP:80'

Or just in one line:

kubectl run busybox --image=busybox --rm -it --restart=Never -- wget -O- $(kubectl get pod nginx -o jsonpath='{.status.podIP}:{.spec.containers[0].ports[0].containerPort}')

Get pod's YAML

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kubectl get po nginx -o yaml
# or
kubectl get po nginx -oyaml
# or
kubectl get po nginx --output yaml
# or
kubectl get po nginx --output=yaml

Get information about the pod, including details about potential issues (e.g. pod hasn't started)

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kubectl describe po nginx

Get pod logs

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kubectl logs nginx

If pod crashed and restarted, get logs about the previous instance

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kubectl logs nginx -p

Execute a simple shell on the nginx pod

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kubectl exec -it nginx -- /bin/sh

Create a busybox pod that echoes 'hello world' and then exits

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kubectl run busybox --image=busybox -it --restart=Never -- echo 'hello world'
# or
kubectl run busybox --image=busybox -it --restart=Never -- /bin/sh -c 'echo hello world'

Do the same, but have the pod deleted automatically when it's completed

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kubectl run busybox --image=busybox -it --rm --restart=Never -- /bin/sh -c 'echo hello world'
kubectl get po # nowhere to be found :)

Create an nginx pod and set an env value as 'var1=val1'. Check the env value existence within the pod

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kubectl run nginx --image=nginx --restart=Never --env=var1=val1
# then
kubectl exec -it nginx -- env
# or
kubectl exec -it nginx -- sh -c 'echo $var1'
# or
kubectl describe po nginx | grep val1
# or
kubectl run nginx --restart=Never --image=nginx --env=var1=val1 -it --rm -- env