a.core_concepts.md

Core Concepts (13%)

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 -n mynamespace --dry-run -o yaml > pod.yaml

cat pod.yaml

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

kubectl create -f pod.yaml -n mynamespace

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 -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

Get the YAML for a new ResourceQuota called 'myrq' without creating it

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kubectl create resourcequota myrq -o yaml --dry-run

Get pods on all namespaces

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kubectl get po --all-namespaces

Create a pod with image nginx called nginx and allow 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 pod will be killed and recreated as soon as the image gets pulled

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# 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

Get the pod's ip, 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 -- sh
# run wget on specified IP:Port
wget -O- 10.1.1.131:80
exit

Get this pod's YAML without cluster specific information

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kubectl get po nginx -o yaml --export

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

Connect to 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 describe po nginx | grep val1

# or

kubectl run nginx --restart=Never --image=nginx --env=var1=val1 -it --rm -- env