devops-exercises/topics/kubernetes/CKA.md

CKA (Certified Kubernetes Administrator)

• CKA (Certified Kubernetes Administrator)
  • Setup
  • Pods
    • Troubleshooting Pods
  • Namespaces
  • Nodes
  • Services

Setup

• Set up Kubernetes cluster. Use on of the following

  1. Minikube for local free & simple cluster
  2. Managed Cluster (EKS, GKE, AKS)

• Set aliases

alias k=kubectl
alias kd=kubectl delete
alias kds=kubectl describe
alias ke=kubectl edit
alias kr=kubectl run
alias kg=kubectl get

Pods

Run a command to view all the pods in current namespace

Note: create an alias (alias k=kubectl) and get used to k get po

Run a pod called "nginx-test" using the "nginx" image

k run nginx-test --image=nginx

Assuming you have a Pod called "nginx-test", how to remove it?

k delete nginx-test

In what namespace the etcd pod is running? list the pods in that namespace

k get po -n kube-system

List pods from all namespaces

k get po --all-namespaces

Write a YAML of a Pod with two containers and use the YAML file to create the Pod (use whatever images you prefer)

cat > pod.yaml <<EOL
apiVersion: v1
kind: Pod
metadata:
  name: test
spec:
  containers:
  - image: alpine
    name: alpine
  - image: nginx-unprivileged
    name: nginx-unprivileged
EOL

k create -f pod.yaml

Create a YAML of a Pod without actually running the Pod with the kubectl command (use whatever image you prefer)

k run some-pod -o yaml --image nginx-unprivileged --dry-run=client > pod.yaml

How to test a manifest is valid?

with --dry-run flag which will not actually create it, but it will test it and you can find this way any syntax issues.

k create -f YAML_FILE --dry-run

How to check which image a certain Pod is using?

k describe po <POD_NAME> | grep -i image

How to check how many containers run in signle Pod?

k get po POD_NAME and see the number under "READY" column.

You can also run k describe po POD_NAME

Run a Pod called "remo" with the the latest redis image and the label 'year=2017'

k run remo --image=redis:latest -l year=2017

List pods and their labels

k get po --show-labels

Troubleshooting Pods

You try to run a Pod but see the status "CrashLoopBackOff". What does it means? How to identify the issue?

The container failed to run (due to different reasons) and Kubernetes tries to run the Pod again after some delay (= BackOff time).

Some reasons for it to fail:

• Misconfiguration - mispelling, non supported value, etc.
• Resource not available - nodes are down, PV not mounted, etc.

Some ways to debug:

1. kubectl describe pod POD_NAME
   1. Focus on State (which should be Waiting, CrashLoopBackOff) and Last State which should tell what happened before (as in why it failed)
2. Run kubectl logs mypod
   1. This should provide an accurate output of
   2. For specific container, you can add -c CONTAINER_NAME
3. If you still have no idea why it failed, try kubectl get events

What the error ImagePullBackOff means?

Most likely you didn't write correctly the name of the image you try to pull and run

You can confirm with kubectl describe po POD_NAME

How to check on which node a certain Pod is running?

k get po POD_NAME -o wide

Namespaces

List all the namespaces

k get ns

Create a namespace called 'alle'

k create ns alle

Nodes

Run a command to view all nodes of the cluster

kubectl get nodes

Note: create an alias (alias k=kubectl) and get used to k get no

Create a list of all nodes in JSON format and store it in a file called "some_nodes.json"

k get nodes -o json > some_nodes.json

Services

Create an internal service called "sevi" to expose the app 'web' on port 1991