Add CKA page

Author: abregman

README.md

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 :information_source:  This repo contains questions and exercises on various technical topics, sometimes related to DevOps and SRE
 
-:bar_chart:  There are currently **2471** exercises and questions
+:bar_chart:  There are currently **2477** exercises and questions
 
 :books:  To learn more about DevOps and SRE, check the resources in [devops-resources](https://github.com/bregman-arie/devops-resources) repository
 

topics/kubernetes/CKA.md

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+# CKA (Certified Kubernetes Administrator)
+
+- [CKA (Certified Kubernetes Administrator)](#cka-certified-kubernetes-administrator)
+  - [Setup](#setup)
+  - [Kubernetes Nodes](#kubernetes-nodes)
+  - [Pods](#pods)
+    - [Troubleshooting Pods](#troubleshooting-pods)
+  - [Namespaces](#namespaces)
+
+## 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
+```
+
+## Kubernetes Nodes
+
+<details>
+<summary>Run a command to view all nodes of the cluster</summary><br><b>
+
+`kubectl get nodes`
+
+Note: create an alias (`alias k=kubectl`) and get used to `k get no`
+</b></details>
+
+## Pods
+
+<details>
+<summary>Run a command to view all the pods in current namespace</summary><br><b>
+
+Note: create an alias (`alias k=kubectl`) and get used to `k get po`
+</b></details>
+
+<details>
+<summary>Run a pod called "nginx-test" using the "nginx" image</summary><br><b>
+
+`k run nginx-test --image=nginx`
+</b></details>
+
+<details>
+<summary>Assuming you have a Pod called "nginx-test", how to remove it?</summary><br><b>
+
+`k delete nginx-test`
+</b></details>
+
+<details>
+<summary>In what namespace the <code>etcd</code> pod is running? list the pods in that namespace</summary><br><b>
+
+`k get po -n kube-system`
+</b></details>
+
+<details>
+<summary>List pods from all namespaces</summary><br><b>
+
+`k get po --all-namespaces`
+</b></details>
+
+<details>
+<summary>Write a YAML of a Pod with two containers and use the YAML file to create the Pod (use whatever images you prefer)</summary><br><b>
+
+```
+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
+```
+</b></details>
+
+<details>
+<summary>Create a YAML of a Pod without actually running the Pod with the kubectl command (use whatever image you prefer)</summary><br><b>
+
+`k run some-pod -o yaml --image nginx-unprivileged --dry-run=client > pod.yaml`
+</b></details>
+
+<details>
+<summary>How to test a manifest is valid?</summary><br><b>
+
+with `--dry-run` flag which will not actually create it, but it will test it and you can find this way any syntax issues.
+
+`kubectl create -f YAML_FILE --dry-run`
+</b></details>
+
+### Troubleshooting Pods
+
+<details>
+<summary>You try to run a Pod but see the status "CrashLoopBackOff". What does it means? How to identify the issue?</summary><br><b>
+
+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`
+</b></details>
+
+<details>
+<summary>What the error <code>ImagePullBackOff</code> means?</summary><br><b>
+
+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`
+</b></details>
+
+## Namespaces
+
+<details>
+<summary>List all the namespaces</summary><br><b>
+
+`k get ns`
+</b></details>