---
aliases:
language: English
created: 2025-09-24
summary: My preparation notes for the kubernetes CAD certificate by linux foundation
tags:
  - resource
---




- Suggested IDE: vscode
	- YAML extension by Red Hat, configure in the extension settings the YAML schema and set this in the settings.json: `"yaml.schemas": {

        "kubernetes": "*.yaml"

    }`
	- restart the IDE afterwards
- kubectl
	- has very good --help options even on subcommands! with example commands
	- `kubectl run nginx --image=nginx` will fetch the nginx image from docker hub and create a pod
	- `kubectl create deployment nginx --image=nginx` creates a deployment
	- `kubectl create -f pod-definition.yml` create from file (`kubectl apply -f file.yml` works too?)
	- `kubectl get pods`
	- `kubectl set image deployment/nginx busybox=buysbox nginx=nginx:1.9.1` (or pod/nginx ...)
		- maybe also try `kubectl edit ...`
		- or change the yaml file and do `kubectl apply -f redis.yaml`
	- `kubectl describe pod myapp-pod`
	- `kubectl run redis --image=redis123 --dry-run=client -o yaml > redis.yaml` create yaml specification file for a pod
	- `kubectl get replicaset` and `kubectl get replicacontroller`
	- `kubectl scale --replicas=6 -f replicaset-definition.yml` better than `kubectl scale --replicas=6 replicaset myapp-replicaset` because latter only modifies deployed definition and not source file
	- `kubectl apply -f replicaset-definition.yml`
	- `kubectl get all` (lists deployment, then replicaset, then pods)
- scaling: we create additional pods. a pod can contain multiple containers but one pod shall only contain what is necessary for one instance of the application. we do NOT create additional containers in the same pod
- deployment: recreate (all down, then all new up) vs rollingUpdate (default, scales down/up replicasets by one at a time). `kubectl rollout undo deployment/myapp-deployment` will roll back
- minikube: bundles master node programs and node programs on one machine. requires virtualization (via hypervisor KVM, VirtualBox... or docker but latter is not recommended)
- ctr: CLI for containerD, not very user friendly and mostly for debugging
	- It is advised to use nerdctl instead
- nerdctl: provides docker-like CLI for containerd, supports docker compose, supports newest features in containerD (encrypted container images, lazy pulling...)
- crictl: provides a CLI for CRI-compatible container runtimes, installed separately, used to inspect and debug container runtimes (not to create containers ideally), works across different runtimes
	- `crictl pods` shows pods
	- `crictl --runtime endpoint` enables you to specify a runtime endpoint (or use CONTAINER_RUNTIME_ENDPOINT env var)
	- other commands are similar to docker

Kubernetes definition file:
```yml
apiVersion: v1
kind: Pod
metadata:  //dictionary, can only have name and labels
	name: myapp-pod
	labels: // can have any sub-attributes
		app: myapp
spec:  //individual for all deployments
  containers:
    - name: nginx-container
      image: nginx
```

## Glossary
- CRI: Container Runtime Interface
	- Kubernetes originally only worked for Docker but then introduced the CRI to be more abstract and allow all sorts of container runtimes
- OCI: Open Container Initiative
	- imagespec: specification on how an image should be build
	- runtimespec: standards on how a container runtime shall be deployed