obsidian-vault/Default/Kubernetes CAD.md

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

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