65 lines
3.3 KiB
Markdown
65 lines
3.3 KiB
Markdown
---
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aliases:
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language: English
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created: 2025-09-24
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summary: My preparation notes for the kubernetes CAD certificate by linux foundation
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tags:
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- resource
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---
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- Suggested IDE: vscode
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- YAML extension by Red Hat, configure in the extension settings the YAML schema and set this in the settings.json: `"yaml.schemas": {
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"kubernetes": "*.yaml"
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}`
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- restart the IDE afterwards
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- kubectl
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- has very good --help options even on subcommands! with example commands
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- `kubectl run nginx --image=nginx` will fetch the nginx image from docker hub and create a pod
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- `kubectl create deployment nginx --image=nginx` creates a deployment
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- `kubectl create -f pod-definition.yml` create from file (`kubectl apply -f file.yml` works too?)
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- `kubectl get pods`
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- `kubectl set image deployment/nginx busybox=buysbox nginx=nginx:1.9.1` (or pod/nginx ...)
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- maybe also try `kubectl edit ...`
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- or change the yaml file and do `kubectl apply -f redis.yaml`
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- `kubectl describe pod myapp-pod`
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- `kubectl run redis --image=redis123 --dry-run=client -o yaml > redis.yaml` create yaml specification file for a pod
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- `kubectl get replicaset` and `kubectl get replicacontroller`
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- `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
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- `kubectl apply -f replicaset-definition.yml`
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- `kubectl get all` (lists deployment, then replicaset, then pods)
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- 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
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- 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
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- minikube: bundles master node programs and node programs on one machine. requires virtualization (via hypervisor KVM, VirtualBox... or docker but latter is not recommended)
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- ctr: CLI for containerD, not very user friendly and mostly for debugging
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- It is advised to use nerdctl instead
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- nerdctl: provides docker-like CLI for containerd, supports docker compose, supports newest features in containerD (encrypted container images, lazy pulling...)
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- 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
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- `crictl pods` shows pods
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- `crictl --runtime endpoint` enables you to specify a runtime endpoint (or use CONTAINER_RUNTIME_ENDPOINT env var)
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- other commands are similar to docker
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Kubernetes definition file:
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```yml
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apiVersion: v1
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kind: Pod
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metadata: //dictionary, can only have name and labels
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name: myapp-pod
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labels: // can have any sub-attributes
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app: myapp
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spec: //individual for all deployments
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containers:
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- name: nginx-container
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image: nginx
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```
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## Glossary
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- CRI: Container Runtime Interface
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- Kubernetes originally only worked for Docker but then introduced the CRI to be more abstract and allow all sorts of container runtimes
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- OCI: Open Container Initiative
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- imagespec: specification on how an image should be build
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- runtimespec: standards on how a container runtime shall be deployed |