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kubernetes.md

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Kubernetes

Overview

graph LR

api --- scheduler
api --- control
api --- etcd

api -.- kublet1
api -.- kublet2

%% k8s admin
user["User (You)"]
user --- kubectl
kubectl -.- api

subgraph server0["Server (Control Plane)"]

  api["API Server"]
  etcd[Etcd]
  scheduler["Scheduler"]
  control["Controller Manager"]
end

subgraph server1["Server (Worker Node)"]
  kublet1[Kublet]
  kublet1 --- containerd1

  containerd1[containerd]
  containerd1 --- pod1_1
  containerd1 --- pod1_2

  pod1_1[pod]
  pod1_2[pod]
 
end

subgraph server2["Server (Worker Node)"]
  kublet2[Kublet]
  kublet2 --- containerd2

  containerd2[containerd]
  containerd2 --- pod2_1
  containerd2 --- pod2_2

  pod2_1[pod]
  pod2_2[pod]
end
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High-level view of Kubernetes cluster components.

  • API Server: Interface for users and other K8s services
  • Etcd: Persistent storage for ressource configuration
  • Scheduler: Tracks worker nodes and decides where to run pods
  • Kublet: Runs on every worker node to manage pods
graph LR

  %% resources
  internet
  
  %% relations
  internet --- ingress

  subgraph cluster["Kubernetes Cluster"]

    subgraph namespace

      %% resources
      ingress
      cert-manager
      service
      secret

      %% relations
      ingress --- service
      ingress -.- cert-manager
      service --- pod1
      service --- pod2
      service --- pod3
      pod1 -.- secret
      pod2 -.- secret
      pod3 -.- secret
      
      subgraph deployment
      
        %% resources
        pod1
        pod2
        pod3
      
      end
    
    end

  end
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High-level view of Kubernetes Resources.

Cluster Access

  • Default cluster: $HOME/.kube/config
  • Use othe cluster: KUBECONFIG=~/.kube/server.yaml kubectl ..
  • Forward Kubernetes API: ssh -NL 6443:127.0.01:6443 server01.example.com

Debugging

Exec

# jump into existing container
kubectl exec --stdin --tty <pod-name> -- /bin/bash

Describe

kubectl describe pod <name>

Port Forward

kubectl port-forward --namespace kube-system <pod.name> 9000:9000

Run

# run a new container for debugging purpose
kubectl run toolbox --namespace apps --rm -i --tty --image debian -- bash

Resource types

Namespace

  • Mechanism for isolating groups of resources
  • Default namespcaes, cannot be deleted:
    • kube-sytem: For Kubernetes components
    • kube-public: For public resources
    • default: FOr user resources
# create namespace
kubectl create namespace myapp

# list all namespaces
kubectl get namespace

# delete a namespace
kubectl delete namespace myapp

# set default namespace
kubectl config set-context --current --namespace=myapp

# get pods in namespace
kubectl --namespace myapp get pods

Pods

  • Pods are the smallest deployable units of computing that you can create and manage in Kubernetes
  • A Pod is a group of one or more containers, with shared storage and network resources
# run pod
kubectl run awesome-app --image=nginx:latest

# list pods
kubectl get pods

# delete pod
kubectl delete pod awesome-app

Deployment

  • A deployment provides declarative updates for Pods
  • Covers update process, health and more
# create deployment
kubectl apply -f deployment.yaml

# list deployments
kubectl get deployments

# delete deployment
kubectl delete deployment example-web
deployment.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: example-web
  name: example-web
spec:
  replicas: 1
  selector:
    matchLabels:
      app: example-web
  template:
    metadata:
      labels:
        app: example-web
    spec:
      containers:
      - image: nginx:latest
        name: example-web
        resources:
          requests:
            cpu: 10m
            memory: 16Mi
          limits:
            cpu: 20m
            memory: 32Mi

Secrets

  • Object that contains a small amount of sensitive data such as a password, a token, or a key
# create secret
kubectl create secret generic <name> --from-file=<name1>=/tmp/test1 --from-file=<name2>=/tmp/regcred

# list secrets
kubectl get secrets

# get secret
kubectl get secret regcred --output=yaml
Private Registry

Example --from-file-file:

{"auths":{"registry.example.com":{"username":"<token-username>","password":"<token>","email":"<token-username>@example.com"}}}

Service

  • An ressource to expose an application running on a set of Pods as a network service
# get services
kubectl get services

Node

  • Kubernetes Nodes
# list all nodes
kubectl get node -o wide

Tools

  • k9s - provides a terminal UI to interact with Kubernetes
brew install k9s
k9s --namespace myapp
  • k3d - lightweight wrapper to run k3s in docker
brew install k3d
k3d cluster create mycluster --api-port 6550 -p "80:80@loadbalancer"
  • Helm - The package manager for Kubernetes
brew install helm
  • Lens - The Kubernetes IDE
brew install --cask lens