# 수동으로 각 서버에 접속해서...
ssh server1
docker run -d -p 80:80 shopping-app

ssh server2
docker run -d -p 80:80 shopping-app

# 로드밸런서 설정도 수동으로...
# 모니터링도 직접...
# 장애 발생하면 새벽에 일어나서 복구... 😴

# Kubernetes로는 이렇게 간단히!
apiVersion: apps/v1
kind: HorizontalPodAutoscaler
metadata:
  name: shopping-app-hpa
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: shopping-app
  minReplicas: 3
  maxReplicas: 100
  targetCPUUtilizationPercentage: 50

# Docker Compose - 개발 환경
docker-compose up -d
# 단일 호스트, 수동 관리, 간단한 설정

# Kubernetes - 프로덕션 환경
kubectl apply -f deployment.yaml
# 멀티 호스트, 자동 관리, 강력한 기능

# minikube 설치 (로컬 Kubernetes 클러스터)
# macOS
brew install minikube

# Windows (관리자 권한 PowerShell)
choco install minikube

# Linux
curl -LO https://storage.googleapis.com/minikube/releases/latest/minikube-linux-amd64
sudo install minikube-linux-amd64 /usr/local/bin/minikube

# 클러스터 시작
minikube start

# 상태 확인
kubectl cluster-info

# 1. Deployment 생성 (애플리케이션 실행)
kubectl create deployment first-app --image=nginx:latest

# 2. 배포 상태 확인
kubectl get deployments
# NAME        READY   UP-TO-DATE   AVAILABLE   AGE
# first-app   1/1     1            1           30s

# 3. Pod 확인 (실제 실행 중인 컨테이너)
kubectl get pods
# NAME                         READY   STATUS    RESTARTS   AGE
# first-app-6b7b9f5b9d-x7n4m   1/1     Running   0          45s

# 4. Service 생성 (외부 노출)
kubectl expose deployment first-app --port=80 --type=LoadBalancer

# 5. Service 확인
kubectl get services
# NAME         TYPE           CLUSTER-IP      EXTERNAL-IP   PORT(S)        AGE
# first-app    LoadBalancer   10.96.232.123   <pending>     80:31234/TCP   10s

# minikube는 실제 LoadBalancer가 없으므로 터널링 사용
minikube service first-app

# 또는 포트 포워딩
kubectl port-forward service/first-app 8080:80
# 이제 http://localhost:8080 으로 접속 가능!

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3  # 3개의 복제본 실행
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.21
        ports:
        - containerPort: 80
        resources:
          requests:
            memory: "64Mi"
            cpu: "250m"
          limits:
            memory: "128Mi"
            cpu: "500m"

apiVersion: v1
kind: Service
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx
  type: LoadBalancer
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80

# 배포
kubectl apply -f deployment.yaml
kubectl apply -f service.yaml

# 또는 한 번에
kubectl apply -f .

# 상태 모니터링
kubectl get all
kubectl describe deployment nginx-deployment
kubectl logs -l app=nginx

# 스케일링
kubectl scale deployment nginx-deployment --replicas=5

# 업데이트 (이미지 변경)
kubectl set image deployment/nginx-deployment nginx=nginx:1.22

# 롤백
kubectl rollout undo deployment/nginx-deployment

# 기본 조회
kubectl get pods
kubectl get deployments
kubectl get services
kubectl get nodes

# 자세한 정보
kubectl get pods -o wide
kubectl get pods -o yaml

# 레이블로 필터링
kubectl get pods -l app=nginx

# 모든 네임스페이스
kubectl get pods --all-namespaces

# describe: 이벤트와 상세 정보
kubectl describe pod <pod-name>
kubectl describe deployment <deployment-name>

# logs: 컨테이너 로그
kubectl logs <pod-name>
kubectl logs <pod-name> -f  # 실시간 로그
kubectl logs <pod-name> --previous  # 이전 컨테이너 로그

# 생성
kubectl create -f <file.yaml>
kubectl apply -f <file.yaml>  # 생성 또는 업데이트

# 수정
kubectl edit deployment <name>
kubectl patch deployment <name> -p '{"spec":{"replicas":5}}'

# 삭제
kubectl delete -f <file.yaml>
kubectl delete deployment <name>
kubectl delete pod <name> --force --grace-period=0  # 강제 삭제

# Pod 내부 접속
kubectl exec -it <pod-name> -- /bin/bash

# 포트 포워딩
kubectl port-forward pod/<pod-name> 8080:80

# 리소스 사용량
kubectl top nodes
kubectl top pods

# 이벤트 확인
kubectl get events --sort-by=.metadata.creationTimestamp

// app.js
const express = require('express');
const app = express();
const port = 3000;

app.get('/', (req, res) => {
  res.json({
    message: 'Hello Kubernetes!',
    hostname: process.env.HOSTNAME,
    version: '1.0.0'
  });
});

app.get('/health', (req, res) => {
  res.status(200).send('OK');
});

app.listen(port, () => {
  console.log(`App listening at http://localhost:${port}`);
});

# Dockerfile
FROM node:16-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY . .
EXPOSE 3000
CMD ["node", "app.js"]

# k8s-app.yaml
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: node-app
  labels:
    app: node-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: node-app
  template:
    metadata:
      labels:
        app: node-app
    spec:
      containers:
      - name: node-app
        image: your-dockerhub-username/node-app:1.0.0
        ports:
        - containerPort: 3000
        env:
        - name: NODE_ENV
          value: "production"
        resources:
          requests:
            memory: "128Mi"
            cpu: "100m"
          limits:
            memory: "256Mi"
            cpu: "200m"
        livenessProbe:
          httpGet:
            path: /health
            port: 3000
          initialDelaySeconds: 30
          periodSeconds: 10
        readinessProbe:
          httpGet:
            path: /health
            port: 3000
          initialDelaySeconds: 5
          periodSeconds: 5
---
apiVersion: v1
kind: Service
metadata:
  name: node-app-service
spec:
  selector:
    app: node-app
  type: LoadBalancer
  ports:
    - protocol: TCP
      port: 80
      targetPort: 3000

# Docker 이미지 빌드 및 푸시
docker build -t your-dockerhub-username/node-app:1.0.0 .
docker push your-dockerhub-username/node-app:1.0.0

# Kubernetes 배포
kubectl apply -f k8s-app.yaml

# 배포 확인
kubectl get all -l app=node-app

# 로그 확인
kubectl logs -l app=node-app

# 서비스 테스트
kubectl port-forward service/node-app-service 8080:80
curl http://localhost:8080

# 1. Pod 상태 확인
kubectl get pods
kubectl describe pod <pod-name>

# 2. 일반적인 문제들
# - ImagePullBackOff: 이미지를 가져올 수 없음
#   → 이미지 이름/태그 확인, 레지스트리 인증 확인
# - CrashLoopBackOff: 컨테이너가 계속 재시작
#   → 로그 확인: kubectl logs <pod-name>
# - Pending: 스케줄링 되지 않음
#   → 리소스 부족, 노드 셀렉터 확인

# 1. Service와 Endpoints 확인
kubectl get svc
kubectl get endpoints

# 2. 레이블 셀렉터 매칭 확인
kubectl get pods --show-labels
kubectl describe svc <service-name>

# 3. 네트워크 정책 확인
kubectl get networkpolicies

resources:
  requests:
    memory: "128Mi"
    cpu: "100m"
  limits:
    memory: "256Mi"
    cpu: "200m"

livenessProbe:
  httpGet:
    path: /health
    port: 8080
  initialDelaySeconds: 30
  periodSeconds: 10

readinessProbe:
  httpGet:
    path: /ready
    port: 8080
  initialDelaySeconds: 5
  periodSeconds: 5

labels:
  app: myapp
  version: v1.0.0
  environment: production
  team: backend