2nd/10_Wiki/Topics/Coding/DevOps_Kubernetes_Basics.md

id, title, category, status, source_trust_level, verification_status, created_at, updated_at, tags, tech_stack, applied_in, aliases

id	title	category	status	source_trust_level	verification_status	created_at	updated_at	tags	tech_stack	applied_in	aliases
devops-kubernetes-basics	Kubernetes — Deployment / Service / Ingress	Coding	draft	B	conceptual	2026-05-09	2026-05-09	devops kubernetes k8s vibe-coding	language applicable_to YAML / kubectl DevOps		Deployment Service Ingress ConfigMap Secret HPA probes

Kubernetes Basics

Container orchestrator. Pod = 컨테이너 그룹, Deployment = pod replica 관리, Service = 안정 endpoint, Ingress = 외부 노출. Probes / resources / HPA 가 production hygiene.

📖 핵심 개념

• Namespace: 논리 분리.
• Pod: 1+ 컨테이너 단위, 같은 IP.
• ReplicaSet: pod 수 유지. (Deployment 가 사용)
• Deployment: rolling update.
• Service: stable IP / DNS, load balance.
• Ingress: HTTP path / host routing.

💻 코드 패턴

Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: api
  namespace: prod
spec:
  replicas: 3
  selector: { matchLabels: { app: api } }
  strategy:
    type: RollingUpdate
    rollingUpdate: { maxUnavailable: 0, maxSurge: 1 }
  template:
    metadata: { labels: { app: api } }
    spec:
      containers:
      - name: api
        image: ghcr.io/myco/api:1.2.3
        ports: [{ containerPort: 8080 }]
        env:
        - { name: NODE_ENV, value: production }
        - { name: DB_URL, valueFrom: { secretKeyRef: { name: db, key: url } } }
        resources:
          requests: { cpu: 100m, memory: 256Mi }
          limits:   { cpu: 500m, memory: 512Mi }
        readinessProbe:
          httpGet: { path: /healthz, port: 8080 }
          initialDelaySeconds: 5
          periodSeconds: 5
        livenessProbe:
          httpGet: { path: /livez, port: 8080 }
          initialDelaySeconds: 30
          periodSeconds: 10
        startupProbe:
          httpGet: { path: /healthz, port: 8080 }
          failureThreshold: 30
          periodSeconds: 2

Service

apiVersion: v1
kind: Service
metadata: { name: api, namespace: prod }
spec:
  type: ClusterIP
  selector: { app: api }
  ports: [{ port: 80, targetPort: 8080 }]

Ingress

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: api
  namespace: prod
  annotations:
    cert-manager.io/cluster-issuer: letsencrypt
spec:
  ingressClassName: nginx
  tls:
  - hosts: [api.myco.com]
    secretName: api-tls
  rules:
  - host: api.myco.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend: { service: { name: api, port: { number: 80 } } }

ConfigMap & Secret

apiVersion: v1
kind: ConfigMap
metadata: { name: app-config }
data:
  LOG_LEVEL: info
  FEATURE_X: "true"
---
apiVersion: v1
kind: Secret
metadata: { name: db }
type: Opaque
stringData:
  url: postgres://app:pw@db:5432/app

HPA (autoscale)

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata: { name: api }
spec:
  scaleTargetRef: { apiVersion: apps/v1, kind: Deployment, name: api }
  minReplicas: 2
  maxReplicas: 20
  metrics:
  - type: Resource
    resource: { name: cpu, target: { type: Utilization, averageUtilization: 70 } }

PDB (graceful disruption)

apiVersion: policy/v1
kind: PodDisruptionBudget
metadata: { name: api }
spec:
  minAvailable: 2
  selector: { matchLabels: { app: api } }

kubectl 자주 쓰는

kubectl get pods -n prod
kubectl logs -f deployment/api -n prod
kubectl describe pod <pod> -n prod
kubectl exec -it <pod> -n prod -- sh
kubectl rollout restart deployment/api -n prod
kubectl rollout undo deployment/api -n prod
kubectl top pods -n prod
kubectl port-forward svc/api 8080:80 -n prod

Helm chart 구조

charts/api/
  Chart.yaml
  values.yaml          # 기본값
  values-prod.yaml     # 환경별 override
  templates/
    deployment.yaml
    service.yaml
    ingress.yaml

🤔 의사결정 기준

상황	도구
단순 배포	raw YAML + kustomize
Reusable / 환경 다양	Helm chart
다중 환경 GitOps	Argo CD / Flux
복잡한 cron	Job / CronJob
Stateful (DB)	StatefulSet (또는 DB 매니지드)
Sidecars (proxy, log)	initContainer / sidecar

❌ 안티패턴

• Liveness만, Readiness 없음: warmup 안 끝났는데 트래픽.
• Resources 없음: 한 pod 가 노드 장악 / OOM.
• Limit = Request: throttling 심해짐. limit 좀 여유.
• Latest tag: 재현 불가. semver tag.
• Secret YAML 에 평문: SOPS / Sealed Secrets / External Secrets.
• Replicas 1 + PDB minAvailable 1: 노드 drain 못 함.
• maxUnavailable 1 + replicas 2: 50% 다운. 0/1 권장.
• HPA 없음 prod: 트래픽 spike 죽음.

🤖 LLM 활용 힌트

• Probes 3종 + resources + HPA + PDB 항상.
• Helm + Argo CD GitOps.
• ConfigMap 비밀X, Secret 평문X (SOPS).

🔗 관련 문서

• DevOps_Terraform_Patterns
• Backend_Cron_Patterns