Clase 07 — YAML en Kubernetes

Estructura básica de un manifiesto K8s

Todos los recursos de Kubernetes comparten estos campos:

apiVersion: v1                # Versión de la API
kind: Pod                     # Tipo de recurso
metadata:                     # Metadatos
  name: mi-pod
  namespace: default
  labels:
    app: mi-app
spec:                         # Especificación (varía por tipo)
  # ...

Pod

La unidad mínima en Kubernetes.

apiVersion: v1
kind: Pod
metadata:
  name: mi-pod
  labels:
    app: mi-app
    env: development
spec:
  containers:
    - name: app
      image: nginx:1.25-alpine
      ports:
        - containerPort: 80
      resources:
        requests:
          cpu: "100m"
          memory: "128Mi"
        limits:
          cpu: "250m"
          memory: "256Mi"

Deployment

Gestiona réplicas y actualizaciones de Pods.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: mi-api
  labels:
    app: mi-api
spec:
  replicas: 3
  selector:
    matchLabels:
      app: mi-api
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 0
  template:
    metadata:
      labels:
        app: mi-api
        version: "2.0"
    spec:
      containers:
        - name: api
          image: mi-registry/mi-api:2.0
          ports:
            - containerPort: 8080
          env:
            - name: APP_ENV
              value: "production"
            - name: DB_HOST
              valueFrom:
                configMapKeyRef:
                  name: db-config
                  key: host
            - name: DB_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: db-secret
                  key: password
          resources:
            requests:
              cpu: "250m"
              memory: "256Mi"
            limits:
              cpu: "500m"
              memory: "512Mi"
          livenessProbe:
            httpGet:
              path: /health
              port: 8080
            initialDelaySeconds: 15
            periodSeconds: 20
          readinessProbe:
            httpGet:
              path: /ready
              port: 8080
            initialDelaySeconds: 5
            periodSeconds: 10

Service

Expone los Pods como un servicio de red.

# ClusterIP (interno)
apiVersion: v1
kind: Service
metadata:
  name: mi-api-svc
spec:
  type: ClusterIP
  selector:
    app: mi-api
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080

---

# NodePort (acceso externo por puerto del nodo)
apiVersion: v1
kind: Service
metadata:
  name: mi-api-nodeport
spec:
  type: NodePort
  selector:
    app: mi-api
  ports:
    - port: 80
      targetPort: 8080
      nodePort: 30080

---

# LoadBalancer (cloud provider)
apiVersion: v1
kind: Service
metadata:
  name: mi-api-lb
spec:
  type: LoadBalancer
  selector:
    app: mi-api
  ports:
    - port: 80
      targetPort: 8080

ConfigMap

Almacena configuración no sensible.

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  APP_ENV: "production"
  LOG_LEVEL: "info"
  DB_HOST: "postgres-svc"
  DB_PORT: "5432"

  app.conf: |
    [server]
    host = 0.0.0.0
    port = 8080
    workers = 4

    [database]
    pool_size = 10
    timeout = 30

  nginx.conf: |
    server {
        listen 80;
        location / {
            proxy_pass http://mi-api-svc:80;
        }
    }

Usar ConfigMap en un Pod

apiVersion: v1
kind: Pod
metadata:
  name: mi-app
spec:
  containers:
    - name: app
      image: mi-app:latest
      envFrom:
        - configMapRef:
            name: app-config
      env:
        - name: DATABASE_HOST
          valueFrom:
            configMapKeyRef:
              name: app-config
              key: DB_HOST
      volumeMounts:
        - name: config-volume
          mountPath: /etc/app
  volumes:
    - name: config-volume
      configMap:
        name: app-config
        items:
          - key: app.conf
            path: app.conf
          - key: nginx.conf
            path: nginx.conf

Secret

Almacena datos sensibles (codificados en base64).

apiVersion: v1
kind: Secret
metadata:
  name: db-secret
type: Opaque
data:
  # echo -n "valor" | base64
  username: YWRtaW4=           # admin
  password: cDRzc3cwcmQ=       # p4ssw0rd

---
# stringData: texto plano, se codifica automáticamente
apiVersion: v1
kind: Secret
metadata:
  name: db-secret-v2
type: Opaque
stringData:
  username: admin
  password: p4ssw0rd

Ingress

Gestiona acceso HTTP/HTTPS externo.

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: mi-ingress
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target: /
    cert-manager.io/cluster-issuer: letsencrypt-prod
spec:
  ingressClassName: nginx
  tls:
    - hosts:
        - api.ejemplo.com
      secretName: api-tls
  rules:
    - host: api.ejemplo.com
      http:
        paths:
          - path: /api
            pathType: Prefix
            backend:
              service:
                name: mi-api-svc
                port:
                  number: 80
          - path: /
            pathType: Prefix
            backend:
              service:
                name: frontend-svc
                port:
                  number: 80

Múltiples documentos en un archivo

Usá --- para separar recursos en un mismo archivo.

apiVersion: v1
kind: Namespace
metadata:
  name: pokemon-app

---

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
  namespace: pokemon-app
data:
  APP_ENV: production
  API_PORT: "8080"

---

apiVersion: apps/v1
kind: Deployment
metadata:
  name: pokemon-api
  namespace: pokemon-app
spec:
  replicas: 2
  selector:
    matchLabels:
      app: pokemon-api
  template:
    metadata:
      labels:
        app: pokemon-api
    spec:
      containers:
        - name: api
          image: pokemon-api:latest
          ports:
            - containerPort: 8080
          envFrom:
            - configMapRef:
                name: app-config

---

apiVersion: v1
kind: Service
metadata:
  name: pokemon-api-svc
  namespace: pokemon-app
spec:
  selector:
    app: pokemon-api
  ports:
    - port: 80
      targetPort: 8080
  type: ClusterIP

Comandos útiles

kubectl apply -f deployment.yaml                    # Aplicar manifiesto
kubectl apply -f k8s/                               # Aplicar todo un directorio
kubectl apply -f deployment.yaml --dry-run=client   # Validar sin aplicar
kubectl get deployment mi-api -o yaml               # Ver YAML de un recurso
kubectl create deployment mi-app --image=nginx --dry-run=client -o yaml > deployment.yaml

Ejercicios

1. Creá un manifiesto completo con: Namespace, ConfigMap, Secret, Deployment y Service
2. Configurá un Deployment con probes (liveness y readiness) y límites de recursos
3. Creá un Ingress que enrute /api a un backend y / a un frontend