YAML 在 Kubernetes 中如何使用？有哪些常见的 Kubernetes YAML 配置模式？ - 面试题

YAML 在 Kubernetes 中扮演着核心角色，是声明式配置的主要格式。理解 YAML 在 Kubernetes 中的应用对于容器编排和云原生开发至关重要。

Kubernetes YAML 的基本结构

标准的 Kubernetes 资源 YAML 结构

yaml
apiVersion: apps/v1           # API 版本
kind: Deployment              # 资源类型
metadata:                     # 元数据
  name: nginx-deployment
  namespace: default
  labels:
    app: nginx
spec:                         # 规格说明
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.21
        ports:
        - containerPort: 80

核心 YAML 字段详解

1. apiVersion

指定 Kubernetes API 的版本，不同的资源类型可能使用不同的 API 版本。

yaml
# 常见的 API 版本
apiVersion: v1                    # 核心资源（Pod, Service, ConfigMap）
apiVersion: apps/v1               # 应用资源（Deployment, StatefulSet, DaemonSet）
apiVersion: networking.k8s.io/v1  # 网络资源（Ingress, NetworkPolicy）
apiVersion: batch/v1              # 批处理资源（Job, CronJob）
apiVersion: rbac.authorization.k8s.io/v1  # RBAC 资源

2. kind

指定要创建的 Kubernetes 资源类型。

yaml
# 常见的资源类型
kind: Pod
kind: Service
kind: Deployment
kind: StatefulSet
kind: DaemonSet
kind: ConfigMap
kind: Secret
kind: Ingress
kind: PersistentVolume
kind: PersistentVolumeClaim

3. metadata

包含资源的元数据，如名称、命名空间、标签、注解等。

yaml
metadata:
  name: my-app                    # 资源名称（必填）
  namespace: production           # 命名空间（默认为 default）
  labels:                         # 标签（用于选择器和组织）
    app: my-app
    version: v1.0
    environment: production
  annotations:                    # 注解（用于存储元数据）
    description: "Main application"
    contact: "team@example.com"

4. spec

定义资源的期望状态，这是最复杂的部分，内容因资源类型而异。

常见 Kubernetes 资源的 YAML 示例

Pod

yaml
apiVersion: v1
kind: Pod
metadata:
  name: nginx-pod
  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"
    env:
    - name: ENVIRONMENT
      value: "production"
    volumeMounts:
    - name: config-volume
      mountPath: /etc/config
  volumes:
  - name: config-volume
    configMap:
      name: nginx-config

Deployment

yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-app
  labels:
    app: web-app
spec:
  replicas: 3
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 0
  selector:
    matchLabels:
      app: web-app
  template:
    metadata:
      labels:
        app: web-app
    spec:
      containers:
      - name: web-app
        image: myapp:1.0
        ports:
        - containerPort: 8080
        livenessProbe:
          httpGet:
            path: /health
            port: 8080
          initialDelaySeconds: 30
          periodSeconds: 10
        readinessProbe:
          httpGet:
            path: /ready
            port: 8080
          initialDelaySeconds: 5
          periodSeconds: 5

Service

yaml
apiVersion: v1
kind: Service
metadata:
  name: web-service
spec:
  type: ClusterIP              # ClusterIP, NodePort, LoadBalancer, ExternalName
  selector:
    app: web-app
  ports:
  - protocol: TCP
    port: 80                   # Service 端口
    targetPort: 8080           # 目标 Pod 端口
    name: http
  - protocol: TCP
    port: 443
    targetPort: 8443
    name: https

ConfigMap

yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  # 键值对形式
  database.url: "postgresql://db.example.com:5432/myapp"
  cache.ttl: "3600"
  
  # 文件形式
  nginx.conf: |
    server {
      listen 80;
      server_name localhost;
      
      location / {
        proxy_pass http://backend:8080;
      }
    }

Secret

yaml
apiVersion: v1
kind: Secret
metadata:
  name: app-secret
type: Opaque
data:
  # Base64 编码的值
  username: YWRtaW4=
  password: cGFzc3dvcmQ=
stringData:
  # 明文值（自动编码）
  api-key: "your-api-key-here"

高级 YAML 特性在 Kubernetes 中的应用

1. 多文档 YAML

使用 --- 分隔符在一个文件中定义多个资源。

yaml
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  config.yaml: |
    key: value
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-deployment
spec:
  replicas: 2
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - name: app
        image: myapp:latest

2. 使用 ConfigMap 和 Secret

yaml
apiVersion: v1
kind: Pod
metadata:
  name: config-demo
spec:
  containers:
  - name: app
    image: myapp:latest
    env:
    # 从 ConfigMap 读取环境变量
    - name: DATABASE_URL
      valueFrom:
        configMapKeyRef:
          name: app-config
          key: database.url
    # 从 Secret 读取环境变量
    - name: API_KEY
      valueFrom:
        secretKeyRef:
          name: app-secret
          key: api-key
    # 挂载 ConfigMap 作为文件
    volumeMounts:
    - name: config-volume
      mountPath: /etc/config
  volumes:
  - name: config-volume
    configMap:
      name: app-config

3. 资源限制和请求

yaml
apiVersion: v1
kind: Pod
metadata:
  name: resource-limits
spec:
  containers:
  - name: app
    image: myapp:latest
    resources:
      requests:
        memory: "256Mi"
        cpu: "500m"
      limits:
        memory: "512Mi"
        cpu: "1000m"

4. 健康检查

yaml
apiVersion: v1
kind: Pod
metadata:
  name: health-check
spec:
  containers:
  - name: app
    image: myapp:latest
    livenessProbe:
      httpGet:
        path: /health
        port: 8080
      initialDelaySeconds: 30
      periodSeconds: 10
      timeoutSeconds: 5
      failureThreshold: 3
    readinessProbe:
      httpGet:
        path: /ready
        port: 8080
      initialDelaySeconds: 5
      periodSeconds: 5
      timeoutSeconds: 3
      failureThreshold: 3

YAML 最佳实践

1. 使用命名空间组织资源

yaml
apiVersion: v1
kind: Namespace
metadata:
  name: production
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app
  namespace: production
spec:
  # ...

2. 使用标签和选择器

yaml
metadata:
  labels:
    app: myapp
    version: v1.0
    environment: production
    tier: backend
spec:
  selector:
    matchLabels:
      app: myapp
      environment: production

3. 使用注解存储元数据

yaml
metadata:
  annotations:
    description: "Main application deployment"
    contact: "team@example.com"
    git-commit: "abc123"
    deployment-date: "2024-01-01"

4. 使用资源限制

yaml
resources:
  requests:
    memory: "256Mi"
    cpu: "500m"
  limits:
    memory: "512Mi"
    cpu: "1000m"

常见错误和解决方案

1. 缩进错误

yaml
# ❌ 错误：缩进不一致
spec:
  containers:
  - name: app
    image: myapp:latest
    ports:
    - containerPort: 8080
    - containerPort: 8443  # 缩进不一致

# ✅ 正确：一致的缩进
spec:
  containers:
  - name: app
    image: myapp:latest
    ports:
    - containerPort: 8080
    - containerPort: 8443

2. 类型错误

yaml
# ❌ 错误：端口应该是数字
ports:
- containerPort: "8080"  # 字符串

# ✅ 正确：使用数字
ports:
- containerPort: 8080

3. 必填字段缺失

yaml
# ❌ 错误：缺少 selector
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app
spec:
  replicas: 3
  # 缺少 selector

# ✅ 正确：包含 selector
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp

工具和验证

kubectl 验证

bash
# 验证 YAML 语法
kubectl apply --dry-run=client -f deployment.yaml

# 验证并查看生成的资源
kubectl apply --dry-run=server -f deployment.yaml

# 查看差异
kubectl diff -f deployment.yaml

YAML Linter

bash
# 使用 yamllint
yamllint deployment.yaml

# 使用 kubeval
kubeval deployment.yaml

掌握 Kubernetes YAML 的使用对于云原生应用开发至关重要，它提供了声明式配置的强大能力。