Deployment: 滚动更新与发布策略

深入剖析 Kubernetes Deployment 的控制器模型, 滚动更新原理, 回滚机制以及蓝绿/金丝雀等高阶发布策略.

Deployment 是 Kubernetes 中最常用的控制器, 它建立在 ReplicaSet 之上, 提供了强大的版本管理和声明式更新能力.

1. 控制器模型

1.1 层级关系

对象	职责
Deployment	版本管理, 更新策略
ReplicaSet	维护指定数量的 Pod 副本
Pod	实际运行的工作负载

1.2 控制循环

2. Deployment 配置

2.1 完整示例

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web
  labels:
    app: web
spec:
  replicas: 3
  revisionHistoryLimit: 10
  progressDeadlineSeconds: 600
  selector:
    matchLabels:
      app: web
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 25%
      maxUnavailable: 25%
  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
      - name: web
        image: nginx:1.21
        ports:
        - containerPort: 80
        readinessProbe:
          httpGet:
            path: /healthz
            port: 80
          initialDelaySeconds: 5
          periodSeconds: 5
        resources:
          requests:
            cpu: 100m
            memory: 128Mi
          limits:
            cpu: 500m
            memory: 256Mi

2.2 关键字段

字段	描述
`revisionHistoryLimit`	保留的历史 RS 数量
`progressDeadlineSeconds`	更新超时时间
`minReadySeconds`	Pod 就绪后等待时间
`paused`	暂停更新

3. 更新策略

3.1 RollingUpdate (滚动更新)

strategy:
  type: RollingUpdate
  rollingUpdate:
    maxSurge: 25%          # 可超出期望值的 Pod 数
    maxUnavailable: 25%    # 可不可用的 Pod 数

更新过程:

计算示例 (replicas=4):

maxSurge=25% → 最多 5 个 Pod (4 + 1)
maxUnavailable=25% → 最少 3 个可用 (4 - 1)

3.2 Recreate (重建)

strategy:
  type: Recreate

行为: 先删除所有旧 Pod, 再创建新 Pod

适用场景
不能同时运行两个版本
有状态应用 (不推荐用 Deployment)
快速全量更新

4. 更新流程详解

4.1 触发更新

# 方式 1: 修改镜像
kubectl set image deployment/web web=nginx:1.22

# 方式 2: 编辑配置
kubectl edit deployment web

# 方式 3: 应用 YAML
kubectl apply -f deployment.yaml

4.2 更新状态

# 查看更新状态
kubectl rollout status deployment/web

# 输出
Waiting for deployment "web" spec update to be observed...
Waiting for deployment "web" rollout to finish: 1 out of 3 new replicas have been updated...
Waiting for deployment "web" rollout to finish: 2 out of 3 new replicas have been updated...
deployment "web" successfully rolled out

4.3 Deployment Conditions

status:
  conditions:
  - type: Available
    status: "True"
    reason: MinimumReplicasAvailable
  - type: Progressing
    status: "True"
    reason: NewReplicaSetAvailable

Condition	含义
`Available`	最小可用副本已就绪
`Progressing`	正在进行更新
`ReplicaFailure`	创建 Pod 失败

5. 回滚机制

5.1 查看历史

kubectl rollout history deployment/web

# 输出
REVISION  CHANGE-CAUSE
1         <none>
2         kubectl set image deployment/web web=nginx:1.21
3         kubectl set image deployment/web web=nginx:1.22

5.2 记录变更原因

kubectl annotate deployment/web kubernetes.io/change-cause="升级到 v1.22"

5.3 回滚操作

# 回滚到上一版本
kubectl rollout undo deployment/web

# 回滚到指定版本
kubectl rollout undo deployment/web --to-revision=2

# 查看特定版本详情
kubectl rollout history deployment/web --revision=2

5.4 回滚原理

6. 高级发布策略

6.1 蓝绿发布

实现步骤:

部署新版本 (Green) Deployment
验证新版本正常
修改 Service selector 指向新版本
删除旧版本 (Blue) Deployment

# 切换流量
kubectl patch svc web -p '{"spec":{"selector":{"version":"v2"}}}'

6.2 金丝雀发布

基于 Pod 数量:

# Stable: 9 个副本
# Canary: 1 个副本
# 比例约 90:10

基于 Ingress (Nginx):

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    nginx.ingress.kubernetes.io/canary: "true"
    nginx.ingress.kubernetes.io/canary-weight: "10"

6.3 A/B 测试

# 基于 Header
annotations:
  nginx.ingress.kubernetes.io/canary: "true"
  nginx.ingress.kubernetes.io/canary-by-header: "X-Canary"
  nginx.ingress.kubernetes.io/canary-by-header-value: "true"

7. 渐进式交付

7.1 Argo Rollouts

apiVersion: argoproj.io/v1alpha1
kind: Rollout
metadata:
  name: web
spec:
  replicas: 5
  strategy:
    canary:
      steps:
      - setWeight: 20
      - pause: {duration: 1m}
      - setWeight: 40
      - pause: {duration: 1m}
      - setWeight: 60
      - pause: {duration: 1m}
      - setWeight: 80
      - pause: {duration: 1m}
  selector:
    matchLabels:
      app: web
  template:
    # ...

7.2 Flagger

apiVersion: flagger.app/v1beta1
kind: Canary
metadata:
  name: web
spec:
  targetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: web
  progressDeadlineSeconds: 60
  analysis:
    interval: 30s
    threshold: 5
    maxWeight: 50
    stepWeight: 10
    metrics:
    - name: request-success-rate
      thresholdRange:
        min: 99

8. 最佳实践

8.1 就绪探针

# 必须配置, 否则滚动更新可能导致服务中断
readinessProbe:
  httpGet:
    path: /ready
    port: 8080
  initialDelaySeconds: 10
  periodSeconds: 5
  failureThreshold: 3

8.2 优雅关闭

spec:
  terminationGracePeriodSeconds: 60
  containers:
  - lifecycle:
      preStop:
        exec:
          command: ["/bin/sh", "-c", "sleep 10"]

8.3 PodDisruptionBudget

apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: web-pdb
spec:
  minAvailable: 2  # 或 maxUnavailable: 1
  selector:
    matchLabels:
      app: web

8.4 更新建议

实践	说明
设置 minReadySeconds	给应用预热时间
保留足够历史	revisionHistoryLimit >= 10
监控更新过程	观察错误率, 延迟
配合 PDB	保证最小可用数

9. 调试命令

# 查看 Deployment
kubectl get deployment web -o wide
kubectl describe deployment web

# 查看 ReplicaSet
kubectl get rs -l app=web
kubectl describe rs <rs-name>

# 查看更新事件
kubectl get events --field-selector involvedObject.name=web

# 暂停/恢复更新
kubectl rollout pause deployment/web
kubectl rollout resume deployment/web

# 重启 Deployment (触发 Pod 重建)
kubectl rollout restart deployment/web

理解了 Deployment 的副本演进逻辑, 才能在复杂的流量环境下精准控制发布的节奏与安全.

Deployment: 滚动更新与发布策略

On this page