容器编排 -- Deployment

基本概念

  1. Deployment实现了Pod的水平伸缩(horizontal scaling out/in) – 滚动更新(rolling update)
  2. 滚动更新依赖于ReplicaSet
  3. Deployment控制ReplicaSet(版本),ReplicaSet控制Pod(副本数)!!

ReplicaSet

  1. ReplicaSet的定义是Deployment的一个子集
  2. Deployment控制器实际操纵对象是ReplicaSet,而非Pod,Deployment所管理的Pod的ownerReference为ReplicaSet
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apiVersion: apps/v1
kind: ReplicaSet
metadata:
name: nginx-set
labels:
app: nginx
spec:
replicas: 3
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: 'nginx:1.7.9'

Deployment

nginx-deployment.yaml
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apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-deployment
labels:
app: nginx
spec:
replicas: 3
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: 'nginx:1.7.9'
ports:
- containerPort: 80
  1. Deployment、ReplicaSet、Pod三者的关系 – 层层控制
  2. ReplicaSet通过控制器模式,保证系统中Pod的个数永远等于指定的个数
  3. Deployment通过控制器模式,来操作ReplicaSet的数量和属性,进而实现两个编排动作:水平伸缩滚动更新
  4. 水平伸缩:Deployment控制器修改它所控制的ReplicaSet的Pod副本个数即可,ReplicaSet会执行具体的增删Pod操作

水平伸缩 + 滚动更新

创建Deployment

--record:记录每次操作所执行的命令

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# kubectl apply -f nginx-deployment.yaml --record
deployment.apps/nginx-deployment created

查看Deployment – 实时状态

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# kubectl rollout status deployment/nginx-deployment
Waiting for deployment "nginx-deployment" rollout to finish: 0 of 3 updated replicas are available...
Waiting for deployment "nginx-deployment" rollout to finish: 1 of 3 updated replicas are available...
Waiting for deployment "nginx-deployment" rollout to finish: 2 of 3 updated replicas are available...
deployment "nginx-deployment" successfully rolled out

查看Deployment – 当前状态

  1. READY:CURRENT / DESIRED
    • DESIRED:期望的Pod副本数,即spec.replicas
    • CURRENT:当前处于Running状态的Pod数
  2. UP-TO-DATE:当前处于最新版本(Pod对象的Spec部分与Deployment的Pod模板定义完全一致)的Pod数
  3. AVAILABLE:当前可用Running状态 + 最新版本 + 健康检查正确)的Pod数,AVAILABLE是用户期待的最终状态
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# kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
nginx-deployment 3/3 3 3 6s

查看Deployment – 所控制的ReplicaSet

  1. 用户提交Deployment对象后,Deployment控制器会创建一个Pod副本数为3的ReplicaSet
  2. 5d59d67564为pod-template-hash(随机字符串),该随机字符串会加到ReplicaSet所控制的所有Pod的标签里,避免混淆
  3. Deployment只是在ReplicaSet的基础上,添加了UP-TO-DATE字段
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# kubectl get rs
NAME DESIRED CURRENT READY AGE
nginx-deployment-5d59d67564 3 3 3 13m

# kubectl get pods
NAME READY STATUS RESTARTS AGE
nginx-deployment-5d59d67564-2vh6v 1/1 Running 0 17m
nginx-deployment-5d59d67564-fkf98 1/1 Running 0 17m
nginx-deployment-5d59d67564-fw7wc 1/1 Running 0 17m

滚动更新

kubectl edit

原理:把API Object的内容下载到本地文件,修改完后再提交到Kubernetes

升级Nginx

1.7.9 -> 1.9.1

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# kubectl edit deployment/nginx-deployment
...
spec:
containers:
- image: nginx:1.7.9
...
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# kubectl rollout status deployment/nginx-deployment
Waiting for deployment "nginx-deployment" rollout to finish: 1 out of 3 new replicas have been updated...
Waiting for deployment "nginx-deployment" rollout to finish: 1 out of 3 new replicas have been updated...
Waiting for deployment "nginx-deployment" rollout to finish: 1 out of 3 new replicas have been updated...
Waiting for deployment "nginx-deployment" rollout to finish: 2 out of 3 new replicas have been updated...
Waiting for deployment "nginx-deployment" rollout to finish: 2 out of 3 new replicas have been updated...
Waiting for deployment "nginx-deployment" rollout to finish: 2 out of 3 new replicas have been updated...
Waiting for deployment "nginx-deployment" rollout to finish: 1 old replicas are pending termination...
Waiting for deployment "nginx-deployment" rollout to finish: 1 old replicas are pending termination...
deployment "nginx-deployment" successfully rolled out
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# kubectl describe deployment nginx-deployment
...
OldReplicaSets: <none>
NewReplicaSet: nginx-deployment-69c44dfb78 (3/3 replicas created)
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 26m deployment-controller Scaled up replica set nginx-deployment-5d59d67564 to 3
Normal ScalingReplicaSet 57s deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 1
Normal ScalingReplicaSet 55s deployment-controller Scaled down replica set nginx-deployment-5d59d67564 to 2
Normal ScalingReplicaSet 55s deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 2
Normal ScalingReplicaSet 52s deployment-controller Scaled down replica set nginx-deployment-5d59d67564 to 1
Normal ScalingReplicaSet 52s deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 3
Normal ScalingReplicaSet 50s deployment-controller Scaled down replica set nginx-deployment-5d59d67564 to 0
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# kubectl get rs
NAME DESIRED CURRENT READY AGE
nginx-deployment-5d59d67564 0 0 0 28m
nginx-deployment-69c44dfb78 3 3 3 2m44s
  1. 修改Deployment的Pod定义后,Deployment控制器会使用修改后的Pod模板,创建一个新的ReplicaSet(69c44dfb78)
  2. 水平伸缩:旧(3) ==> 新(1) ==> 旧(2) ==> 新(2) ==> 旧(1) ==> 新(3) ==> 旧(0)
  3. Deployment控制器实际控制的是ReplicaSet的数量和属性,一个应用版本对应一个ReplicaSet
    • 而某个版本应用的Pod数量,则由ReplicaSet控制器来保证

水平扩展

只是Pod数量的增减,不会新建ReplicaSet

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# kubectl scale deployment nginx-deployment --replicas=4
deployment.apps/nginx-deployment scaled

# kubectl rollout status deployment/nginx-deployment
Waiting for deployment "nginx-deployment" rollout to finish: 3 of 4 updated replicas are available...
deployment "nginx-deployment" successfully rolled out

# kubectl get rs
NAME DESIRED CURRENT READY AGE
nginx-deployment-5d59d67564 0 0 0 58m
nginx-deployment-69c44dfb78 4 4 4 32m

# kubectl describe deployment nginx-deployment
...
OldReplicaSets: <none>
NewReplicaSet: nginx-deployment-69c44dfb78 (4/4 replicas created)
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 58m deployment-controller Scaled up replica set nginx-deployment-5d59d67564 to 3
Normal ScalingReplicaSet 33m deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 1
Normal ScalingReplicaSet 33m deployment-controller Scaled down replica set nginx-deployment-5d59d67564 to 2
Normal ScalingReplicaSet 33m deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 2
Normal ScalingReplicaSet 33m deployment-controller Scaled down replica set nginx-deployment-5d59d67564 to 1
Normal ScalingReplicaSet 33m deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 3
Normal ScalingReplicaSet 33m deployment-controller Scaled down replica set nginx-deployment-5d59d67564 to 0
Normal ScalingReplicaSet 60s deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 4

版本回滚

  1. 新Pod有问题,滚动更新会停止,允许开发人员和运维人员介入(使用Pod的Health Check,而不是简单依赖容器的Running状态)
  2. Deployment控制器为了保证服务的连续性
    • 在任何时间窗口内,只有指定比例的Pod处于离线状态 – 默认为DESIRED值的25%
    • 在任何时间窗口内,只有指定比例的新Pod被创建出来 – 默认为DESIRED值的25%
    • RollingUpdateStrategy
      • maxSurge:一次滚动中,Deployment控制器可以创建的新Pod数,可以用百分比形式
      • maxUnavailable:一次滚动中,Deployment控制器可以删除的旧Pod数,可以用百分比形式
  3. 命令
    • kubectl set image:直接修改Deployment所使用的镜像
    • kubectl rollout undo:把整个Deployment回滚到上一版本
    • kubectl rollout history:查看每次Deployment变更对应的版本
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apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-deployment
labels:
app: nginx
spec:
...
strategy:
type: RollingUpdate
rollingUpdate:
maxSurge: 1
maxUnavailable: 1

修改为错误的镜像版本(nginx:1.91)

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# kubectl set image deployment/nginx-deployment nginx=nginx:1.91
deployment.apps/nginx-deployment image updated
  1. 新ReplicaSet(停止水平扩展):创建了两个新Pod,状态为Running(CURRENT=2),但并没有进入Ready状态
  2. 旧ReplicaSet(停止水平收缩):删除了一个旧Pod
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# kubectl get rs
NAME DESIRED CURRENT READY AGE
nginx-deployment-5d59d67564 0 0 0 68m
nginx-deployment-69c44dfb78 3 3 3 42m
nginx-deployment-d645d84b6 2 2 0 24s

# kubectl describe deployment nginx-deployment
...
OldReplicaSets: <none>
NewReplicaSet: nginx-deployment-69c44dfb78 (4/4 replicas created)
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 49m deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 1
Normal ScalingReplicaSet 49m deployment-controller Scaled down replica set nginx-deployment-5d59d67564 to 2
Normal ScalingReplicaSet 49m deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 2
Normal ScalingReplicaSet 49m deployment-controller Scaled down replica set nginx-deployment-5d59d67564 to 1
Normal ScalingReplicaSet 49m deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 3
Normal ScalingReplicaSet 49m deployment-controller Scaled down replica set nginx-deployment-5d59d67564 to 0
Normal ScalingReplicaSet 7m25s deployment-controller Scaled up replica set nginx-deployment-d645d84b6 to 1
Normal ScalingReplicaSet 7m25s deployment-controller Scaled down replica set nginx-deployment-69c44dfb78 to 3
Normal ScalingReplicaSet 7m25s deployment-controller Scaled up replica set nginx-deployment-d645d84b6 to 2

回滚到上一版本(旧ReplicaSet扩展为4个,新ReplicaSet收缩为0个)

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# kubectl rollout undo deployment/nginx-deployment
deployment.apps/nginx-deployment rolled back

# kubectl get rs
NAME DESIRED CURRENT READY AGE
nginx-deployment-5d59d67564 0 0 0 72m
nginx-deployment-69c44dfb78 4 4 4 46m
nginx-deployment-d645d84b6 0 0 0 4m54s

# kubectl describe deployment nginx-deployment
...
OldReplicaSets: <none>
NewReplicaSet: nginx-deployment-69c44dfb78 (4/4 replicas created)
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 49m deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 1
Normal ScalingReplicaSet 49m deployment-controller Scaled down replica set nginx-deployment-5d59d67564 to 2
Normal ScalingReplicaSet 49m deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 2
Normal ScalingReplicaSet 49m deployment-controller Scaled down replica set nginx-deployment-5d59d67564 to 1
Normal ScalingReplicaSet 49m deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 3
Normal ScalingReplicaSet 49m deployment-controller Scaled down replica set nginx-deployment-5d59d67564 to 0
Normal ScalingReplicaSet 7m25s deployment-controller Scaled up replica set nginx-deployment-d645d84b6 to 1
Normal ScalingReplicaSet 7m25s deployment-controller Scaled down replica set nginx-deployment-69c44dfb78 to 3
Normal ScalingReplicaSet 7m25s deployment-controller Scaled up replica set nginx-deployment-d645d84b6 to 2
Normal ScalingReplicaSet 2m36s (x2 over 17m) deployment-controller Scaled up replica set nginx-deployment-69c44dfb78 to 4
Normal ScalingReplicaSet 2m36s deployment-controller Scaled down replica set nginx-deployment-d645d84b6 to 0

回滚到特定历史版本

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# kubectl rollout history deployment/nginx-deployment
deployment.apps/nginx-deployment
REVISION CHANGE-CAUSE
1 kubectl apply --filename=nginx-deployment.yaml --record=true
7 kubectl apply --filename=nginx-deployment.yaml --record=true
8 kubectl apply --filename=nginx-deployment.yaml --record=true

# kubectl rollout history deployment/nginx-deployment --revision=1
deployment.apps/nginx-deployment with revision #1
Pod Template:
Labels: app=nginx
pod-template-hash=5d59d67564
Annotations: kubernetes.io/change-cause: kubectl apply --filename=nginx-deployment.yaml --record=true
Containers:
nginx:
Image: nginx:1.7.9
Port: 80/TCP
Host Port: 0/TCP
Environment: <none>
Mounts: <none>
Volumes: <none>

# kubectl get rs
NAME DESIRED CURRENT READY AGE
nginx-deployment-5d59d67564 0 0 0 83m
nginx-deployment-69c44dfb78 4 4 4 57m
nginx-deployment-d645d84b6 0 0 0 15m

# kubectl rollout undo deployment/nginx-deployment --to-revision=1
deployment.apps/nginx-deployment rolled back

# kubectl get rs
NAME DESIRED CURRENT READY AGE
nginx-deployment-5d59d67564 4 4 4 85m
nginx-deployment-69c44dfb78 0 0 0 60m
nginx-deployment-d645d84b6 0 0 0 18m

减少ReplicaSet对象

  1. 默认情况下,每次对Deployment进行一次更新操作,都会生成一个新的ReplicaSet对象
  2. 合并(暂停 & 恢复)
    • 对Deployment的多次更新操作,最终生成一个ReplicaSet对象
    • 命令
      • kubectl rollout pause:让Deployment进入暂停状态,对Deployment的所有修改,都不会触发滚动更新
      • kubectl rollout resume:恢复Deployment,生成一个ReplicaSet对象
  3. 历史版本
    • Deployment.spec.revisionHistoryLimit:Kubernetes为Deployment保留的历史版本数

参考资料

  1. 深入剖析Kubernetes
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