详解k8s deployment的滚动更新

清疚 2023-10-03 14:17 30阅读 0赞

## k8s deployment的滚动更新 ##

> #### 一、知识准备 ####

● 本文详细探索deployment在滚动更新时候的行为

> #### 二、环境准备 ####

<table> 
 <thead> 
  <tr> 
   <th>组件</th> 
   <th>版本</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>OS</td> 
   <td>Ubuntu 18.04.1 LTS</td> 
  </tr> 
  <tr> 
   <td>docker</td> 
   <td>18.06.0-ce</td> 
  </tr> 
 </tbody> 
</table>

> #### 三、准备镜像 ####

首先准备2个不同版本的镜像，用于测试（已经在阿里云上创建好2个不同版本的nginx镜像）

docker pull registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:v1
    docker pull registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:v2
    root@k8s-master:~# docker run -d --rm -p 10080:80 nginx:v1
    e88097841c5feef92e4285a2448b943934ade5d86412946bc8d86e262f80a050
    root@k8s-master:~# curl http://127.0.0.1:10080
    ----------
    version: v1
    hostname: f5189a5d3ad3

> #### 四、deployment、replicaset、pod之间的关系 ####

+------------+
                               | deployment |
                               +-----+------+
                                     |
                                     |
                                     |
                                     |
           +--------------------------------------------------+
           |                         |                        |
           |                         |                        |
           |                         |                        |
           |                         |                        |
           |                         |                        |
           |                         |                        |
    +------v------+           +------v------+          +------v------+
    |replicaset:v1|           |replicaset:v2|          |replicaset:v3|
    +-------------+           +------+------+          +-------------+
                                     |
                                     |
                            +--------+---------+
                            |                  |
                            |                  |
                        +---v---+          +---v---+
                        |pod:v2 |          |pod:v2 |
                        +-------+          +-------+

● deployment调度replicaset，pod由replicaset调度  
● deployment管理多个replicaset版本，可用于回滚  
● replicaset控制pod的行为，包括新增pod、删除pod

我们首先准备一个yaml文件用于测试：

root@k8s-master:~# more roll_update.yaml
    apiVersion: extensions/v1beta1
    kind: Deployment
    metadata:
      name: image-deployment
    spec:
      replicas: 1
      template:
        metadata:
          labels:
            app: image-update
        spec:
          containers:
          - name: nginx
            image: registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:v1
            imagePullPolicy: Always

--------------------

简单验证一下：

root@k8s-master:~# kubectl apply -f roll_update.yaml
    deployment.extensions "update-deployment" created
    root@k8s-master:~# kubectl get deploy
    NAME                DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
    update-deployment   3         3         3            3           54s
    root@k8s-master:~# kubectl get rs
    NAME                           DESIRED   CURRENT   READY     AGE
    update-deployment-7db77f7cc6   3         3         3         56s
    root@k8s-master:~# kubectl get pod
    NAME                                 READY     STATUS    RESTARTS   AGE
    update-deployment-7db77f7cc6-7j49g   1/1       Running   0          1m
    update-deployment-7db77f7cc6-b75wn   1/1       Running   0          1m
    update-deployment-7db77f7cc6-cfnt5   1/1       Running   0          1m

deployment、replicaset、pod都已经正常启动，下面分析一下他们的行为：

deployment

root@k8s-master:~# kubectl describe deploy update-deployment
    Name:                   update-deployment
    Namespace:              default
    ...
    Replicas:               3 desired | 3 updated | 3 total | 3 available | 0 unavailable
    StrategyType:           RollingUpdate
    MinReadySeconds:        0
    RollingUpdateStrategy:  1 max unavailable, 1 max surge
    ...
    NewReplicaSet:   update-deployment-7db77f7cc6 (3/3 replicas created)
    Events:
      Type    Reason             Age   From                   Message
      ----    ------             ----  ----                   -------
      Normal  ScalingReplicaSet  1m    deployment-controller  Scaled up replica set update-deployment-7db77f7cc6 to 3

● deployment创建了一个replicaset，叫做update-deployment-7db77f7cc6（7db77f7cc6是replicaset的template hash值）  
● 根据配置文件的要求，replicaset的副本数为3

--------------------

replicaset

root@k8s-master:~# kubectl describe rs update-deployment-7db77f7cc6
    Name:           update-deployment-7db77f7cc6
    Namespace:      default
    ...
    Controlled By:  Deployment/update-deployment
    Replicas:       3 current / 3 desired
    Pods Status:    3 Running / 0 Waiting / 0 Succeeded / 0 Failed
    ...
    Events:
      Type    Reason            Age   From                   Message
      ----    ------            ----  ----                   -------
      Normal  SuccessfulCreate  3m    replicaset-controller  Created pod: update-deployment-7db77f7cc6-7j49g
      Normal  SuccessfulCreate  3m    replicaset-controller  Created pod: update-deployment-7db77f7cc6-b75wn
      Normal  SuccessfulCreate  3m    replicaset-controller  Created pod: update-deployment-7db77f7cc6-cfnt5

● replicaset创建了3个pod

--------------------

pod

root@k8s-master:~# kubectl describe pod update-deployment-7db77f7cc6-7j49g
    Name:           update-deployment-7db77f7cc6-7j49g
    Namespace:      default
    ...
    Status:         Running
    IP:             10.10.169.140
    Controlled By:  ReplicaSet/update-deployment-7db77f7cc6
    ...
    Events:
      Type    Reason                 Age   From                Message
      ----    ------                 ----  ----                -------
      Normal  Scheduled              9m    default-scheduler   Successfully assigned update-deployment-7db77f7cc6-7j49g to k8s-node2
      Normal  SuccessfulMountVolume  9m    kubelet, k8s-node2  MountVolume.SetUp succeeded for volume "default-token-v9nkm"
      Normal  Pulling                9m    kubelet, k8s-node2  pulling image "registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:v1"
      Normal  Pulled                 9m    kubelet, k8s-node2  Successfully pulled image "registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:v1"
      Normal  Created                9m    kubelet, k8s-node2  Created container
      Normal  Started                9m    kubelet, k8s-node2  Started container

● pod被replicaset创建之后，开始分配到worker节点、拉取镜像、启动容器等一系列操作  
● 所以pod的命名方式是：update-deployment-7db77f7cc6-7j49g（deployment名字-replicaset模板hash名字-pod模板hash名字）

--------------------

不禁有同学要问，为什么搞这么复杂，启动一个pod需要动用这么多组件呢？下面用一个场景说明为啥需要这么多组件：

> ##### 镜像版本更新 #####

● 当镜像版本有更新时（三种方法都可以实现，参考前一篇文章：[更新k8s镜像版本的三种方式][k8s]），既要保证服务可用，又要保证在线更新，流程应该是：  
  1、先增加一个pod，镜像版本为新版本  
  2、pod可用之后，删除一个老版本pod  
  3、循环第1、2步，直到老版本pod全部删除，新版本的pod全部可用  
● 上述的这个过程就是replicaset的作用，它根据需求，自动的增加新版本pod，然后删除老版本pod，直到老版本pod全部删除，新版本的pod全部可用  
● 如果此时版本需要回退，那replicaset需要把刚才的步骤逆向更新一遍，实现版本回退  
● deployment的作用就是管理replicaset。deployment会保存各个版本的replicaset，一旦需要进行版本回滚，deployment会立即回滚replicaset的版本，从而控制pod状态

--------------------

下面测试一下：

使用patch命令更新镜像版本，并且使用pause命令来观察：

root@k8s-master:~# kubectl patch deployment update-deployment \
    --patch '{"spec": {"template": {"spec": {"containers": [{"name": "nginx","image":"registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:v2"}]}}}}' \
    && kubectl rollout pause deployment update-deployment
    deployment.extensions "update-deployment" patched
    deployment.apps "update-deployment" paused

此时pod状态：

root@k8s-master:~# kubectl get pod -owide
    NAME                                 READY     STATUS        RESTARTS   AGE       IP              NODE
    update-deployment-7db77f7cc6-7j49g   1/1       Running       0          1h        10.10.169.140   k8s-node2
    update-deployment-7db77f7cc6-b75wn   1/1       Running       0          1h        10.10.235.211   k8s-master
    update-deployment-7db77f7cc6-cfnt5   1/1       Terminating   0          1h        10.10.36.126    k8s-node1
    update-deployment-7fb7b4b557-6987x   1/1       Running       0          7s        10.10.36.127    k8s-node1
    update-deployment-7fb7b4b557-dxdqb   1/1       Running       0          10s       10.10.169.139   k8s-node2

新增了2个pod，而删除了1个老版本的pod

此时replicaset状态：

root@k8s-master:~# kubectl get rs -owide
    NAME                           DESIRED   CURRENT   READY     AGE       CONTAINERS   IMAGES                                                   SELECTOR
    update-deployment-7db77f7cc6   2         2         2         1h        nginx        registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:v1   app=roll-update,pod-template-hash=3863393772
    update-deployment-7fb7b4b557   2         2         2         4m        nginx        registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:v2   app=roll-update,pod-template-hash=3963606113

有一个新版本的replicaset创建了出来，并且需求的pod数量为2，而原来的replicaset需求的pod数量从3降为2

查看replicaset版本：

root@k8s-master:~# kubectl rollout history deploy update-deployment
    deployments "update-deployment"
    REVISION  CHANGE-CAUSE
    1         <none>
    2         update version to v2

新增了一个版本`2`

由于使用pause命令，更新过程到此会卡主，我们让更新的过程继续下去：

root@k8s-master:~# kubectl rollout resume deployment update-deployment
    deployment.apps "update-deployment" resumed

查看状态：

root@k8s-master:~# kubectl get pod
    NAME                                 READY     STATUS    RESTARTS   AGE
    update-deployment-7fb7b4b557-6987x   1/1       Running   0          15m
    update-deployment-7fb7b4b557-dxdqb   1/1       Running   0          15m
    update-deployment-7fb7b4b557-wg5c8   1/1       Running   0          1m
    root@k8s-master:~# kubectl get rs -owide
    NAME                           DESIRED   CURRENT   READY     AGE       CONTAINERS   IMAGES                                                   SELECTOR
    update-deployment-7db77f7cc6   0         0         0         1h        nginx        registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:v1   app=roll-update,pod-template-hash=3863393772
    update-deployment-7fb7b4b557   3         3         3         14m       nginx        registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:v2   app=roll-update,pod-template-hash=3963606113

v1版本的replicaset已经没有pod，但是历史记录还是保留的，可以通过deployment调度快速回滚

> #### 五、小结 ####

● 本文介绍了deployment滚动更新时，deployment、replicaset、pod的细节以及创建过程  
● 介绍了deployment版本管理的方式

参考链接：https://www.cnblogs.com/wangkun122/articles/12707216.html

[k8s]: https://www.cnblogs.com/MrVolleyball/p/10315698.html