k8s deployment的滾動更新

一、知識準備

● 本文詳細探索deployment在滾動更新時候的行為

二、環境準備

組件版本

OS	Ubuntu 18.04.1 LTS
docker	18.06.0-ce

三、準備鏡像

首先準備2個不同版本的鏡像，用于測試（已經在阿里云上創建好2個不同版本的nginx鏡像）

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之間的關系

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

● deployment調度replicaset，pod由replicaset調度
● deployment管理多個replicaset版本，可用于回滾
● replicaset控制pod的行為，包括新增pod、刪除pod

我們首先準備一個yaml文件用于測試：

root@k8s-master:~# more roll_update.yaml apiVersion: extensions/v1beta1 kind: Deployment metadata:name: image-deployment spec:replicas: 1template:metadata:labels:app: image-updatespec:containers:- name: nginximage: registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:v1imagePullPolicy: Always

---

簡單驗證一下：

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都已經正常啟動，下面分析一下他們的行為：

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創建了一個replicaset，叫做update-deployment-7db77f7cc6（7db77f7cc6是replicaset的template hash值）
● 根據配置文件的要求，replicaset的副本數為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-7db77f7cc6-7j49gNormal SuccessfulCreate 3m replicaset-controller Created pod: update-deployment-7db77f7cc6-b75wnNormal SuccessfulCreate 3m replicaset-controller Created pod: update-deployment-7db77f7cc6-cfnt5

● replicaset創建了3個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-node2Normal 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 containerNormal Started 9m kubelet, k8s-node2 Started container

● pod被replicaset創建之后，開始分配到worker節點、拉取鏡像、啟動容器等一系列操作
● 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）

---

不禁有同學要問，為什么搞這么復雜，啟動一個pod需要動用這么多組件呢？下面用一個場景說明為啥需要這么多組件：

鏡像版本更新

● 當鏡像版本有更新時（三種方法都可以實現，參考前一篇文章：更新k8s鏡像版本的三種方式），既要保證服務可用，又要保證在線更新，流程應該是：
??1、先增加一個pod，鏡像版本為新版本
??2、pod可用之后，刪除一個老版本pod
??3、循環第1、2步，直到老版本pod全部刪除，新版本的pod全部可用
● 上述的這個過程就是replicaset的作用，它根據需求，自動的增加新版本pod，然后刪除老版本pod，直到老版本pod全部刪除，新版本的pod全部可用
● 如果此時版本需要回退，那replicaset需要把剛才的步驟逆向更新一遍，實現版本回退
● deployment的作用就是管理replicaset。deployment會保存各個版本的replicaset，一旦需要進行版本回滾，deployment會立即回滾replicaset的版本，從而控制pod狀態

---

下面測試一下：

使用patch命令更新鏡像版本，并且使用pause命令來觀察：

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

此時pod狀態：

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個pod，而刪除了1個老版本的pod

此時replicaset狀態：

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

有一個新版本的replicaset創建了出來，并且需求的pod數量為2，而原來的replicaset需求的pod數量從3降為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

新增了一個版本2

由于使用pause命令，更新過程到此會卡主，我們讓更新的過程繼續下去：

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

查看狀態：

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已經沒有pod，但是歷史記錄還是保留的，可以通過deployment調度快速回滾

五、小結

● 本文介紹了deployment滾動更新時，deployment、replicaset、pod的細節以及創建過程
● 介紹了deployment版本管理的方式

參考鏈接：https://www.cnblogs.com/wangkun122/articles/12707216.html

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