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
| 元件 | 版本 |
|---|---|
| OS | Ubuntu 18.04.1 LTS |
| docker | 18.06.0-ce |
三、準備映象
首先準備2個不同版本的映象，用於測試（已經在阿里雲上建立好2個不同版本的nginx映象）
docker pull registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:v1
docker pull registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:v2root@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之間的關係
+------------+
| deployment |
+-----+------+
|
|
|
|
+--------------------------------------------------+
| | |
| | |
| | |
| | |
| | |
| | |
+------v------+ +------v------+ +------v------+
|replicaset:v1| |replicaset:v2| |replicaset:v3|
+-------------+ +------+------+ +-------------+
|
|
+--------+---------+
| |
| |
+---v---+ +---v---+
|pod:v2 | |pod:v2 |
+-------+ +-------+
● deployment排程replicaset，pod由replicaset排程
● deployment管理多個replicaset版本，可用於回滾
● replicaset控制pod的行為，包括新增pod、刪除pod
我們首先準備一個yaml檔案用於測試：
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簡單驗證一下：
root@k8s-master:~# kubectl apply -f roll_update.yaml
deployment.extensions "update-deployment" createdroot@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 1mdeployment、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建立了一個replicaset，叫做update-deployment-7db77f7cc6（7db77f7cc6是replicaset的template hash值）
● 根據配置檔案的要求，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-7db77f7cc6-7j49g
Normal SuccessfulCreate 3m replicaset-controller Created pod: update-deployment-7db77f7cc6-b75wn
Normal SuccessfulCreate 3m replicaset-controller Created pod: update-deployment-7db77f7cc6-cfnt5● replicaset建立了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-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建立之後，開始分配到worker節點、拉取映象、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，為什麼搞這麼複雜，啟動一個pod需要動用這麼多元件呢？下面用一個場景說明為啥需要這麼多元件：
映象版本更新
● 當映象版本有更新時（三種方法都可以實現，參考前一篇文章：更新k8s映象版本的三種方式），既要保證服務可用，又要保證線上更新，流程應該是：
1、先增加一個pod，映象版本為新版本
2、pod可用之後，刪除一個老版本pod
3、迴圈第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，然後刪除老版本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會儲存各個版本的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命令更新映象版本，並且使用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建立了出來，並且需求的pod數量為2，而原來的replicaset需求的pod數量從3降為2
檢視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
由於使用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檢視狀態：
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=3963606113v1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排程快速回滾
五、小結
● 本文介紹了deployment滾動更新時，deployment、replicaset、pod的細節以及建立過程
● 介紹了deployment版本管理的方式
● 下一小節將會介紹在滾動更新過程中最大可用、liveness以及readiness等
至此，本文結束
在下才疏學淺，有撒湯漏水的，請各位不吝賜教…