一、知識(shí)準(zhǔn)備
● 本文詳細(xì)探索deployment在滾動(dòng)更新時(shí)候的行為
二、環(huán)境準(zhǔn)備
| 組件 | 版本 |
|---|---|
| OS | Ubuntu 18.04.1 LTS |
| docker | 18.06.0-ce |
三、準(zhǔn)備鏡像
首先準(zhǔn)備2個(gè)不同版本的鏡像，用于測(cè)試（已經(jīng)在阿里云上創(chuàng)建好2個(gè)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(guān)系
+------------+
| deployment |
+-----+------+
|
|
|
|
+--------------------------------------------------+
| | |
| | |
| | |
| | |
| | |
| | |
+------v------+ +------v------+ +------v------+
|replicaset:v1| |replicaset:v2| |replicaset:v3|
+-------------+ +------+------+ +-------------+
|
|
+--------+---------+
| |
| |
+---v---+ +---v---+
|pod:v2 | |pod:v2 |
+-------+ +-------+
● deployment調(diào)度replicaset，pod由replicaset調(diào)度
● deployment管理多個(gè)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(zhǔn)備一個(gè)yaml文件用于測(cè)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(jiǎn)單驗(yàn)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(jīng)正常啟動(dòng)，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(chuàng)建了一個(gè)replicaset，叫做update-deployment-7db77f7cc6（7db77f7cc6是replicaset的template hash值）
● 根據(jù)配置文件的要求，replicaset的副本數(shù)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創(chuàng)建了3個(gè)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創(chuàng)建之后，開(kāi)始分配到worker節(jié)點(diǎn)、拉取鏡像、啟動(dòng)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(xué)要問(wèn)，為什么搞這么復(fù)雜，啟動(dòng)一個(gè)pod需要?jiǎng)佑眠@么多組件呢？下面用一個(gè)場(chǎng)景說(shuō)明為啥需要這么多組件：
鏡像版本更新
● 當(dāng)鏡像版本有更新時(shí)（三種方法都可以實(shí)現(xiàn)，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(wù)可用，又要保證在線更新，流程應(yīng)該是：
??1、先增加一個(gè)pod，鏡像版本為新版本
??2、pod可用之后，刪除一個(gè)老版本pod
??3、循環(huán)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(gè)過(guò)程就是replicaset的作用，它根據(jù)需求，自動(dòng)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(shí)版本需要回退，那replicaset需要把剛才的步驟逆向更新一遍，實(shí)現(xiàn)版本回退
● deployment的作用就是管理replicaset。deployment會(huì)保存各個(gè)版本的replicaset，一旦需要進(jìn)行版本回滾，deployment會(huì)立即回滾replicaset的版本，從而控制pod狀態(tài)
下面測(cè)試一下：
使用patch命令更新鏡像版本，并且使用pause命令來(lái)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(shí)pod狀態(tài)：
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(gè)pod，而刪除了1個(gè)老版本的pod
此時(shí)replicaset狀態(tài)：
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(gè)新版本的replicaset創(chuàng)建了出來(lái)，并且需求的pod數(shù)量為2，而原來(lái)的replicaset需求的pod數(shù)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(gè)版本2
由于使用pause命令，更新過(guò)程到此會(huì)卡主，我們讓更新的過(guò)程繼續(xù)下去：
root@k8s-master:~# kubectl rollout resume deployment update-deployment
deployment.apps "update-deployment" resumed
查看狀態(tài)：
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(jīng)沒(méi)有pod，但是歷史記錄還是保留的，可以通過(guò)deployment調(diào)度快速回滾
五、小結(jié)
● 本文介紹了deployment滾動(dòng)更新時(shí)，deployment、replicaset、pod的細(xì)節(jié)以及創(chuàng)建過(guò)程
● 介紹了deployment版本管理的方式
● 下一小節(jié)將會(huì)介紹在滾動(dòng)更新過(guò)程中最大可用、liveness以及readiness等
至此，本文結(jié)束
在下才疏學(xué)淺，有撒湯漏水的，請(qǐng)各位不吝賜教...
