一、知识准备
● 本文详细探索deployment在滚动更新时候的行为
● 相关的参数介绍:
livenessProbe:存活性探测。判断pod是否已经停止
readinessProbe:就绪性探测。判断pod是否能够提供正常服务
maxSurge:在滚动更新过程中最多可以存在的pod数
maxUnavailable:在滚动更新过程中最多不可用的pod数
二、环境准备
组件 版本 OS Ubuntu 18.04.1 LTS docker 18.06.0-ce
三、准备镜像、yaml文件
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:delay_v1
2个镜像都提供相同的服务,只不过 nginx:delay_v1
会延迟启动20才启动nginx
root@k8s-master:~# docker run -d --rm -p 10080:80 nginx:v1
e88097841c5feef92e4285a2448b943934ade5d86412946bc8d86e262f80a050
root@k8s-master:~# curl http://127.0.0.1:10080
apiVersion: v1
kind: Service
metadata:
name: nginx-service
spec:
selector:
app: roll-update
ports:
- protocol: TCP
port: 10080
targetPort: 80
四、livenessProbe与readinessProbe
livenessProbe:存活性探测,最主要是用来探测pod是否需要重启
readinessProbe:就绪性探测,用来探测pod是否已经能够提供服务
● 在滚动更新的过程中,pod会动态的被delete,然后又被create出来。存活性探测保证了始终有足够的pod存活提供服务,一旦出现pod数量不足,k8s会立即拉起新的pod
● 但是在pod启动的过程中,服务正在打开,并不可用,这时候如果有流量打过来,就会造成报错
下面来模拟一下这个场景:
首先apply上述的配置文件
root@k8s-master:~# kubectl apply -f roll_update.yaml
deployment.extensions "update-deployment" created
service "nginx-service" created
root@k8s-master:~# kubectl get pod -owide
NAME READY STATUS RESTARTS AGE IP NODE
update-deployment-7db77f7cc6-c4s2v 1/1 Running 0 28s 10.10.235.232 k8s-master
update-deployment-7db77f7cc6-nfgtd 1/1 Running 0 28s 10.10.36.82 k8s-node1
update-deployment-7db77f7cc6-tflfl 1/1 Running 0 28s 10.10.169.158 k8s-node2
root@k8s-master:~# kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
nginx-service ClusterIP 10.254.254.199 <none> 10080/TCP 1m
</none>
重新打开终端,测试当前服务的可用性(每秒做一次循环去获取nginx的服务内容):
root@k8s-master:~# while :; do curl http://10.254.254.199:10080; sleep 1; done
version: v1
hostname: update-deployment-7db77f7cc6-c4s2v
version: v1
hostname: update-deployment-7db77f7cc6-nfgtd
...
这时候把镜像版本更新到nginx:delay_v1,这个镜像会延迟启动nginx,也就是说,会先sleep 20s,然后才去启动nginx服务。这就模拟了在服务启动过程中,虽然pod已经是存在的状态,但是并没有真正提供服务
root@k8s-master:~# kubectl patch deployment update-deployment --patch '{"metadata":{"annotations":{"kubernetes.io/change-cause":"update version to v2"}} ,"spec": {"template": {"spec": {"containers": [{"name": "nginx","image":"registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:delay_v1"}]}}}}'
deployment.extensions "update-deployment" patched
...
version: delay_v1
hostname: update-deployment-d788c7dc6-6th87
version: delay_v1
hostname: update-deployment-d788c7dc6-njmpz
apiVersion: v1
kind: Service
metadata:
name: nginx-service
spec:
selector:
app: roll-update
ports:
- protocol: TCP
port: 10080
targetPort: 80
重复上述步骤,先创建 nginx:v1
,然后patch到 nginx:delay_v1
root@k8s-master:~# kubectl apply -f roll_update.yaml
deployment.extensions "update-deployment" created
service "nginx-service" created
root@k8s-master:~# kubectl patch deployment update-deployment --patch '{"metadata":{"annotations":{"kubernetes.io/change-cause":"update version to v2"}} ,"spec": {"template": {"spec": {"containers": [{"name": "nginx","image":"registry.cn-beijing.aliyuncs.com/mrvolleyball/nginx:delay_v1"}]}}}}'
deployment.extensions "update-deployment" patched
root@k8s-master:~# kubectl get pod -owide
NAME READY STATUS RESTARTS AGE IP NODE
busybox 1/1 Running 0 45d 10.10.235.255 k8s-master
lifecycle-demo 1/1 Running 0 32d 10.10.169.186 k8s-node2
private-reg 1/1 Running 0 92d 10.10.235.209 k8s-master
update-deployment-54d497b7dc-4mlqc 0/1 Running 0 13s 10.10.169.178 k8s-node2
update-deployment-54d497b7dc-pk4tb 0/1 Running 0 13s 10.10.36.98 k8s-node1
update-deployment-6d5d7c9947-l7dkb 1/1 Terminating 0 1m 10.10.169.177 k8s-node2
update-deployment-6d5d7c9947-pbzmf 1/1 Running 0 1m 10.10.36.97 k8s-node1
update-deployment-6d5d7c9947-zwt4z 1/1 Running 0 1m 10.10.235.246 k8s-master
● 由于设置了readinessProbe,虽然pod已经启动起来了,但是并不会立即投入使用,所以出现了 READY: 0/1
的情况
● 并且有pod出现了一直持续 Terminating
状态,因为滚动更新的限制,至少要保证有pod可用
再查看curl的状态,image的版本平滑更新到了 nginx:delay_v1
,没有出现报错的状况
`
root@k8s-master:~# while :; do curl http://10.254.66.136:10080; sleep 1; done
…
version: v1
hostname: update-deployment-6d5d7c9947-pbzmf
version: v1
hostname: update-deployment-6d5d7c9947-pbzmf
version: delay_v1
hostname: update-deployment-54d497b7dc-pk4tb
version: delay_v1
hostname: update-deployment-54d497b7dc-pk4tb
Original: https://www.cnblogs.com/MrVolleyball/p/10360860.html
Author: wilson排球
Title: 详细聊聊k8s deployment的滚动更新(二)
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