Kubernetes入门实战(3)：运维之扩容与升级
本文我们将对Kubernetes的常用运维操作扩容与升级做简单说明。
1. Node的扩容
Node的扩容简单言之就是增加新的Node节点。在节点上安装Kubelet，Kube-proxy及Docker, 并修改参数使其指向Master地址。基于Kuberlet的自动注册机制，新的Node将会自动加入现有的Kubernetes集群中。
2. Pod的动态扩容和缩放
在实际运维过程中，我们常常需要对某个服务动态扩容以满足突增的流量，或者动态减少服务实例节约服务器资源。
下面我们将动态增加redis-slave的pod副本由2个增加为3个。
#kubectl scale rc redis-slave --replicas=3
[root@localhost ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
frontend-ob32o 1/1 Running 1 30d
frontend-zcyms 1/1 Running 1 30d
frontend-zllt8 1/1 Running 1 30d
redis-master-gjkqh 1/1 Running 1 30d
redis-slave-geq4m 1/1 Running 1 30d
redis-slave-o692g 1/1 Running 1 30d
[root@localhost ~]# kubectl scale rc redis-slave --replicas=3
scaled
[root@localhost ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
frontend-ob32o 1/1 Running 1 30d
frontend-zcyms 1/1 Running 1 30d
frontend-zllt8 1/1 Running 1 30d
redis-master-gjkqh 1/1 Running 1 30d
redis-slave-geq4m 1/1 Running 1 30d
redis-slave-o692g 1/1 Running 1 30d
redis-slave-qozrp 0/1 Running 0 6s
同样的我们也可以减少pod的副本，以下我们将redis-slave由3个副本减为1个。
[root@localhost ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
frontend-ob32o 1/1 Running 1 30d
frontend-zcyms 1/1 Running 1 30d
frontend-zllt8 1/1 Running 1 30d
redis-master-gjkqh 1/1 Running 1 30d
redis-slave-geq4m 1/1 Running 1 30d
redis-slave-o692g 1/1 Running 1 30d
redis-slave-qozrp 1/1 Running 0 2m
[root@localhost ~]# kubectl scale rc redis-slave --replicas=1
scaled
[root@localhost ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
frontend-ob32o 1/1 Running 1 30d
frontend-zcyms 1/1 Running 1 30d
frontend-zllt8 1/1 Running 1 30d
redis-master-gjkqh 1/1 Running 1 30d
redis-slave-qozrp 1/1 Running 0 2m
3. 应用的滚动升级
在实际运维过程中，如何不停止服务而进行升级将变得越来越常见，Kubernetes提供了Rolling-update的功能来解决上述场景。
我们假设PHP的image有一个新的v2版本，我们需要将现有PHP服务滚动升级为v2。
3.1 制作新镜像
简单起见，我们通过docker commit来制作一个新镜像，首先用原镜像启动一个新容器，你可以在容器里修改，然后退出。
docker run -it docker.io/kubeguide/guestbook-php-frontend /bin/bash
root@1b605f52b5f1:/var/www/html# exit
exit
好，现在我们用docker commit来保存刚才我们编辑过的容器,我们把它命名为guestbook-php-frontend:v2
[root@localhost ~]# docker commit 1b605f52b5f1 guestbook-php-frontend:v2
103579c2c2774b62017de760475e7a1ae3addacc9f1c88ea59ec1f3280ae93fb
[root@localhost ~]# docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
guestbook-php-frontend v2 103579c2c277 5 seconds ago 509.6 MB
docker.io/kubeguide/guestbook-php-frontend latest 38658844a359 5 months ago 509.6 MB
docker.io/kubeguide/redis-master latest 423e126c2ad4 6 months ago 419.1 MB
docker.io/kubeguide/guestbook-redis-slave latest 5429ea4e7990 6 months ago 109.5 MB
gcr.io/google_containers/pause 0.8.0 2c40b0526b63 11 months ago 241.7 kB
我们看到新增加了一个镜像guestbook-php-frontend，tag为v2，接下来我们将通过两种方法来演示滚动升级。
3.2 通过配置文件
创建 frontend-controller-v2.yaml
apiVersion: v1
kind: ReplicationController
metadata:
name: frontend-v2
labels:
name: frontend
spec:
replicas: 3
selector:
name: frontend-v2
template:
metadata:
labels:
name: frontend-v2
spec:
containers:
- name: php-redis
image: guestbook-php-frontend:v2
env:
- name: GET_HOSTS_FROM
value: env
ports:
- containerPort: 80
Kubectl的执行过程如下：
[root@localhost ~]# kubectl rolling-update frontend -f frontend-controller-v2.yaml
Creating frontend-v2
At beginning of loop: frontend replicas: 2, frontend-v2 replicas: 1
Updating frontend replicas: 2, frontend-v2 replicas: 1
At end of loop: frontend replicas: 2, frontend-v2 replicas: 1
At beginning of loop: frontend replicas: 1, frontend-v2 replicas: 2
Updating frontend replicas: 1, frontend-v2 replicas: 2
At end of loop: frontend replicas: 1, frontend-v2 replicas: 2
At beginning of loop: frontend replicas: 0, frontend-v2 replicas: 3
Updating frontend replicas: 0, frontend-v2 replicas: 3
At end of loop: frontend replicas: 0, frontend-v2 replicas: 3
Update succeeded. Deleting frontend
frontend-v2
查看pods创建过程, 我们看到新的POD副本从1开始增加，旧的POD副本从3逐步减少，最终旧的POD副本被删除。这样就完成了应用的升级。
[root@localhost ~]# kubectl get rc
CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
frontend php-redis docker.io/kubeguide/guestbook-php-frontend name=frontend 3
frontend-v2 php-redis guestbook-php-frontend:v2 name=frontend-v2 1
[root@localhost ~]# kubectl get rc
CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
frontend php-redis docker.io/kubeguide/guestbook-php-frontend name=frontend 2
frontend-v2 php-redis guestbook-php-frontend:v2 name=frontend-v2 2
[root@localhost ~]# kubectl get rc
CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
frontend php-redis docker.io/kubeguide/guestbook-php-frontend name=frontend 1
frontend-v2 php-redis guestbook-php-frontend:v2 name=frontend-v2 3
[root@localhost ~]# kubectl get rc
CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
frontend-v2 php-redis guestbook-php-frontend:v2 name=frontend-v2 3
3.3 通过新版镜像
另一种方法是不使用配置文件，直接用kubectl rolling-update 加上–image参数指定新版镜像名称来滚动升级
kubectl rolling-update frontend --image=guestbook-php-frontend:v2
[root@localhost ~]# kubectl rolling-update frontend --image=guestbook-php-frontend:v2
Creating frontend-cdb7f26e49a90eae43e257284310b1cf
At beginning of loop: frontend replicas: 2, frontend-cdb7f26e49a90eae43e257284310b1cf replicas: 1
Updating frontend replicas: 2, frontend-cdb7f26e49a90eae43e257284310b1cf replicas: 1
At end of loop: frontend replicas: 2, frontend-cdb7f26e49a90eae43e257284310b1cf replicas: 1
At beginning of loop: frontend replicas: 1, frontend-cdb7f26e49a90eae43e257284310b1cf replicas: 2
Updating frontend replicas: 1, frontend-cdb7f26e49a90eae43e257284310b1cf replicas: 2
At end of loop: frontend replicas: 1, frontend-cdb7f26e49a90eae43e257284310b1cf replicas: 2
At beginning of loop: frontend replicas: 0, frontend-cdb7f26e49a90eae43e257284310b1cf replicas: 3
Updating frontend replicas: 0, frontend-cdb7f26e49a90eae43e257284310b1cf replicas: 3
At end of loop: frontend replicas: 0, frontend-cdb7f26e49a90eae43e257284310b1cf replicas: 3
Update succeeded. Deleting old controller: frontend
Renaming frontend-cdb7f26e49a90eae43e257284310b1cf to frontend
frontend
更新完成，查看RC，我们看到与配置文件不同，Kubectl给rc增加了一个key为”deployment”的label，当然这个名字可以通过–deployment-label-key参数修改。
[root@localhost ~]# kubectl get rc
CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
frontend php-redis guestbook-php-frontend:v2 deployment=cdb7f26e49a90eae43e257284310b1cf,name=frontend 3
如果在更新过程中发现配置错误，可以通过执行kubectl rolling-update --rollback完成回滚kubectl rolling-update frontend --image=guestbook-php-frontend:v2 --rollback