聊聊kubernetes——跑个应用
kubernetes学习笔记，分享出来，希望能帮助一些有需要的人，有问题一起交流。
本文是带领大家一起用kubernetes跑个应用，体验一下kubernetes。
1. 使用官网交互环境跑个应用
去官网，进入kubernetes交互环境。
顺序执行以下命令
# 启动kubernetes
$ minikube start
# 查看nodes信息
$ kubectl get nodes
# 查看cluster（集群）信息
$ kubectl cluster-info
# 跑个应用
$ kubectl run kubernetes-bootcamp --image=docker.io/jocatalin/kubernetes-bootcamp:v1 --port=8080
最后会输出：deployment.apps "kubernetes-bootcamp" created，说明我们应用跑起来了。
查看Pod：
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-56cdd766d-zjx5j 1/1 Running 0 3m
kubernetes-bootcamp-56cdd766d-zjx5就是应用所在的Pod
默认情况下Pod只能在集群（cluster）内部访问，外部要访问应用需要通过service暴露的端口来访问。
使用service暴露应用，使得外部可以访问：
$ kubectl expose deployment/kubernetes-bootcamp --type="NodePort" --port 8080
输出：service "kubernetes-bootcamp" exposed
查看以下services：
$ kubectl get services
看一下结果：
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 12m
kubernetes-bootcamp NodePort 10.103.30.96 <none> 8080:30623/TCP 40s
kubernetes是默认的service，我们暂且不管，kubernetes-bootcamp就是我们应用的service。8080:30623 后面的端口30623是随机分配的。
2. Scale 应用
默认情况下应用只有一个副本，通过kubectl get deployments命令查看副本的情况：
$ kubectl get deployments
结果：
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
kubernetes-bootcamp 1 1 1 1 11m
我们看到了1个副本。
通过以下命令增加副本：
$ kubectl scale deployments/kubernetes-bootcamp --replicas=3
输出：deployment.extensions "kubernetes-bootcamp" scaled
然后，查看现在的副本：
$ kubectl get deployments
结果：
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
kubernetes-bootcamp 3 3 3 3 15m
看到了3个副本，扩容速度很快的。
kubectl get pods命令查看我们的pods
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-56cdd766d-f74cg 1/1 Running 0 1m
kubernetes-bootcamp-56cdd766d-zjx5j 1/1 Running 0 11m
kubernetes-bootcamp-56cdd766d-8sdjc 1/1 Running 0
1m
通过curl nodeName:port来访问应用：
$ curl minikube:30623
Hello Kubernetes bootcamp! | Running on: kubernetes-bootcamp-56cdd766d-zjx5j |v=1
$ curl minikube:30623
Hello Kubernetes bootcamp! | Running on: kubernetes-bootcamp-56cdd766d-f74cg |v=1
$ curl minikube:30623
Hello Kubernetes bootcamp! | Running on: kubernetes-bootcamp-56cdd766d-zjx5j |v=1
$ curl minikube:30623
Hello Kubernetes bootcamp! | Running on: kubernetes-bootcamp-56cdd766d-f74cg |v=1
$ curl minikube:30623
Hello Kubernetes bootcamp! | Running on: kubernetes-bootcamp-56cdd766d-8sdjc |v=1
$
看以上结果，发现应用自动负载均衡了。
其中minikube:30623 中的minikube是我们的node名称，通过kubectl get nodes获取的。
我们来试一下减少副本：
$ kubectl scale deployments/kubernetes-bootcamp --replicas=2
输出：deployment.extensions "kubernetes-bootcamp" scaled
同样的命令，只是改变了一下--replicas的参数
这时候来看一下当前的pods：
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-56cdd766d-f74cg 1/1 Running 0 7m
kubernetes-bootcamp-56cdd766d-zjx5j 1/1 Running 0 22m
发现少了一个应用（pods）kubernetes-bootcamp-56cdd766d-8sdjc
3. 应用更新
应用升级
为了演示应用更新，我们将副本设置为5个，来看看应用更新过程
$ kubectl scale deployments/kubernetes-bootcamp --replicas=5
deployment.extensions "kubernetes-bootcamp" scaled
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-56cdd766d-722v7 1/1 Running 0 12s
kubernetes-bootcamp-56cdd766d-f74cg 1/1 Running 0 12m
kubernetes-bootcamp-56cdd766d-vft4v 1/1 Running 0 12s
kubernetes-bootcamp-56cdd766d-z525n 1/1 Running 0 12s
kubernetes-bootcamp-56cdd766d-zjx5j 1/1 Running 0 26m
这时候已经运行了5个副本，下一步开始更新应用，我们用到了镜像v2版本：
$ kubectl set image deployments/kubernetes-bootcamp kubernetes-bootcamp=docker.io/jocatalin/kubernetes-bootcamp:v2
deployment.apps "kubernetes-bootcamp" image updated
$ kubectl get podsNAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-56cdd766d-722v7 1/1 Terminating 0 2m
kubernetes-bootcamp-56cdd766d-f74cg 1/1 Terminating 0 14m
kubernetes-bootcamp-56cdd766d-vft4v 1/1 Terminating 0 2m
kubernetes-bootcamp-56cdd766d-z525n 1/1 Terminating 0 2m
kubernetes-bootcamp-56cdd766d-zjx5j 1/1 Running 0 29m
kubernetes-bootcamp-5bddb78d8f-7b2jr 0/1 Pending 0 3s
kubernetes-bootcamp-5bddb78d8f-c75zp 1/1 Running 0 5s
kubernetes-bootcamp-5bddb78d8f-g5mc7 0/1 ContainerCreating 0 3s
kubernetes-bootcamp-5bddb78d8f-hlndn 1/1 Running 0 4s
kubernetes-bootcamp-5bddb78d8f-w6s4s 1/1 Running 0 5s
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-56cdd766d-722v7 1/1 Terminating 0 2m
kubernetes-bootcamp-56cdd766d-f74cg 1/1 Terminating 0 14m
kubernetes-bootcamp-56cdd766d-vft4v 1/1 Terminating 0 2m
kubernetes-bootcamp-56cdd766d-z525n 1/1 Terminating 0 2m
kubernetes-bootcamp-56cdd766d-zjx5j 1/1 Terminating 0 29m
kubernetes-bootcamp-5bddb78d8f-7b2jr 1/1 Running 0 12s
kubernetes-bootcamp-5bddb78d8f-c75zp 1/1 Running 0 14s
kubernetes-bootcamp-5bddb78d8f-g5mc7 1/1 Running 0 12s
kubernetes-bootcamp-5bddb78d8f-hlndn 1/1 Running 0 13s
kubernetes-bootcamp-5bddb78d8f-w6s4s 1/1 Running 0 14s
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-56cdd766d-722v7 1/1 Terminating 0 2m
kubernetes-bootcamp-56cdd766d-f74cg 1/1 Terminating 0 14m
kubernetes-bootcamp-56cdd766d-vft4v 1/1 Terminating 0 2m
kubernetes-bootcamp-56cdd766d-z525n 1/1 Terminating 0 2m
kubernetes-bootcamp-56cdd766d-zjx5j 1/1 Terminating 0 29m
kubernetes-bootcamp-5bddb78d8f-7b2jr 1/1 Running 0 19s
kubernetes-bootcamp-5bddb78d8f-c75zp 1/1 Running 0 21s
kubernetes-bootcamp-5bddb78d8f-g5mc7 1/1 Running 0 19s
kubernetes-bootcamp-5bddb78d8f-hlndn 1/1 Running 0 20s
kubernetes-bootcamp-5bddb78d8f-w6s4s 1/1 Running 0 21s
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-56cdd766d-zjx5j 1/1 Terminating 0 29m
kubernetes-bootcamp-5bddb78d8f-7b2jr 1/1 Running 0 35s
kubernetes-bootcamp-5bddb78d8f-c75zp 1/1 Running 0 37s
kubernetes-bootcamp-5bddb78d8f-g5mc7 1/1 Running 0 35s
kubernetes-bootcamp-5bddb78d8f-hlndn 1/1 Running 0 36s
kubernetes-bootcamp-5bddb78d8f-w6s4s 1/1 Running 0 37s
$
我们快速的用kubectl get pods查看pod的情况，发现它先创建了5个新的pod然后逐渐删除旧的pod
应用降级
应用降级很简单，使用undo命令就可以搞定：
$ kubectl rollout undo deployments/kubernetes-bootcamp
deployment.apps "kubernetes-bootcamp"
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-56cdd766d-2j2tp 1/1 Running 0 4s
kubernetes-bootcamp-56cdd766d-gt45v 0/1 Pending 0 2s
kubernetes-bootcamp-56cdd766d-x6wxb 1/1 Running 0 3s
kubernetes-bootcamp-56cdd766d-xwbc6 0/1 ContainerCreating 0 2s
kubernetes-bootcamp-5bddb78d8f-7b2jr 1/1 Terminating 0 4m
kubernetes-bootcamp-5bddb78d8f-c75zp 1/1 Running 0 4m
kubernetes-bootcamp-5bddb78d8f-g5mc7 1/1 Terminating 0 4m
kubernetes-bootcamp-5bddb78d8f-hlndn 1/1 Terminating 0 4m
kubernetes-bootcamp-5bddb78d8f-w6s4s 1/1 Running 0 4m
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
kubernetes-bootcamp-56cdd766d-2j2tp 1/1 Running 0 13s
kubernetes-bootcamp-56cdd766d-gt45v 1/1 Running 0 11s
kubernetes-bootcamp-56cdd766d-kfxcj 1/1 Running 0 8s
kubernetes-bootcamp-56cdd766d-x6wxb 1/1 Running 0 12s
kubernetes-bootcamp-56cdd766d-xwbc6 1/1 Running 0 11s
kubernetes-bootcamp-5bddb78d8f-7b2jr 1/1 Terminating 0 4m
kubernetes-bootcamp-5bddb78d8f-c75zp 1/1 Terminating 0 4m
kubernetes-bootcamp-5bddb78d8f-g5mc7 1/1 Terminating 0 4m
kubernetes-bootcamp-5bddb78d8f-hlndn 1/1 Terminating 0 4m
kubernetes-bootcamp-5bddb78d8f-w6s4s 1/1 Terminating 0 4m
$
看输出结果，同应用升级一样的过程，先创建5个pod，然后逐渐删除旧的pod。
这时候可以用curl来验证一下版本
$ curl minikube:30623
Hello Kubernetes bootcamp! | Running on: kubernetes-bootcamp-56cdd766d-xwbc6 |v=1
看到最后的v=1，说明版本已回退。
4. 总结
kubernetes看起来有点复杂，但想想她用简单的命令完成的操作，比如：应用部署、应用更新，还觉得她复杂吗？我只是觉得：强大！
