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！