k8s入门-Pod的基本管理

迷南。 2023-02-12 14:25 20阅读 0赞

Pod是Kubernetes最小的管理单元，一个Pod可以代表一个运行在集群中的进程。

## 一、创建一个nginx的Pod ##

使用YAML格式来描述一个Pod

[root@k8s-01 ~]# cat nginx-pod.yaml 
    apiVersion: v1
    kind: Pod
    metadata:
      name: nginx-pod
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        ports:
        - containerPort: 80

YAML文件中定义了版本，类型，名称和，镜像和端口。

创建Pod

[root@k8s-01 ~]# kubectl create -f nginx-pod.yaml 
    pod/nginx-pod created

查看Pod

[root@k8s-01 ~]# kubectl get pod
    NAME                        READY   STATUS    RESTARTS   AGE
    nginx-pod                   1/1     Running   0          58s

查看Pod更多信息

[root@k8s-01 ~]# kubectl get pod -o wide
    NAME                        READY   STATUS    RESTARTS   AGE   IP              NODE     NOMINATED NODE   READINESS GATES
    nginx-pod                   1/1     Running   0          10m   172.30.64.7     k8s-01   <none>           <none>

不仅可以看到pod的启动状态，还能看到pod的IP地址（172.30.64.7）和所被分配的节点（k8s-01）。

查看Pod详情（排错用）

[root@k8s-01 ~]# kubectl describe pod nginx-pod
    Name:         nginx-pod
    Namespace:    default
    Priority:     0
    Node:         k8s-01/192.168.0.71
    Start Time:   Mon, 11 May 2020 15:00:37 +0800
    Labels:       app=nginx
    Annotations:  <none>
    Status:       Running
    IP:           172.30.64.7
    IPs:
      IP:  172.30.64.7
    Containers:
      nginx:
        Container ID:   docker://db49e7059de1bfbd1b0b1af09625de8e728b12eec7790060a45dfc0cd4db4585
        Image:          nginx
        Image ID:       docker-pullable://nginx@sha256:86ae264c3f4acb99b2dee4d0098c40cb8c46dcf9e1148f05d3a51c4df6758c12
        Port:           80/TCP
        Host Port:      0/TCP
        State:          Running
          Started:      Mon, 11 May 2020 15:01:33 +0800
        Ready:          True
        Restart Count:  0
        Environment:    <none>
        Mounts:
          /var/run/secrets/kubernetes.io/serviceaccount from default-token-4cxn2 (ro)
    Conditions:
      Type              Status
      Initialized       True 
      Ready             True 
      ContainersReady   True 
      PodScheduled      True 
    Volumes:
      default-token-4cxn2:
        Type:        Secret (a volume populated by a Secret)
        SecretName:  default-token-4cxn2
        Optional:    false
    QoS Class:       BestEffort
    Node-Selectors:  <none>
    Tolerations:     node.kubernetes.io/not-ready:NoExecute for 360s
                     node.kubernetes.io/unreachable:NoExecute for 360s
    Events:
      Type    Reason     Age        From               Message
      ----    ------     ----       ----               -------
      Normal  Scheduled  <unknown>  default-scheduler  Successfully assigned default/nginx-pod to k8s-01
      Normal  Pulling    12m        kubelet, k8s-01    Pulling image "nginx"
      Normal  Pulled     11m        kubelet, k8s-01    Successfully pulled image "nginx"
      Normal  Created    11m        kubelet, k8s-01    Created container nginx
      Normal  Started    11m        kubelet, k8s-01    Started container nginx

查看Pod日志

[root@k8s-01 ~]# kubectl logs pod/nginx-pod

删除Pod

[root@k8s-01 ~]# kubectl delete nginx-pod

**Pod中的镜像拉取策略** 当kubelet尝试拉取指定的镜像时，\[imagePullPolicy\]和镜像的标签会生效。

*  imagePullPolicy: IfNotPresent：仅当镜像在本地不存在时镜像才被拉取。
 *  imagePullPolicy: Always：每次启动 pod 的时候都会拉取镜像。

省略imagePullPolicy，镜像标签为:latest或被省略，Always被应用。 imagePullPolicy被省略，并且镜像的标签被指定且不是:latest，IfNotPresent被应用。 imagePullPolicy: Never：镜像被假设存在于本地。 没有尝试拉取镜像。

## 二、进入到Pod ##

怎么样进入到Pod中呢？

如果Pod中只有一个容器，可以直接使用下面这个命令：

[root@k8s-01 ~]# kubectl exec -it nginx-pod bash
    root@nginx-pod:/# ls
    bin  boot  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

如果Pod中有多个容器，则需要使用\`\`命令如下：

$ kubectl --namespace=kube-system exec -it nginx-pod -c nginx-app bash

其中ube-system为namespace名称，nginx-pod为pod名称，nginx-app为pod中的一个容器的名称。

## 三、访问Pod ##

从上面的信息中可以看到Pod的ip地址为`172.30.64.7`，直接用curl访问下：

[root@k8s-01 ~]# curl 172.30.64.7
    <!DOCTYPE html>
    <html>
    <head>
    <title>Welcome to nginx!</title>
    <style>
        body { 
            width: 35em;
            margin: 0 auto;
            font-family: Tahoma, Verdana, Arial, sans-serif;
        }
    </style>
    </head>
    <body>
    <h1>Welcome to nginx!</h1>
    <p>If you see this page, the nginx web server is successfully installed and
    working. Further configuration is required.</p>
    
    <p>For online documentation and support please refer to
    <a href="http://nginx.org/">nginx.org</a>.<br/>
    Commercial support is available at
    <a href="http://nginx.com/">nginx.com</a>.</p>
    
    <p><em>Thank you for using nginx.</em></p>
    </body>
    </html>

在集群中是可以访问，但是这个nginx部署之后，是给外部提供访问的，这个时候就要用到kubectl的`port-forward`了。

可以通过下面这个命令将pod里面的端口映射到主机上来：

[root@k8s-01 ~]# kubectl port-forward nginx-pod 18080:80
    Forwarding from 127.0.0.1:18080 -> 80

可以看到，已经将pod中的80端口映射到了主机的18080端口，现在直接来访问下：

[root@k8s-01 ~]# curl 127.0.0.1:18080 
    <!DOCTYPE html>
    <html>
    <head>
    <title>Welcome to nginx!</title>
    <style>
        body { 
            width: 35em;
            margin: 0 auto;
            font-family: Tahoma, Verdana, Arial, sans-serif;
        }
    </style>
    </head>
    <body>
    <h1>Welcome to nginx!</h1>
    <p>If you see this page, the nginx web server is successfully installed and
    working. Further configuration is required.</p>
    
    <p>For online documentation and support please refer to
    <a href="http://nginx.org/">nginx.org</a>.<br/>
    Commercial support is available at
    <a href="http://nginx.com/">nginx.com</a>.</p>
    
    <p><em>Thank you for using nginx.</em></p>
    </body>
    </html>

这里只是监听了127.0.0.1的地址，还可以通过增加`--address`参数来修改监听地址，具体可以通过`kubectl port-forward --help`命令进行查看。

参考文章：  
[http://k8s.unixhot.com/kubernetes/pod.html][http_k8s.unixhot.com_kubernetes_pod.html]

[http_k8s.unixhot.com_kubernetes_pod.html]: http://k8s.unixhot.com/kubernetes/pod.html