k8s入门-Pod的基本管理

程序员文章站 2024-03-11 19:22:01

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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

[[email protected]-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

[[email protected] ~]# kubectl create -f nginx-pod.yaml 
pod/nginx-pod created

查看Pod

[[email protected] ~]# kubectl get pod
NAME                        READY   STATUS    RESTARTS   AGE
nginx-pod                   1/1     Running   0          58s

查看Pod更多信息

[[email protected] ~]# 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）

[[email protected] ~]# 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://[email protected]: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

[[email protected] ~]# kubectl logs pod/nginx-pod

删除Pod

[[email protected] ~]# 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：

[[email protected] ~]# kubectl exec -it nginx-pod bash
[email protected]:/# 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：

[[email protected] ~]# 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：

[[email protected] ~]# 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：

[[email protected] ~]# 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>