Pod是Kubernetes最小的管理單元，一個Pod可以代表一個運行在集羣中的進程。
一、創建一個nginx的Pod
使用YAML格式來描述一個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文件中定義了版本，類型，名稱和，鏡像和端口。
創建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>
不僅可以看到pod的啓動狀態，還能看到pod的IP地址（172.30.64.7）和所被分配的節點（k8s-01）。
查看Pod詳情（排錯用）
[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日誌
[root@k8s-01 ~]# kubectl logs pod/nginx-pod
刪除Pod
[root@k8s-01 ~]# kubectl delete nginx-pod
Pod中的鏡像拉取策略 當kubelet嘗試拉取指定的鏡像時，[imagePullPolicy]和鏡像的標籤會生效。
- imagePullPolicy: IfNotPresent：僅當鏡像在本地不存在時鏡像才被拉取。
- imagePullPolicy: Always：每次啓動 pod 的時候都會拉取鏡像。
省略imagePullPolicy，鏡像標籤爲:latest或被省略，Always被應用。 imagePullPolicy被省略，並且鏡像的標籤被指定且不是:latest，IfNotPresent被應用。 imagePullPolicy: Never：鏡像被假設存在於本地。 沒有嘗試拉取鏡像。
二、進入到Pod
怎麼樣進入到Pod中呢？
如果Pod中只有一個容器，可以直接使用下面這個命令：
[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中有多個容器，則需要使用``命令如下：
$ kubectl --namespace=kube-system exec -it nginx-pod -c nginx-app bash
其中ube-system爲namespace名稱，nginx-pod爲pod名稱，nginx-app爲pod中的一個容器的名稱。
三、訪問Pod
從上面的信息中可以看到Pod的ip地址爲172.30.64.7，直接用curl訪問下：
[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>
在集羣中是可以訪問，但是這個nginx部署之後，是給外部提供訪問的，這個時候就要用到kubectl的port-forward了。
可以通過下面這個命令將pod裏面的端口映射到主機上來：
[root@k8s-01 ~]# kubectl port-forward nginx-pod 18080:80
Forwarding from 127.0.0.1:18080 -> 80
可以看到，已經將pod中的80端口映射到了主機的18080端口，現在直接來訪問下：
[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>
這裏只是監聽了127.0.0.1的地址，還可以通過增加--address參數來修改監聽地址，具體可以通過kubectl port-forward --help命令進行查看。