在Pod中配置主机网络（hostNetwork）

配置说明

Pod使用主机网络只需要在配置中添加hostNetwork: true即可。

1. 请参见通过kubectl连接集群，使用kubectl连接集群。
2. 创建YAML文件host-network.yaml，示例如下：

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: nginx
   spec:
     replicas: 1
     selector:
       matchLabels:
         app: nginx
     template:
       metadata:
         labels:
           app: nginx
       spec:
         hostNetwork: true
         containers:
         - image: nginx:alpine
           name: nginx
         imagePullSecrets:
         - name: default-secret

3. 执行以下命令，创建一个使用主机网络的Pod。

   kubectl apply -f host-network.yaml

4. 部署后可以看到Pod的IP与节点的IP相同，说明Pod直接使用了主机网络。

   kubectl get pod -owide

   输出如下：

   NAME                    READY   STATUS    RESTARTS   AGE     IP          NODE        NOMINATED NODE   READINESS GATES
   nginx-6fdf99c8b-6wwft   1/1     Running   0          3m41s   10.1.0.55   10.1.0.55   <none>           <none>

hostNetwork使用注意事项

Pod直接使用主机的网络会占用宿主机的端口，Pod的IP就是宿主机的IP，使用时需要考虑是否与主机上的端口冲突，因此一般情况下除非某个特定应用必须占用宿主机上的特定端口，否则不建议使用主机网络。

由于Pod使用主机网络，访问Pod需要直接通过节点端口，因此要注意放通节点安全组端口，否则会出现访问不通的情况。

另外由于占用主机端口，使用Deployment部署hostNetwork类型Pod时，要注意Pod的副本数不要超过节点数量，否则会导致一个节点上调度了多个Pod，Pod启动时端口冲突无法创建。例如上面例子中的nginx，如果服务数为2，并部署在只有1个节点的集群上，就会有一个Pod无法创建，查询Pod日志会发现是由于端口占用导致nginx无法启动。

请避免在同一个节点上调度多个使用主机网络的Pod，否则在创建ClusterIP类型的Service访问Pod时，会出现访问ClusterIP不通的情况。

该问题定位步骤如下：

1. 查看工作负载状态。

   kubectl get deploy

   回显如下，存在1个Pod无法启动。

   NAME    READY   UP-TO-DATE   AVAILABLE   AGE
   nginx   1/2     2            1           67m

2. 查看Pod状态。

   kubectl get pod

   回显中Pod存在CrashLoopBackOff状态。

   NAME                    READY   STATUS             RESTARTS   AGE
   nginx-6fdf99c8b-6wwft   1/1     Running            0          67m
   nginx-6fdf99c8b-rglm7   0/1     CrashLoopBackOff   13         44m

3. 查看该Pod的日志。

   kubectl logs nginx-6fdf99c8b-rglm7

   日志中存在端口已被占用的信息：bind() to 0.0.0.0:80 failed (98: Address in use)

   /docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration
   /docker-entrypoint.sh: Looking for shell scripts in /docker-entrypoint.d/
   /docker-entrypoint.sh: Launching /docker-entrypoint.d/10-listen-on-ipv6-by-default.sh
   10-listen-on-ipv6-by-default.sh: info: Getting the checksum of /etc/nginx/conf.d/default.conf
   10-listen-on-ipv6-by-default.sh: info: Enabled listen on IPv6 in /etc/nginx/conf.d/default.conf
   /docker-entrypoint.sh: Launching /docker-entrypoint.d/20-envsubst-on-templates.sh
   /docker-entrypoint.sh: Launching /docker-entrypoint.d/30-tune-worker-processes.sh
   /docker-entrypoint.sh: Configuration complete; ready for start up
   2022/05/11 07:18:11 [emerg] 1#1: bind() to 0.0.0.0:80 failed (98: Address in use)
   nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address in use)
   2022/05/11 07:18:11 [emerg] 1#1: bind() to [::]:80 failed (98: Address in use)
   nginx: [emerg] bind() to [::]:80 failed (98: Address in use)
   2022/05/11 07:18:11 [emerg] 1#1: bind() to 0.0.0.0:80 failed (98: Address in use)
   nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address in use)
   2022/05/11 07:18:11 [emerg] 1#1: bind() to [::]:80 failed (98: Address in use)
   nginx: [emerg] bind() to [::]:80 failed (98: Address in use)
   2022/05/11 07:18:11 [emerg] 1#1: bind() to 0.0.0.0:80 failed (98: Address in use)
   nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address in use)
   2022/05/11 07:18:11 [emerg] 1#1: bind() to [::]:80 failed (98: Address in use)
   nginx: [emerg] bind() to [::]:80 failed (98: Address in use)
   2022/05/11 07:18:11 [emerg] 1#1: bind() to 0.0.0.0:80 failed (98: Address in use)
   nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address in use)
   2022/05/11 07:18:11 [emerg] 1#1: bind() to [::]:80 failed (98: Address in use)
   nginx: [emerg] bind() to [::]:80 failed (98: Address in use)
   2022/05/11 07:18:11 [emerg] 1#1: bind() to 0.0.0.0:80 failed (98: Address in use)
   nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address in use)
   2022/05/11 07:18:11 [emerg] 1#1: bind() to [::]:80 failed (98: Address in use)
   nginx: [emerg] bind() to [::]:80 failed (98: Address in use)
   2022/05/11 07:18:11 [emerg] 1#1: still could not bind()
   nginx: [emerg] still could not bind()