kubeadm join 命令无法加入node节点，ip_forward 内核参数没有被正确设置

在kubeadm init后，使用给出的命令加入node节点

遇到问题：

[preflight] Running pre-flight checks
	[WARNING IsDockerSystemdCheck]: detected "cgroupfs" as the Docker cgroup driver. The recommended driver is "systemd". Please follow the guide at https://kubernetes.io/docs/setup/cri/
	[WARNING SystemVerification]: this Docker version is not on the list of validated versions: 26.1.4. Latest validated version: 19.03
	[WARNING Hostname]: hostname "k8s-node2" could not be reached
	[WARNING Hostname]: hostname "k8s-node2": lookup k8s-node2 on 114.114.114.114:53: no such host
error execution phase preflight: [preflight] Some fatal errors occurred:
	[ERROR FileContent--proc-sys-net-ipv4-ip_forward]: /proc/sys/net/ipv4/ip_forward contents are not set to 1
[preflight] If you know what you are doing, you can make a check non-fatal with `--ignore-preflight-errors=...`
To see the stack trace of this error execute with --v=5 or higher

最关键的错误是：

[ERROR FileContent--proc-sys-net-ipv4-ip_forward]: /proc/sys/net/ipv4/ip_forward contents are not set to 1

这个错误表示 ip_forward 参数的值不是 1。ip_forward 允许系统充当路由器，将数据包从一个网络接口转发到另一个，这对于 Kubernetes 中 Pod 之间的跨节点通信至关重要

解决这个问题，需要编辑 /etc/sysctl.d/kubernetes.conf 文件（如果不存在就新建一个）。

1. 编辑配置文件:

   vi /etc/sysctl.d/kubernetes.conf
   

2. 添加以下内容:

   net.ipv4.ip_forward = 1
   

3. 使配置生效:

   sysctl --system
   

完成上述步骤后，重新运行 kubeadm join 命令，应该就能成功将节点加入集群了