背景：
三台 centos 虚拟机，部署 hadoop，1 为 namenode，2 和 3 为 datanode
现象描述：
启动 start-dfs 后，检查 jps，1 的 NameNode，SecondaryNameNode 和 DataNode，以及 2,3 的 DataNode 都启动了
在 windows 侧访问 http://spark1:50070，无法访问。
排查步骤：
- 在 1 上检查 50070 端口，netstat -ano |grep 50070，处于监听状态，表示启动正常
tcp 0 0 0.0.0.0:50070 0.0.0.0:* LISTEN off (0.00/0/0)
- 在 1 上通过 curl 访问，返回结果正常
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- 关闭防火墙
service iptables stop
chkconfig iptables off
- windows 上尝试访问，仍然失败，并且能够 ping 通 IP
- 在 DataNode 所在的 2 和 3 虚拟机上 curl 访问，也失败，猜测，防火墙没关闭成功
- 查到 centos7 的防火墙采用 fire-wall，于是检查运行状态
[root@spark1 local]# firewall-cmd --state
running
果然是防火墙的原因，执行关闭命令和开机不启动命令
systemctl stop firewalld.service
systemctl disable firewalld.service
- windows 尝试访问，浏览器正常显示 hadoop 管理界面！
