About the solution for the inability to access the external network after installing Tomcat on Alibaba Cloud Server Linux

Three issues need to be mentioned here

The first aspect: the problem of starting the firewall on Linux 

The most popular Linux image is CentOS, so the firewall has also become a firewall, so how to operate this firewall?

#停止firewall
systemctl stop firewalld.service 

#开启firewall
systemctl start firewalld.service

#禁止firewall开机启动
systemctl disable firewalld.service 

#查看默认防火墙状态（关闭后显示not running，开启后显示running）
firewall-cmd --state 

But when it is turned on, it may report this error

Failed to start firewalld.service: Unit firewalld.service is masked.

After searching for a long time, I couldn't find a solution, so I tried to enter the following command and solved it.

systemctl unmask firewalld.service

The second aspect: check whether it can be accessed 

Take a look at some commands:

#启动tomcat, 在tomcat目录下（官方名称：apache-****）
bin/startup.sh
#关闭tomcat, 在tomcat目录下（官方名称：apache-****）
bin/shutdown.sh
#如果关闭出错，可以杀死线程
ps -ef | grep tomcat
kill *(端口)
#访问
curl 127.0.0.1:8080
curl ip:8080

The third aspect: external network access problems 

When we use curl ip:8080, we will find that we cannot access it, so what is the problem? 
A: Firewall 
B:. . . 
It was found that the firewall has been closed. After a lot of searching, it was found that it may also be a problem with the security group. After testing, it passed. 
So how to configure the security group? 
1. Log in to Alibaba Cloud 
2. Enter the security group

"Console" -> "Cloud Server ECS" -> select the cloud server -> "More" -> "Security Group Configuration"

3. Configuration rules

"Configure Rules" -> "Add Security Group Rules"

4. Configure port 8080 

Click OK and try again!

Whether you solved it or not, I solved it anyway~