What should I do if PHP cannot open the internal network when opening the external network?

There is a problem that has troubled many PHP developers recently, that is, the intranet can be accessed from the external network, but cannot be accessed from the internal network. This problem can be tricky, but it's not that difficult to solve.

First of all, we need to understand the cause of this problem. When we access the external network from the internal network, we usually access it through NAT conversion. NAT conversion will not only map the external network IP to the internal network, but also map the requested port. However, when accessing the internal network from the external network, because the IP of the internal network is a private IP, it cannot be directly accessed by the external network. Therefore, we need to perform a reverse proxy to allow the external network to access the internal network.

Let’s take a look at how to solve this problem. Suppose our external network domain name is "www.example.com" and the internal network IP is "192.168.1.100", then we can solve this problem by deploying a reverse proxy service on the external network. This can be achieved by using common reverse proxy servers like Nginx or Apache.

On Nginx, we can implement reverse proxy by editing the Nginx configuration file. First, add the following code to the Nginx configuration file:

server {
    listen 80;
    server_name www.example.com;

    location / {
        proxy_pass http://192.168.1.100:80;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }
}

The function of this code is to proxy all access requests to "www.example.com" to the IP in the intranet. Among them, the proxy_pass parameter specifies the IP address and port number in the intranet. proxy_set_header Parameters are used to set some header information to make the code more accurate when proxying. For specific information, please refer to Nginx official documentation.

On Apache, we can use the mod_proxy module to implement reverse proxy. First, you need to enable the mod_proxy module in httpd.conf:

LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_http_module modules/mod_proxy_http.so

Then, add the following code in the configuration file:

<VirtualHost *:80>
    ServerName www.example.com
    
    ProxyRequests Off
    ProxyPass / http://192.168.1.100:80/
    ProxyPassReverse / http://192.168.1.100:80/
    ErrorLog logs/reverse-proxy-error.log
    CustomLog logs/reverse-proxy-access.log common
</VirtualHost>

The function of this code is to remove all pairs of "www.example. com" access requests are proxied to the IP in the intranet. Among them, ProxyPass specifies the IP address and port number in the intranet, and ErrorLog and CustomLog are used to set the paths of the error log and access log respectively. For specific information, please refer to Apache official documentation.

To summarize, to solve the problem that PHP cannot be opened on the external network and cannot be opened on the internal network, you need to deploy a reverse proxy service on the external network. By configuring a reverse proxy, we can proxy all external network requests to the internal network, thereby realizing communication between the internal network and the external network.

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