[Summary] Common reasons and solutions for PHP reverse proxy inaccessibility

When using a reverse proxy, you may encounter inaccessibility problems. Especially when using PHP as a reverse proxy, this problem seems to be more prominent. This article explains common causes and solutions to this problem.

1. Caching issues

When using a reverse proxy, the connection between the backend server and the client is intercepted by the proxy server. If the proxy server has a local cache, it will immediately return the cached content without getting the actual content. As a result, the requested URL is not correctly passed to the backend server, resulting in normal access.

Solution:

Clear the cache of the proxy server, or use a new proxy server.

2. DNS resolution issues

Sometimes, inaccessibility issues may be caused by DNS resolution failure. When you visit a URL, your browser first needs to resolve the URL to an IP address before it can access the website at that IP address. If DNS resolution fails, then you cannot access the URL.

Solution:

Make sure that the DNS configuration is correct and that the DNS server can be accessed normally.

3. HTTPS/SSL certificate issue

If you use HTTPS/SSL, a certificate error may occur during the reverse proxy. This is usually caused by incorrectly configured certificates between the proxy server and the backend server.

Solution:

1) Make sure your certificate is issued by a trusted third-party organization.

2) Check the certificate configuration between the proxy server and the backend server.

3) If you use a self-signed certificate, make sure your browser trusts the certificate.

4. Apache server issues

If you use Apache server as a proxy server, you will encounter some problems when reverse proxying. One of the most common problems is not handling the Content-Length header correctly.

Workaround:

Use Nginx or another server as a proxy server, or modify the Apache configuration to handle the Content-Length header.

In short, if you encounter inaccessible problems when using PHP for reverse proxy, be sure to eliminate the above common causes first. If none of the above solutions work, it's likely that the cause is some deeper server configuration issue, and you'll need to carefully examine the various configuration and log files to find the problem.

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