Example of troubleshooting method to solve Nginx port conflict

Problem Description

A Spring + Angular project with separated front-end and back-end, using Nginx for data forwarding.

Nginx listens on port 8100, front-end port 4200, and back-end port 8080.

As usual, configure MySQL and Redis in advance, import the project's Nginx configuration file, and then start the frontend and backend successfully.

Then a problem arose: only a very small number of requests initiated by the front-end could be received by the back-end, and most of them were 404. As I clicked on the browser, 404 kept appearing in the console.

If it's just 404, then the problem is very simple, it's very likely that the Nginx port forwarding settings are wrong. But the magic of it is that there are still a few requests that can reach the background.

(In the above picture, when the save is successful, the background does output relevant console information)

Other friends did not have this problem, so I started to investigate.

Troubleshooting process

In order to figure out whether it is a backend problem or an Nginx forwarding problem, you need to first check from the browser's Network whether the 404 is returned by the backend or by Nginx.

After checking, I found that it was returned by Nginx. If the background returns 404, the error information will be written in the HTTP request header.

First check whether there is any conflict in the listening port. Use nginx -T to view the complete Nginx configuration file, including the imported external files.

// Test whether the configuration file is correct and output the complete configuration file nginx -T 

In the output results, only 8100 is seen, indicating that although multiple projects have been introduced, there is no listening port conflict.

Then I plan to look for some clues from the Nginx log.

After turning on Nginx's log mode, I checked the log files and found thousands of access records.

Most are 404s, a few are 200s, but the logs don't provide much useful information.

Finally, the problem was found in the configuration file:

For Nginx installed using HomeBrew, the default listening port in its global configuration file is 8080, and the port occupied by the project backend is also 8080.

Although I don't know much about the principles of port monitoring and port occupation, at least I know that since Nginx monitors port 8080, some requests are sent to Nginx itself, and the other part is sent to the background.

Therefore, modify the global configuration file, change the default port, and the problem will be solved.

// Modify the configuration file sudo vim /usr/local/etc/nginx/nginx.conf
// Test configuration file nginx -t
// Restart Nginx
nginx -s reload

Finally, all requests can reach the backend.

Summarize

When I first started learning XAMPP, I often heard: "If there is a conflict with port 80, change the port, for example, change it to 8080."

But when 8080 becomes our habit, some projects will also use this port...so we need to solve the conflict problem.

When changing the default port in the future, it is recommended to change it to a port that is unlikely to be used, such as a port number above 10000, to avoid conflicts with the project's port.

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