HTTP Error Codes and Solutions: A Guide to 502 Bad Gateway and Other Common Server Errors

Your website may be returning a "502 Bad Gateway" or similar error to visitors. These types of HTTP status codes indicate an issue between the client (browser) and the server. When CDN (content delivery network) services like Medianova are used, this error is detailed as shown in the image: the browser and CDN are working, but the main server (host) is returning an error. In this article, we cover all HTTP error codes and their solutions in detail.

❌ What is 502 Bad Gateway?

Meaning: The gateway or proxy server did not receive a valid response from the origin server.

Possible Reasons:

The server may have crashed
The web server (Apache, Nginx) is not running
PHP-FPM, Node.js, MySQL services may have stopped
DNS configuration error
The firewall may be blocking CDN servers
The backend cannot respond due to excessive traffic

✅ Solution Suggestions:

Restart your web server (Apache/Nginx)
Check PHP-FPM or related application services
Monitor whether there is enough RAM/CPU on the server
Make sure you have configured DNS records correctly
If you are using a CDN like Cloudflare/Medianova, remove IP blocks

Other Common HTTP Error Codes and Meanings

Code	Description	Possible Reasons	Solution
400	Bad Request	Invalid request	Check URL characters
401	Unauthorized	No authorization	API Token / Login information must be added
403	Forbidden	Access denied	IP/role block, directory permissions
404	Not Found	Page not found	Check URL, see if file exists
405	Method Not Allowed	Incorrect method such as POST instead of GET	API endpoint check
408	Request Timeout	Server did not respond within the expected time	Performance optimization
429	Too Many Requests	Too many requests sent	Rate limit is applied, wait
500	Internal Server Error	Unknown error on the server side	Check error logs (error.log)
501	Not Implemented	Server cannot handle the request	Update/compatibility issue
502	Bad Gateway	CDN or proxy cannot get a response from the backend server	Web server check
503	Service Unavailable	Server is under maintenance or overloaded	Check scheduler / Insufficient RAM
504	Gateway Timeout	CDN or proxy server timed out	PHP script may take too long

Monitoring and Testing Tools

curl -I https://yourwebsiteaddress.com → Check HTTP response
ping, traceroute → Is there a network access problem?
journalctl -xe (Linux) → Examine service logs
CDN logs (Medianova, Cloudflare) → Is there a response delay or blocking?

✅ Conclusion

HTTP error codes are important diagnostic tools for system administrators and developers. The 502 Bad Gateway error usually indicates a temporary problem on the server side. In CDNs like Medianova, the cause of this error is clearly shown: the browser and CDN are working, but the main server is not responding. With the table and suggestions above, you can recognize other error codes and quickly produce solutions.