Why Am I Seeing NGINX 502 Bad Gateway: PHP-FPM? (H1)

Maybe you’re already familiar with the feeling of suddenly encountering the infamous NGINX 502 Bad Gateway while comfortably working with PHP-FPM. Right, it is frustrating and quite confusing to see this disruption on your normally functioning web application. But don’t worry; you’re not the only one- this error often leaves both users and developers scratching their heads. In this article, we will help you understand the error in simple terms, delving into its technicalities and exploring how to fix it.

What is NGINX 502 Bad Gateway?

The NGINX 502 Bad Gateway is a rarely occurring error that prevents the user from interacting with a website. Therefore, it becomes crucial for website owners to take this issue as a priority and rectify it. When you see a message similar to “502 Bad Gateway”, it typically means that the server that was acting as a gateway did not receive a valid response from the other server or the upstream server.

How Does NGINX Work With PHP-FPM?

The web requests of various PHP applications are processed through PHP-FPM. TCP/IP socket processes web requests, PHP-FPM works on interpreting the code, while NGINX only handles the HTTP requests. 

It is important to make use of all these services since they individually contribute to enhancing end-user experience. The PHP-FastCGI Process Manager, together with the NGINX proxy server, is capable of increasing the website performance while significantly reducing resource consumption.  

Reasons Behind NPINX 502 Bad Gateway Error and How To Fix Them

Though experiencing an NPINX error could be confusing, there are a few possible reasons why you might be seeing it. 

1. NGINX Is Not Running

One of the top reasons why you could be experiencing the 502 Bad Gateway error could be because NGINX is not up and running. Follow these steps to fix this issue:

• Confirm whether NGINX is operating or not using the command “systemctl status nginx”
• If it’s not working, this command will initiate the display of a message “inactive” or “dead”
• On seeing any of these messages, try restarting NGINX. 

2. PH-FPM Is Not Working

The 502 Bad Gateway can also occur if the NGINX and PHP-FPM are not cooperating. In such a case, you can troubleshoot the issue by following these steps:

• Check if both NGINX and PHP-FPM are correctly configured and functioning properly
• Verify if the location block for PHP scripts is correctly set
• Check the status of PHP-FPM on Linux using the code “ps aux | grep php-fpm”
• This command will display whether PHP-FPM is running or not
• If no PHP-FPM processes are displayed, restart NGINX and PHP-FPM.

3. PHP-FPM Is Timed-Out

You likely see the message “The PHP-FPM timeout has expired” displayed on your screen. This message indicates that PHP-FPM took longer than the required time to execute a certain PHP script. This required time is mentioned in the config file as a timeout value. To resolve this issue, try the following:

• Increase the value of timeout in the PHP-FPM configuration file
• It is best to increase the value of request_terminate_timeout to let scripts run longer
• It is also recommended to investigate why your application is unresponsive
• You may check if your PHP script requires any optimization to improve its execution
• Also, ensure that your server has sufficient resources to execute PHP scripts

4. Requests Blocked by Firewall

One of the major reasons for this error is that the requests get blocked by a firewall. For a 502 Bad Gateway NGINX fix, try the following:

• Check the rules governing firewall to ensure they are not behind blocking requests to NGINX
• Modify the rules according to your firewall solutions to allow inbound traffic to NGINX
• You may also disable the firewall temporarily to check if the 502 error still persists
• Examine the firewall logs to dig out information related to blocked traffic and configure the necessary rules to allow NGINX through it.

5. Domain Name Not Allowed

Quite a few times, the NGINX 502 Bad Gateway error is accompanied by a message stating, “Domain name is not permitted”.  It indicates that NGINX received a request for a domain name that is either not configured or not allowed in the configuration file. Follow these steps to resolve the issue:

• Check the server_name directive to confirm if the domain name is the cause of the error
• Change or add the domain name if it’s incorrect or missing
• Utilise tools like dig or nslookup to verify that the domain name resolves to the correct IP address.

6. Server Unavailable or Bugs in Application

It is possible that the original server is down or there is no connection to it. It leads to the display of a 502 error message on the screen. It is also likely that your web server logs contain loading errors, making the code incompatible with the server configuration and version. In such a scenario, examine the software needs of the application and reconfigure the services accordingly.

Demystify 502 Bad Gateway NGINX Fix with a Webmaster

In the complex world of web development, everything does not always run smoothly. Time and again, you will come across a website greeting you with a “502 Bad Gateway” error instead of some catchy tagline. 

The codes ranging from 500 to 511 indicate that the issue lies with the servers, not the end-user. If a potential customer encounters any kind of error while visiting the website, it could harm the identity of a business and pose a serious blow to its brand value. 

It becomes necessary to stay updated with the best practices of PHP-FPM and NGINX interactions or associate with a team of expert developers like Foreignerds, skilled in minimising such errors and improving the website performance. For a 502 Bad Gateway NGINX fix and more, visit our website to book a  15-minute, no-obligation consultation for free.

FAQs

1. What does the message displayed of the NPINX 502 Bad Gateway mean?

The NPINX 502 Bad Gateway error message indicates that a proxy server is unable to communicate with the upstream server. It could also occur when an upstream server sends no response or a malformed response due to which the NGINX server fails to connect to the backend server. 

2. How do we know that a website is experiencing an NPINX 502 Bad Gateway error?

A message is usually displayed on the screen to inform the user whenever a website encounters this issue. This message can be mentioned as any of the following: “502 Bad Gateway NGINX”, “HTTP 502”, “HTTP Error 502-Bad Gateway”, “502 Service Temporarily Overloaded”, “Temporary Error (502)”, “502 Bad Gateway”, “502 Proxy Error”, or “Error 502”.

3. How important is fixing the NPINX 502 Bad Gateway issue?

The website you developed could need 502 Bad Gateway NGINX fix, failing which will result in a bad user experience. Undoubtedly, websites are now the heartbeat of any business, and an error message can hurt the brand image. Though there is a high chance that 502 errors occurred due to a networking problem, website developers do everything they can to curtail any issues from their end.  

4. Can high web traffic result in an NPINX 502 Bad Gateway error?

Yes, it is possible that high web traffic overwhelms the proxy infrastructure or even the backend servers, resulting in the NPINX 502 Bad Gateway error being displayed. On encountering such a condition, it’s best to either change timeouts, optimize server resources, or make use of load balancers to handle the extra web traffic coming your way efficiently.