502 Bad Gateway Error and How to resolve it

February 22, 2022

There are a lot of errors that can be frustrating and confusing when it comes to WordPress. A popular one is the 502 bad gateway error – but this doesn’t just occur just on WordPress sites; it happens across the web.

What is the Nginx?

Pronounced engine x, Nginx is an open-source web server that is used as a reverse proxy and a load balancer. High-profile companies that use Nginx are Salesforce, Google, Adobe, IBM, etc. Nginx is designed to provide high concurrency while offering low memory usage. Using an event-driven approach, Nginx handles requests in a single thread.

Multiple workers do the actual processing and are controlled by one master process. The request can also be executed by the worker concurrently without blocking other requests because Nginx works asynchronously.

Some of the most common features of Nginx include Reverse proxy caching, load balancing, IPV6, WebSockets, auto-indexing, and FastCGI support with caching.

What is a 502 bad gateway error?

A FastCGI Process Manager for handling web server requests for applications is typically deployed in production behind the Nginx. The Nginx then proxies the web requests to pass them on to worker processes to execute the application. If the proxy is unsuccessful, or if there is no response, then Nginx returns a 502 bad gateway error.

Causes of 502 bad gateway responses

There are three main reasons why a 502 bad gateway can occur. You can consult Nginx’s error log if you don’t find the cause of the error in its access log.

Unresolvable domain name:

Chances are, the domain name is not resolving to any IP or the correct IP. DNS changes take a little more time until they are fully active and propagated. The TTL or time to live controls this as defined for each record.

Server down:

Either the server is down or not reachable. Alternatively, there is no connectivity to the server.

Request blocked by the firewall:

The communication between the server at the origin and the edge server is blocked by a firewall. CMS security plugins may also lead to blockage. Over-reactive DDoS mitigation systems can also block requests from content delivery servers.

Variations and naming conventions of the 502 bad gateway error

  • HTTP Error 502- Bad Gateway
  • 502 Proxy error
  • Blank white screen
  • Error 502
  • HTTP 502
  • 502. That’s an error
  • Error: Server Error – Request could not be completed. Please try after 30 seconds
  • 502 Bad Gateway Nginx

Generally, there is nothing much you can do when this error occurs. At the same time, the error could be temporary as well. You can always give it a second try to fix the issue.

Resolving 502 Errors

Here are certain things that you can do as a user to alleviate the 502 Error:

Page refreshing:

Try refreshing the page. Sometimes the error is only temporary and might just load back. The F5 key works on most browsers to refresh. Alternatively, you can use a ‘refresh’ button from anywhere on the address bar. It just helps to try – but this might not really work.

Check with the others if the site is down:

For whatever reason, if you are unable to reach a site, check if others are also having an issue connecting to the site. If others are having similar troubles, then there are several tools that you could use online to address the issue. Plugin the URL and check for report results. If the site is down for all of them, then you cannot do much except try later. But if the report indicates that the site is working for the others, then the issue must be at your end. This is rather rare in the case of a 502 error, but you can try this too.

Using another browser:

The browser that you are using could have some issues and might be the reason for the 502 error. You might want to check on a different browser. For instance, you can try Safari, Microsoft Edge, or Google Chrome if you have been using something else other than these.

Clearing cookies and cache on the browser:

If another browser is able to put the site up, then the main browser that you are using has outdated cached files that are leading to the error. Remove them and try resolving the issue.

For developers

There are a few reasons why you, as a web developer, might experience a 502 Bad Gateway on the origin server. You might want to try several things, such as checking your fully qualified domain name or FQDN with a DNS Test tool. Alternatively, you may want to run a ping test to verify if the server is reachable. There could be some unusual drops on your firewall error logs.

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