Understanding Status Codes
Behind every error page you see on the web there is an HTTP status code sent by the web server. Status codes come in the format of 3 digit numbers. The first digit marks the class of the status code:
1XX status codes have informational purposes
2XX indicates success
3XX is for redirection
None of these three classes result in an HTML error page as in this cases the client knows what to do and goes on with the task without hesitation. What we usually see are the 4XX and 5XX kind:
4XX represent client-side errors
5XXs indicate problems on the server side
HTML error pages are displayed in these cases because the client has no idea about what how to move on. Let’s see what happens in the background when something goes south and what you can do about it.
Server Errors (5XX)
7. 500 – Internal Server Error
Internal Server Error is the most well-known server error, as it’s used whenever the server encounters an unexpected condition that prevents it from fulfilling the client’s request. The 500 error code is a generic one, it’s returned when no other server-side 5XX error codes make any sense.
500
Although in this case the problem is not on your end, you can do some things to resolve it such as reload the page (as the error may be temporary), clear your browser’s cache (as the issue may occur with the cached version of the site), and delete your browser’s cookies and restart the browser.
You can also contact the webmaster (like in case of any other server-side problems) – they may be grateful for your contribution but there’s also a chance that they are aware of the problem and already working on it.
If you encounter the 500 error page on your own site, it will be wise to contact your hosting provider. The reason is most likely a permission error, a corrupt .htaccess file or a too low memory limit. If you have a WordPress site, the 500 error can also caused by a third party plugin; you can test this by deactivating your plugins, one by one, until the culprit is found.
8. 502 – Bad Gateway
The 502 error message represents a communication problem between two servers. It occurs when the client connects to a server acting as a gateway or a proxy that needs to access an upstream server that provides additional service to it. The other server is located higher in the server hierarchy. It can be for example an Apache web server that’s accessed by a proxy server, or the name server of a large internet service provider that’s accessed by a local name server.
When you encounter the Bad Gateway error page the server receives an invalid response from an upstream server.
502
In most cases it doesn’t mean that the upstream server is down but that the two communicating servers don’t agree on the protocol about how to exchange data. This usually happens when one of the machines is incorrectly configured or programmed. Contact your hosting provider if you see 502 on your own site.
9. 503 – Service Temporarily Unavailable
You see the Service Temporarily Unavailable (sometimes Out of Resources) message any time there’s a temporary overload on the server, or when it’s going through a scheduled maintenance. The 503 error code means that the web server is currently not available. This is usually a temporary condition that will be resolved after some delay.
503
If you are a website owner it’s important to have appropriate knowledge about the 503 status code to properly handle scheduled maintenance. If you don’t handle scheduled maintenance in the correct way, you may hurt the search engine ranking of your site.
Learn how to do this via this tutorial on Yoast’s SEO blog or this one on moz.com.
10. 504 – Gateway Time-Out
There is a server-server communication problem behind the Gateway Time-Out error message, just like behind the 502 Bad Gateway error code. When the 504 status code is returned there’s also a higher-level server in the background that is supposed to send data to the server that is connected to our client. In this case the lower-level server doesn’t receive a timely response from the upstream server it accessed.
This is the same time-out problem that occurs in case of the 408 Request Time-Out status code, but here it doesn’t happen between the client and the server but between two servers in the back end. The Gateway Time-Out error page usually indicates slow communication between the two servers, and it can also happen that the higher-level server is completely down.
504
As 504 is a network problem in the background only people who have access to that network can solve it. As with other server-side HTTP errors, sometimes it’s enough to refresh the page a few minutes later to tackle the issue – of course only if the service providers work on the problem meanwhile.
