What is a 503 Service Unavailable Error?

This article explains what a 503 error means, why you’re getting an HTTP 503 code, and how to troubleshoot these errors.

What is an HTTP 503 Error?

When you open a web page, your browser sends a request to the server hosting the site, which returns the requested data and response code. The HTTP response status code is returned by the server and tells the client whether the request has been successful or not.

Respons codes are categorized into five classes. The codes in the 500 to 599 range are indicating a server error.

The HTTP status code 503 is a generic error response returned when the server cannot handle the request. There are many reasons why a server is not ready to complete the request and return a 503 error. This error code usually appears when the server is overloaded with requests or down for maintenance.

If the page you are visiting throws 503 Error, there is nothing much you can do since your browser or Internet connection does not cause the error. Even though the error is on the server-side, you can try some of the following options:

• Reload your browser or try opening the page with another one. The chances that the page will load when you refresh your browser are low, but still, it’s worth giving it a try.
• Try to clear your browser cache. If the page that shows a 503 error is cached, the browser will request a new version of the page after the cache is cleared.
• Come back later. The webmaster may fix the webserver issue in the meantime.
• Contact the website owners. The last remaining option is to get in touch with the person responsible for maintaining the website.

Troubleshooting 500 Error

Several different reasons could cause the 503 Internal Server Error. The most common are the following:

• Distributed Denial of service (DDoS) attack. A DDoS attack is an attempt by a malicious party to flood the bandwidth or resources of your system and overload it. When the system gets overloaded, it is not able to serve the requests.
• Automated Maintenance. You may not know it, but your server may go through regular service or software maintenance. For example, if you have a WordPress site, it is automatically updated to the latest version whenever there’s a new release. During the update process, WordPress returns a 503 Service Unavailable error.
• Firewall settings. Often a misconfigured firewall can cause a 503 error. This usually happens when the application is using a content delivery network (CDN). The server firewall may recognize the requests from the CDN as an attack and block them, resulting in a 503 error.

• Hacked site. A malicious code that is injected into your website may result in a 503 error.
• Issues with plugins and themes. If you are running WordPress or similar CMS, the 503 error can appear after updating or modifying a plugin/theme.
• Node.js server. If you have Node.js based site, check if the Node.js server crashed or just not running.

The best way to determine why the 503 error occurred is to check the server log files. The location of the log files depends on your Linux distribution and the webserver. The most common locations for Apache and Nginx are as follows:

/var/log/apache2/error.log
/var/log/httpd/error_log
/var/log/nginx/error_log

If your application is built on Node.js, check the Node.js logs.

Typically, the server log contains detailed information about the error that will help you identify and fix the error.

Conclusion

The 503 Internal Server Error is an HTTP status code meaning that something went wrong with the web server hosting the site you’re visiting.