What is HTTP error 503 and how do you fix it?

It may not always be obvious what's causing the issue, but there are steps you can take to get back online

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The derided 503 error message is possibly one of the most frustrating errors to encounter when trying to access a website, not just as a developer but as a general user.

As is the case with most other HTTP errors, including the 502 bad gateway error, there’s no way for you to tell precisely what has gone wrong. Unless you’re au fait with website development, it’s likely that the error number is as helpful to you as the broken website you’re trying to access.

However, there are some steps you can take to try and fix the issue, although it’s possible the problem is with the web server the browser is trying to access.

What does HTTP error 503 mean?

A 503 error displays when something has prevented a browser from accessing the server of a target website – typically that the server has been unable to handle the information request, although the reason for this won’t be obvious.

The error is normally accompanied by a handful of suggested actions to help remedy the situation, although one of these will be to simply try and access the website at a later time. While this advice can be frustrating, and useless for helping you solve the problem, some sites simply display a blank error page.

What causes a HTTP error 503?

As is the case with the 502 bad gateway error, diagnosing the cause of a 503 error is difficult. Usually, it’s the case that something has gone wrong with the server supporting the website you’re trying to access.

The most common cause of the 503 error is a breakdown in communication between the server and the website it is supporting, resulting in that website being unable to handle any information requests from a user’s browser. This could have been due to scheduled server maintenance or by some unforeseen technical issue. If the latter, you might find that some websites are down more regularly than others, normally a sign that their hosting provider is inadequate.

A 503 error may also occur if the server is still online but lacks sufficient capacity to support the number of requests hitting a website. This often happens when a website that normally sees low traffic is suddenly hit with an influx of new users. This spike in traffic can be from users flocking to the site, such as when a promotional deal is running, however, it’s most often the case that these spikes are caused by malicious traffic, such as a distributed denial of service (DDoS) attack.

Misconfigured web apps may also cause a 503 error to appear, such as a plugin conflict caused by WordPress.

Regular 503 errors could suggest an issue with the domain name system (DNS), whether that’s an incorrect server configuration or an issue with the DNS server itself.

Figuring out precisely what’s gone wrong is important for ultimately getting a site back online.

How to fix an HTTP error 503

The easiest solution is to refresh the page and see if that can bring it back.

You can also attempt to restart your computer or router. If the error message shows "Service Unavailable – DNS Failure", there may be a fault with the DNS configuration of the computer or the router. A router problem can be fixed by restarting it. In the case of a problem with a selected DNS server, it may be fixed by choosing another DNS server to use.

Unfortunately, if the 503 error is the result of a server-side issue, there’s nothing much you can do as a site visitor to fix the problem.

If a site’s visitors are reporting HTTP 503 errors on a regular basis, then the administrator needs to troubleshoot the issue and find the appropriate fix. If there are updates needed for a website, schedule these at a quieter time so that users don't see this message regularly.

If spikes in traffic are causing the error, then it may well be time to increase web server resources to cope with the increase in visitors.

If the error is caused by a denial of service (DoS) attack, it's worth contacting a hosting provider to see what mitigations can be put in place to avoid this happening again. You may want to look at increasing security or applying patches that hackers may use to attack your website and take it offline. Many hosting providers have DDoS protection in place, which can limit the number of users being funnelled to a site at any given time.

Lastly, if the error is due to a programming error, further investigation will be required to pinpoint the issue and take steps to correct it.

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