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 with a swathe of similar errors, such as the HTTP 502 error, there’s little indication as to what this actually means when you encounter the message. 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.

Not to worry, we’re going to take you through precisely what a 503 error is, including how it is caused and, most importantly, the steps you can take to fix it.

What does HTTP error 503 mean?

A 503 error appears when there is something preventing your browser from accessing the target server – specifically, that the server is unable to handle the request for some reason.

Users are often presented with a handful of suggested actions once an error appears, including trying to access the website after an arbitrary period of time. While this is fairly useless for helping you solve the problem, some websites don’t even offer this advice, instead presenting users with a blank error page.

What causes a HTTP error 503?

Determining the cause of a 503 error can be tough, as they can be caused from a variety of problems, although the fault usually lies with the website’s server, rather than your own system or browser.

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 a 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 is a good time to contact 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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