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

HTTP error 503 service unavailable

One of the most frustrating error messages as both a developer and as an internet user is the "503" error message when trying to access a website.

The reason it's so frustrating? Like many other "50-" errors, it will give little indication as to what's gone wrong. Sure, you may know its a server error, but what exactly is causing the problem?

We explain what a 503 error is, how it can present itself and how it can be fixed if it's causing you headaches and stunting your productivity.

What does HTTP error 503 mean?

Although in some cases a 503 error usually refers to an internet connection problem, with the network being unobtainable, it's most commonly a problem on the server-side, meaning client requests can't be fulfilled as expected.

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You may see a suggested action, such as "retry after..." in the header message, along with a suggested time frame for retrying to access the site, or it may not even be that helpful.

What causes a HTTP error 503?

HTTP 503 errors can occur for a multitude of reasons, and it can be difficult to determine the root cause in many of these cases.

One of the most common issues behind a 503 error is a communication breakdown between the server and the website, resulting in a site’s inability to request resources. This can happen for a number of different reasons, such as a server being down for maintenance or if the hosting company is experiencing its own technical difficulties. In the latter example, you may find that some companies are more prone to failure than others, so it’s always worth considering switching providers to find the best one for your operations.

A 503 error may also display if the server lacks sufficient capacity to support the number of users attempting to access a website. This often happens when a website with a typically lower volume of regular visitors experiences a sudden spike in traffic, whether that’s due to a page becoming incredibly popular or because it has been targetted by 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.

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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.

If sites visitors are reporting HTTP 503 errors on a regular basis, then the administrator needs to troubleshoot the issue and find the appropriate fix.

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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.

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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.

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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