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 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. This is perhaps the biggest source of irritation. While you may know that it could be a server error, there are few details about the underlying issues.

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We’ve broken down what a 503 error is, exactly, as well a how it can manifest, and, crucially, how it can be resolved.

What does HTTP error 503 mean?

While in a handful of cases, a 503 error may refer to a problem with your internet connection or the network being unobtainable, this is more likely to be an error with the server. This means that client requests can’t be fulfilled as they normally would be.

Users who encounter a 503 error may be met with a number of suggested actions, such as ‘retry after’ followed by a certain time window. A handful of websites aren’t even as helpful as this, instead, presenting users with just the fact they’ve encountered such an error. 

What causes a HTTP error 503?

It can be tough to determine the underlying reasons why HTTP 503 errors occur, and they can be encountered for a whole raft of reasons.

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Among the most common issue is a breakdown in communication between the server powering a website and the site itself, leading to the platform’s inability to request resources. As for why this may have happened, these reasons can range from a server being down for maintenance to the hosting company experiencing its own technical problems.

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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.

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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