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

The derided 503 error message is one of the most frustrating issues you can encounter when trying to visit a web page. 

Like other HTTP errors, such as the 502 bad gateway error, it's not easy to figure out what's causing the issue, and as a general user, the error number is just about as helpful as the broken website you're struggling to access.

That said, there are a few steps you can take to rectify the issue. Keep in mind, though, it’s possible the issue lies with the web server the browser is trying to access, so your attempts may not always be successful.

What does HTTP error 503 mean?

A 503 error means something is preventing the browser from accessing the target website's server. Typically, this means the server has been unable to handle the information request, but the cause of this won't necessarily be obvious.

This error usually comes with a handful of suggested fixes to remedy the situation. Unfortunately, one of those repairs is just to try and access the website later. Sure, this advice is frustrating and useless, but it's better than displaying a blank error page, which is what some websites do.

What causes an HTTP error 503?

Example of an HTTP 503 error

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 quickest way of attempting to resolve this issue is by refreshing the web page and crossing your fingers that it’s enough to resurrect the site you’re trying to access.

There are a few other steps you can take, however, to ensure the problem isn’t related to your connection. You can, for example, restart your computer or router. Should an error message show “Service Unavailable – DNS Failure”, this normally means there could be an error with the configuration of your hardware, which is usually corrected by performing a reboot. If there’s a problem with the allocated DNS server, it’s usually resolved by simply choosing another DNS server to use.

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If, however, the 503 error comes as a result of something that’s at fault on the server’s side, then there's not a whole lot you can do yourself. The IT administrator for a site will need to troubleshoot the issue and find a solution to the problem that users are reporting if they’re routinely being met with HTTP 503 errors. Should you be in that position, and you realise that updates need to be applied to a site, it’s best to schedule them when traffic is likely to be lowest so users don’t regularly encounter errors.

Traffic spikes may also cause an HTTP 503 error, and if these happen on a regular basis, it's best to take this as a sign that you need to increase your investment in web server resources. Relatedly, a surge of traffic may be the result of a denial of service (DoS) attack, in which case it would be wise to approach your hosting provider to enquire about the possible mitigations they may be able to offer to prevent future attacks.

Further investing in security protections or increasing the frequency of patch management could also serve to prevent any incidents from occurring in future. Several providers already include DDoS protection as part of their default packages, which may restrict the number of users that are allowed to access a site at any one time.

Finally, should the HTTP 503 error be a result of a programming bug, you’ll need to undergo further investigation to pinpoint the issue and rectify it permanently.

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