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 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 fastest method to resurrect the site you're trying to access is by refreshing the web page and hoping that this will solve the problem.

However, there are also several other steps you can take to make sure the problem isn't linked to your connection. For example, you can restart your router or computer. If an error message shows "Service Unavailable – DNS Failure", then this usually means there may be an error with your hardware configuration, which thankfully can be corrected by performing a reboot. You might find there is a problem with the allocated DNS server, but this is normally resolved by choosing to use a different DNS server.

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However, if the 503 error is a result of a problem found on the server's side, then unfortunately there isn't a lot you can do yourself to remedy it. This is where the IT administrator for the site should troubleshoot the issue to find a solution to the fault that users are reporting if they are encountering HTTP 503 errors. If you find yourself in that position and discover that updates need to be applied to a site, it's recommended to schedule them when your site's traffic is likely to be lowest, so your users don't regularly come across errors.

Alternatively, HTTP 503 errors can also be caused by traffic spikes, and if these occur regularly, it's best to use this as a sign that you might want to increase your web server resources investment. In addition to this, a surge of traffic could be the result of a denial of service (DoS) attack, in which case it might be a clever idea to approach your hosting provider to ask about the possible mitigations they can offer you to prevent attacks in the future.

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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