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What is HTTP error 503 and how do you fix it?

It may not always be obvious what's behind a HTTP error 503, but there are steps you can take to get back online

An HTTP error 503 is found when your browser encounters a website that is unable to establish a connection with its server.

Many people seem to confuse this for the classic 502 bad gateway, but it's a slightly more troubling issue, particularly if you're not an experienced IT professional.

If you're lucky, simply refreshing the page can and should resolve the issue, but there will be times when this easy fix is not enough.

While it might be worth troubleshooting for issues on your own network, in the majority of cases, a 503 error is caused by issues with the web server that the browser is trying to reach. If that is the case, there isn't much one can do aside from reaching out to the IT admin that runs the page, if you even have that information to hand.

What does HTTP error 503 mean?

Essentially, the 503 error is your first warning that something is preventing the browser from accessing the website server. This is where said server is unable to deal with the information requested, though the exact cause won't be made clear at the time. Often you'll just get the annoyingly vague advice to 'try again later'.

​A number of popular sites had 503 issues last year due to the infamous Fastly outage. That included payment sites such as PayPal and Shopify, internet forums like Quora and Reddit, and also streaming giants like Spotify and Twitch. This also affected, as well as numerous online newspapers and news outlets, including the New York Times, BBC, Financial Times, CNN, the Guardian, Bloomberg News, and The Verge, with the latter having to use Google Docs to publish stories.

While many of the websites showed the "503 error", the cloud computing services provider described the issue as a "global CDN disruption", with its own website displaying an "I/O error" message.

What causes an HTTP error 503?

Example of an HTTP 503 error


When met with an HTTP error 503, the first question is usually “why?”, coupled with the hope that determining the cause of the issue will help us solve it quickly and painlessly. Unfortunately, this is not always the case.

Similar to other HTTP errors, determining the root cause of the Error 503 is much harder than one would expect – especially without technical IT expertise. However, there are a few possible scenarios that can be considered as plausible causes for an HTTP error 503.

In the majority of cases, the 503 is triggered when the website in question is no longer able to connect with its supported server, meaning that any information requested or issued by your browser is simply hitting a wall. This usually happens when the server experiences a technical issue, is undergoing maintenance works, or is facing some sort of malicious disruption, such as a denial of service (DDoS) attack. Regardless of the cause, this information will likely not be readily available.

Frequent technical issues, such as those occurring multiple times a month, can be especially disruptive and excessive downtime can cause serious financial difficulty – especially if it heavily depends on online traffic or orders made through e-commerce. Perhaps the best example of this is Amazon's Prime Day disruption in 2018, which should serve as a blueprint for businesses in how not to handle an outage.

Hence, if your website is displaying an HTTP error 503 more often than its own home page, it might be worth switching hosting providers.

Although an HTTP error 503 can diminish the number of customers visiting the site, it can also be caused by an inundation of visitors, such as during seasonal sales. In these cases, the server remains connected, yet is incapable of supporting the avalanche of requests from many different users.

Alternatively, this can also be caused by malicious traffic instead of eager customers, such as in the case of distributed denial of service (DDoS) attacks. Misconfigured web apps may also cause a 503 error to appear, such as a plugin conflict caused by WordPress, while 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.

How to fix an HTTP error 503

As you might know, refreshing the web page is the speediest way to revive the website you’re hoping to access.

What you might not know, however, is there are other measures you can take to ensure the issue isn’t with your computer’s connection. One method is restarting your PC or router. There could be a problem with your hardware configuration if the "Service Unavailable – DNS Failure" error message pops up. This is, reassuringly, easy to fix since you can simply reboot your device. Additionally, choose a different DNS server if you find there’s a problem with the DNS server you’ve been allocated.

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There’s not a lot you can do to fix the issue if the 503 error comes about due to a server side issue. This job lands on the site’s IT administrator who needs to troubleshoot the problem and find a way to fix it since users could be flagging the HTTP 503 errors and get frustrated. Need to apply an update urgently to a site? It’s best to schedule any fixes when the traffic is likely to be fairly low which will ensure web surfers don’t frequently come across problems when visiting your website.

If your site tends to suffer when it experiences surges in traffic, this could mean that you need to invest more in web server resources to prevent the recurring HTTP 503 errors from appearing. Moreover, denial of service (DDoS) attacks can be sometimes responsible for sudden surges of traffic. It might be worth working out how to prevent future attacks by talking to your hosting provider and seeing what mitigations are on offer.

To prevent any more incidents from taking place, it’s also worth investing into more security protections or increasing the frequency you install patches. Protections against DDoS attacks are already offered by a number of hosting providers, which includes only allowing a certain number of users to access your site over a specific period.

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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