HTTP 503 (Service Un­avail­able): meaning and troubleshoot­ing

The HTTP Error 503 is one of the most popular error messages on the World Wide Web. This status code has already been en­countered by nearly every internet user. In some cases, all you have to do is re-load the page, but this doesn’t always work: It requires more than simply re­fresh­ing the browser window a couple of times to make the 503 error message disappear.

It doesn’t matter whether you’re using a desktop, tablet, or smart­phone, the 503 status code is the server’s way of informing visitors that the service they’re trying to reach isn’t available (Service Un­avail­able). This article explains what causes the error message to be shown and what solutions are available for users and server operators.

The Error Code 503 is one of several status codes that a server can use to respond to HTTP requests from clients, such as web browsers. By doing this, it informs the client whether the request has been suc­cess­fully processed or whether further steps are needed from the client’s side to complete the pro­cessing. 503 is one of the HTTP codes that informs of any server-side error, which would prevent the request from being processed. The message sent would then be 'Service Un­avail­able', which informs the client that the server is tem­por­ar­ily not available. A cor­res­pond­ing value in the 'Retry-After' field in the header of the HTTP response can be used to specify that at a later time the request is able to be processed.

The error message’s exact wording can vary slightly, as the following list of some of the common variants shows:

• Status code HTTP Error 503
• HTTP 503
• HTTP Error 503
• HTTP Error 503 The service is un­avail­able
• 503 Error
• HTTP Server Error 503
• Error 503 Service Un­avail­able
• HTTP /1.1 Service Un­avail­able
• 503 Service Un­avail­able Error
• 503 Service Tem­por­ar­ily Un­avail­able
• Service Un­avail­able – DNS Failure
• Error 503 Maximum threads for service reached

The 503 Error is both annoying for visitors as well as for web project operators. It’s es­pe­cially prob­lem­at­ic if the user needs to use the service quickly, but the site can’t be accessed: for example, if you want to make a bank trans­ac­tion or send an e-mail. Also, users who rely on web apps or cloud services such as browser games, Office solutions, storage platforms, or project tools, don’t want to have to wait for the web presence to be available again.

The operators re­spons­ible for the re­spect­ive web project should look into troubleshoot­ing. On the one hand, the in­ac­cess­ib­il­ity of the service in­ev­it­ably leads to dis­sat­is­fied users and traffic loss; on the other hand, if HTTP 503 error messages occur too fre­quently, they can lead to a decreased search engine ranking.

If you want to access a web project via the browser and end up receiving the 503 status code, you’re not usually told what the exact reason is. An exception (as mentioned earlier) is main­ten­ance work, which is planned by the website operator and is therefore usually indicated by a cus­tom­ised 503 Error page. This page often provides in­form­a­tion on how long the site will be in­ac­cess­ible for. If there is no in­dic­a­tion that the HTTP 503 Error is the result of main­ten­ance, you can try to solve the

'Service Un­avail­able' problem with the following tricks.

It is possible that the server was unable to answer the HTTP request correctly. In this case, it may be enough to just refresh the page to resolve the HTTP 503 error. To do this, simply click on the refresh button next to your browser’s address bar or al­tern­at­ively use the [F5] key or the [Ctrl] + [R] key com­bin­a­tion.

It has already been suggested that the cause of a 503 error can be due to a problem with the DNS server. In most cases, this is indicated by the specific message 'Service Un­avail­able – DNS Failure', which indicates a faulty DNS con­fig­ur­a­tion of the system or the router, as well as showing that there’s a technical problem with the selected DNS server. While you can solve the former scenario by re­start­ing your device, the latter problem can be more ef­fect­ively helped by selecting another DNS server.

If you took the ini­ti­at­ive and still weren’t suc­cess­ful after the refresh attempts, re­start­ing, and con­fig­ur­ing the DNS server, it’s best to close the page and try again later. Since the cause of the in­ac­cess­ib­il­ity is often too much traffic, you will be de­creas­ing the burden on the server by closing the page. By trying again later, the server will have hopefully sta­bil­ised and will be able to process all HTTP requests as desired. The same applies, of course, when the 503 Error pages are due to main­ten­ance, but the operator is not informed about this by a specific error page.

If a website is un­avail­able for an extended time, it may be useful to contact the ap­pro­pri­ate ad­min­is­trat­or or support, if it’s available. This may help you learn about the reasons behind the HTTP 503 issue and the current state of troubleshoot­ing.

As a website operator, it is in your own interest to fix HTTP 503 Errors as quickly as possible or even try to stop them from happening at all. Otherwise this leads to dis­sat­is­fied users, loss of traffic, and being penalised by search engine machines.

It isn’t always possible to prevent errors from happening. For example, if your server is tem­por­ar­ily shut down because of main­ten­ance work being done on your project. However, with ap­peal­ingly designed error pages, you have the op­por­tun­ity to inform your visitors about the cir­cum­stances sur­round­ing the downtime. In addition, it is useful to specify a time when your site will be available again once you’re able to estimate the duration of the main­ten­ance. Further tips and tricks for dealing with Error Code 503 can be found in the following para­graphs:

Traffic is probably the biggest issue when it comes to the HTTP 503 problem. On the one hand, one of the most important goals is to attract as many visitors as possible, but on the other hand, the increase in visitors causes an overload of the server and therefore increases the prob­ab­il­ity of 503 errors. It is therefore very important to maintain an overview of the user numbers and to increase hosting resources in good time to ensure long-term stability. If you are running web projects that are heavily dependent on seasonal events, such as online shops for Christmas shopping, you should choose a hosting solution that allows for a temporary increase in server capacity.

If malicious software and spam are trig­ger­ing the 503 errors, you should im­me­di­ately contact your hosting provider and work with them to resolve the issue. To avoid scenarios like these, you should pay close attention to your web project’s security right from the get go. The con­di­tions of your provider play an important role – how much pro­tec­tion you receive depends on the chosen server package. For example, you should always use up-to-date software and import available updates as soon as possible. Otherwise, outdated ap­plic­a­tions with known vul­ner­ab­il­it­ies will quickly become a gateway for hackers.

Another cause of an HTTP 503 Error generated by the server could be that the web project or the content man­age­ment software is in­cor­rectly pro­grammed. For example, WordPress is very vul­ner­able to 503 errors due to loading times being too long. This can result from an excessive number of database access attempts or badly pro­grammed plugins, which make the CMS perform ad­di­tion­al functions, but often slow down the process at the same time. The same applies if you integrate too many ex­ten­sions. The solution is to filter out the prob­lem­at­ic plugins so that you can de­ac­tiv­ate them if you need to.