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Error & Status Codes 2 min read

HTTP status code 503 Service Unavailable: causes and solutions

In short

A 503 Service Unavailable means: the website is temporarily unavailable - for example due to maintenance or because too many requests are arriving at the same time. The error is usually limited in time.

What does status code 503 mean?

The server is reachable but cannot process the request at the moment. Unlike 500, this is a temporary state. The server often sends the Retry-After header, which states when the page should be available again.

Typical causes

  • Maintenance mode: the CMS or shop was deliberately put into maintenance mode, for example for updates.
  • Stuck update: WordPress creates the file .maintenance during updates. If the update is interrupted, the file remains and the site permanently shows "Briefly unavailable".
  • Exhausted resources: all available PHP processes are busy - for example due to a rush of visitors, slow pages or many simultaneous bot requests.
  • Server-side maintenance or a brief restart of services.

Solution for visitors

  • Try again after a few minutes.
  • If the page stays unavailable for longer, let the operator know.

Solution for site operators

  • End maintenance mode: deactivate it in your CMS or shop. In WordPress, delete the file .maintenance in the root directory after an interrupted update - via SFTP, file manager or SSH:
rm .maintenance
  • Complete the update: afterwards, check whether all plugins and themes were updated completely and repeat interrupted updates.
  • Reduce the load: page caching, optimised images and slowing down unwanted bots noticeably reduce the number of simultaneous PHP processes. Move long tasks such as imports or newsletters to cron jobs.
  • Absorb peak loads: ShieldCache delivers pages from its Varnish cache and filters out bots and attacks upfront, while our CDN takes over images, scripts and stylesheets. This keeps your website fast and available even during a rush of visitors.
  • Check the error log: reading log files.
  • Regularly at the limit? Then your project needs more headroom - a larger plan or a managed cloud server with dedicated resources. We are happy to advise you.

Tip: 503 for planned maintenance

If you carry out maintenance yourself, 503 is exactly the right status code: search engines recognise the temporary state and keep your pages in the index. Good maintenance plugins automatically send 503 together with Retry-After.

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