Error 503 often occurs intermittently. To monitor your website and receive availability information by email or other channels, consider the Add-on Service EWM ⧉.
If you are experiencing frequent Error 503 occurrences on hosting with WordPress, also see the article Webhosting - WordPress.
This article covers:
Error 503: Service temporarily unavailable
You can recognize Error 503 by the large heading Service Temporarily Unavailable at the top of the page. Below it, you will find an English error description and a link to this article.
With Error 503 Service Temporarily Unavailable can occur on any website that uses PHP or similar technologies. The server is running at full capacity, yet it does not respond to new requests. The problems are usually caused by reaching the limits of certain Webhosting parameters.
Resolving Error 503
Every Webhosting NoLimit ⧉ has up to 25 PHP processes reserved on our server (7 for LowCost ⧉, 30 for Extra ⧉), which can run simultaneously. This means the processor can handle at most that many PHP requests at once. Requests that take too long to process are queued and wait for their turn. If no PHP process becomes available within the specified period (the timeout), they return Error 503.
Under normal circumstances, 25 PHP processes are sufficient – with a properly optimized website, you will not encounter this problem.
The most common causes of Error 503 are:
- an ongoing attack on the web server,
- poor website or database optimization,
- insufficient service resources,
- stuck PHP process.
Attack on the web server
A common cause of Error 503 is an attack or another form of request flooding that exhausts processes and blocks real visitors’ access. In this situation, the error usually occurs intermittently and lasts a few to tens of minutes.
You can detect this by enabling logging using the guide Webhosting – Logging, enabling both Accesslog and Errorlog.
- In Access log lists website accesses, including specific addresses. Nonsensical addresses or parameters (after ? in the address) are a common sign of an attack.
- In Error log shows when Error 503 occurred. If these times match suspicious traffic spikes in Accesslog, the error was probably caused by an attack.
WEDOS offers effective attack protection through WEDOS Protection ⧉. If attacks frequently cause Error 503, consider deploying this protection.
Website and database optimization
If the website is not optimized, even normal traffic or inefficient use of external resources or the database can overwhelm it. The error occurs intermittently, during traffic peaks or automatic maintenance, and lasts a few to tens of minutes.
Common causes of Error 503 and their solutions include:
- An improperly optimized PHP application: The application does not send requests to the processor efficiently. If you use a CMS, check whether it supports caching. If so, enable it. This significantly reduces script execution time and SQL database queries, speeding up your website. For more information, see the article Webhosting – Cache and Proxy.
- Overly frequent or long-running background processes: Maintenance scripts, especially those uploading or downloading data, can occupy many processes for a long time, leaving none for ordinary visitors. For regular maintenance, we recommend configuring Webhosting CRON. Schedule backups and other resource-intensive processes outside peak hours.
- A large number of database records: The application stores visitor access logs or similarly large datasets in the database. Consider which data you really need and adjust the application or hosting accordingly.
- Unsuitable database configuration: The application has poorly configured database tables. PHP then waits a very long time for the results of SQL queries.
- The PHP application connects to an unavailable external resource: The application downloads external data, but the destination server cannot be reached, does not respond or is overloaded. If this happens frequently, consider changing the external data source.
- A cron script runs too long: Many cron jobs or long-running jobs can block the PHP processes available to your website. Consider which jobs the application actually needs, how often, and how to optimize them.
- File downloads handled through a PHP script: The application uses a PHP script to download large files, occupying a PHP process throughout the download. Instead, link or redirect directly to the file URL.
- Many files in an unsuitable directory structure: The application has more than thousands of items in a single directory. Organize files into suitable directories.
Error 503 may therefore be unrelated to current traffic or website changes. Common causes include loading data from a slow or unavailable external source, or a cron job that spends a long time loading, updating or maintaining data. Several complex requests may also coincide by chance, typically searches in large databases.
Increasing service resources
If you cannot find a way to optimize the website, adjust service resources to its requirements. Consider these options:
- Changing the Webhosting plan: You can upgrade Webhosting from LowCost to NoLimit or from NoLimit to Extra. Compare plan resources at this link ⧉. For instructions on changing plans, see the article Services – Changing the Plan or Billing Period.
- Changing the service: If shared Webhosting resources are insufficient for your application but you want to retain Customer Administration management, consider moving the application to WMS ⧉.
- Separating aliases and subdomains. Aliases and subdomains share Webhosting resources. If traffic on one or more aliases or subdomains causes Error 503, consider separate hosting for that domain or subdomain.
Stuck PHP process
Rarely, Error 503 may also be caused by a stuck PHP process. If Error 503 persists for tens of minutes to hours and clearing the cache does not help (e.g. using Ctrl+Shift+R), restart PHP on your hosting.
During PHP version changes, temporary incompatibility with the selected version may cause website PHP errors.
Follow these steps:
- Log in to Customer Administration ⧉.
- In the top menu, select Hosting services Webhosting.
- Select the Webhosting whose PHP you want to restart.
- In the left menu, select PHP configuration.
- Change to another PHP version, preferably the closest one (e.g. PHP 7.4 7.3, or 8.0 8.1).
- Click the button Edit.
- Wait half an hour for the PHP version change to take effect. Then restore the original version in the same way.
If Error 503 persists after this restart, its cause is probably something other than a stuck process.
Frequently asked questions
Is Error 503 specific to WEDOS servers?
Error 503 can occur on any web server. When choosing hosting for your application, first understand its requirements and select a service accordingly. Besides file and database storage, pay attention to RAM and CPU parameters. Remember that higher performance also affects the service price.
Does 503 mean WEDOS.protection is blocking me?
No. Protection displays a fallback page when the website does not respond in time. If unsure, send us ⧉ the date, time and Req-ID from the error page. We will locate the specific request and why it failed.
Will upgrading the plan resolve the error?
Upgrading helps partly because a higher plan has more PHP processes. However, it does not remove the cause: a task running for thirty seconds still occupies a process, even on a higher plan, and several such tasks can leave no processes for normal traffic. We recommend doing both.
How do I resolve Error 503 in WordPress?
In WordPress, overly demanding background processes are a common cause. For more information and troubleshooting steps, see the article Webhosting - WordPress.
I disabled the entire website but still see Error 503. Why?
Try clearing the browser cache (e.g. with Ctrl+Shift+R). If that does not help, restart PHP using the procedure in the section Stuck PHP process.