Troubleshoot 503 errors
Updated
❗
Service Unavailable.
A 503 Service Unavailable on fortrabbit means Apache handed the request to PHP and got no valid answer back. The PHP process ran out of memory, crashed or was overloaded. It often comes together with 504 errors.
What the logs show
A PHP process that dies mid-request writes no PHP error. Look in the Apache error log in the logs instead:
| Code | Meaning |
|---|---|
AH01067 Failed to read FastCGI header | PHP returned no response header: the worker crashed, timed out or was killed |
AH01075 Error dispatching request | The connection to PHP broke off mid-request |
Both point to a PHP process that never finished, not to a problem with Apache.
Common causes
| Cause | Sign | Next step |
|---|---|---|
| Out of memory | OOM kills in the PHP metrics | Out of memory |
| All PHP processes busy | High PHP response time, often also 504 errors | 504 errors, PHP processes |
| A crash in code or an extension | 503 on one page or action only | Turn off plugins or recent code until it stops |
A 503 also appears without any deployment: more traffic, a bot, a bigger database or an editor's action can push the app past its limits. See performance problems are often people problems.
Restart as a workaround
The restart button of the environment restarts Apache and PHP. That frees stuck processes, with a short downtime. The 503 returns when the cause stays.
Platform status
When none of the above fits, check the fortrabbit status page for incidents.