The error Resource temporarily unavailable: AH03104: ap_thread_create: unable to create worker thread in the Apache logs indicates that the system is unable to spawn new threads, typically due to insufficient resources. This can happen either within a Docker container or on the host system if Apache is running as a system service.
Example log entries:
[Fri Jun 27 12:07:37.418582 2025] [mpm_event:alert] [pid 1175:tid 1176] (11)Resource temporarily unavailable: AH03104: ap_thread_create: unable to create worker thread
[Fri Jun 27 12:07:39.424369 2025] [mpm_event:alert] [pid 1194:tid 1195] (11)Resource temporarily unavailable: AH03104: ap_thread_create: unable to create worker thread
[Fri Jun 27 12:07:41.426793 2025] [mpm_event:alert] [pid 1213:tid 1214] (11)Resource temporarily unavailable: AH03104: ap_thread_create: unable to create worker thread
[Fri Jun 27 12:07:42.827692 2025] [proxy_fcgi:error] [pid 8:tid 13] (70007)The timeout specified has expired: [client 172.18.0.4:51626] AH01075: Error dispatching request to : (polling)
If Apache is running in a Docker container, check the container’s resource usage with:
docker stats --no-stream apacheExample output:
This will show if the container is hitting resource limits (memory, CPU, PIDs, etc.). If so, increase the allocated resources (e.g., memory or PID limit), then restart the Apache container or service:
systemctl restart apache2
OR
docker restart apacheIf Apache is running directly on the host system, monitor system-level resource usage using tools like:
top
htop
free -m
ulimit -a
Make sure there’s enough free memory, and consider increasing the maximum number of processes or threads if needed.
