PHP FPM Configuration: Worker Counts and Memory

FPM capacity depends on per-worker private memory, available RAM and expected concurrent requests.

What It Does and When to Use It

Set parameters in the FPM pool configuration; avoid exposing pool status publicly. The web server handles HTTP, the PHP worker executes scripts, and CLI has separate configuration and lifecycle.

Requirements, Inputs and Expected Behavior

Confirm the runtime, extension, environment variables, and permissions before running the examples in production. Sizing max_children from average RSS alone can oversubscribe memory during peaks.

Example 1: Basic Operation

Set parameters in the FPM pool configuration; avoid exposing pool status publicly.

pm = dynamic
pm.max_children = 12
pm.start_servers = 3
pm.min_spare_servers = 2
pm.max_spare_servers = 6

Example 2: Behavior and Validation

Run the matching status or validation command on the intended host.

php-fpm8.4 -tt

Practical Example: Application Use

Correlate capacity, worker crashes and slow requests using logs and process state.

sudo systemctl status php8.4-fpm --no-pager
sudo journalctl -u php8.4-fpm -n 35 --no-pager

Important Behavior and Edge Cases

The second example highlights: Run the matching status or validation command on the intended host. The practical example adds: Correlate capacity, worker crashes and slow requests using logs and process state.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• FPM capacity depends on per-worker private memory, available RAM and expected concurrent requests.
• Correlate capacity, worker crashes and slow requests using logs and process state.
• Check the effective configuration in the SAPI serving requests before changing production.