PHP-FPM

Also Known As

TL;DR

Explanation

PHP-FPM (FastCGI Process Manager) runs PHP as a separate service communicating with the web server (typically Nginx) via FastCGI. It manages a pool of PHP worker processes, restarting crashed workers, and supports dynamic/static/ondemand process management strategies. Key configuration includes pm.max_children (limits concurrency and memory), request_terminate_timeout (prevents runaway processes), and slowlog (identifies slow scripts). Unlike Apache mod_php, PHP-FPM isolates PHP execution from the web server, improving security and allowing different pools per virtual host.

Diagram

flowchart TD
    REQ[HTTP Request] --> NGINX[nginx]
    NGINX -->|FastCGI| MASTER[PHP-FPM Master]
    MASTER --> W1[Worker 1<br/>handling request]
    MASTER --> W2[Worker 2<br/>idle]
    MASTER --> W3[Worker 3<br/>idle]
    W1 --> OPCACHE[OPcache<br/>compiled bytecode]
    W1 --> DB[(Database)]
    W1 --> REDIS[(Redis)]
    INFO[Each worker handles one request<br/>pm.max_children = concurrency limit]
style MASTER fill:#6e40c9,color:#fff
style W1 fill:#238636,color:#fff
style OPCACHE fill:#1f6feb,color:#fff
style INFO fill:#d29922,color:#fff

Common Misconception

Why It Matters

Common Mistakes

• Using the default pm = dynamic settings without tuning for your application's memory per worker.
• Setting pm.max_children too high — workers exceed available RAM and the server starts swapping.
• Not setting request_terminate_timeout — runaway scripts hold workers indefinitely, starving new requests.
• Not monitoring the PHP-FPM slow log — slow requests are invisible without it.

Code Examples

# php-fpm pool.conf — untuned defaults:
pm = dynamic
pm.max_children = 50        ; Too high if each worker uses 100MB — that's 5GB RAM
pm.start_servers = 5
pm.min_spare_servers = 5
pm.max_spare_servers = 35
; request_terminate_timeout = 0 — infinite by default, runaway scripts block workers

; /etc/php/8.3/fpm/pool.d/www.conf
[www]
user  = www-data
group = www-data
pm                   = dynamic
pm.max_children      = 50     ; workers x memory < available RAM
pm.start_servers     = 5
pm.min_spare_servers = 2
pm.max_spare_servers = 10
pm.max_requests      = 500    ; recycle to prevent memory leaks

request_slowlog_timeout = 5s
slowlog = /var/log/php-fpm/slow.log
pm.status_path = /fpm-status

chdir = /var/www/app
php_admin_value[open_basedir] = /var/www/app:/tmp
php_admin_value[disable_functions] = exec,system,shell_exec

References

• ↗ https://www.php.net/manual/en/install.fpm.php
• ↗ https://www.php.net/manual/en/install.fpm.configuration.php

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