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PHP-FPM configuration

PHP course · Expert · Lesson 44/54

Learn PHP-FPM pool settings and the process manager.

The PHP-FPM pool

PHP-FPM handles requests with worker processes. The pm = dynamic process manager keeps the pool small when idle and grows it under load.

pm.max_children sets the upper bound of concurrent workers. memory_limit is the most memory each worker may consume.

Wrong settings cause 502 Bad Gateway or out-of-memory crashes; pool configuration is critical in production.

Worker counts and memory

A per-worker memory_limit = 128M is enough for typical APIs; heavy job queues need 256M or more.

pm.start_servers is the worker count to start at boot. pm.min_spare_servers and pm.max_spare_servers bound the idle worker range.

Rough guide: pm.max_children × memory_limit must not exceed server RAM. If it does, the OS starts killing processes.

Exercise Generate PHP-FPM pool configuration

Build a PHP-FPM pool config text with PHP: lines pm = dynamic, pm.max_children = 20, pm.start_servers = 4 and memory_limit = 128M. Write it to php-fpm-pool.conf via file_put_contents and echo the text.

Show example solution 
Build $cfg with single-quoted parts joined by "\n". Then call file_put_contents("php-fpm-pool.conf", $cfg); and echo $cfg;.
Example solution:
<?php
// Generate PHP-FPM pool config
$cfg = 'pm = dynamic' . "\n" .
    'pm.max_children = 20' . "\n" .
    'pm.start_servers = 4' . "\n" .
    'memory_limit = 128M' . "\n";
file_put_contents("php-fpm-pool.conf", $cfg);
echo $cfg;

Test yourself

  1. Write the memory_limit value

    <?php
// 128 MB per worker
$cfg = ["memory_limit" => "____"];
print_r($cfg);
    Show answer 
    <?php
// 128 MB per worker
$cfg = ["memory_limit" => "128M"];
print_r($cfg);

  2. Which PHP-FPM setting caps memory per worker?

    • memory_limit
    • pm.max_children
    • max_execution_time
    • upload_max_filesize
    Show answer

    memory_limit — Correct. memory_limit is the most memory each worker may use.

  3. Match the PHP-FPM directives

    pm.max_children
    Maximum worker count
    memory_limit
    Memory per worker
    pm.start_servers
    Workers at startup
    pm = dynamic
    Dynamic process manager

All lessons in Expert

1 Generators

  1. The yield keyword
  2. The Generator class
  3. Memory efficiency
  4. Infinite generators
  5. Delegation with yield from
  6. Pipeline with generators
  7. Summary - Generators

2 Closures and callbacks

  1. The Closure class
  2. Capturing variables with use
  3. Arrow functions (fn)
  4. The callable type
  5. Higher-order functions
  6. Closure binding (bindTo)
  7. Summary - Closures and callbacks

3 Reflection

  1. What is reflection?
  2. ReflectionClass
  3. ReflectionMethod
  4. ReflectionProperty
  5. Reading annotations
  6. Dynamic method invocation
  7. Summary - Reflection

4 Performance

  1. OPcache configuration
  2. Profiling tools
  3. Memory management
  4. Benchmarking
  5. The N+1 query problem
  6. Lazy loading
  7. Summary - Performance

5 Advanced security

  1. password_needs_rehash()
  2. Rate limiting
  3. Security headers (CSP, HSTS)
  4. Session fixation prevention
  5. Input sanitization
  6. Secure file upload
  7. Summary - Advanced security

6 Modern PHP

  1. readonly property
  2. Enums
  3. The match expression
  4. Named arguments
  5. Fibers
  6. First-class callable syntax
  7. Summary - Modern PHP

7 Deployment

  1. PHP with Docker
  2. PHP-FPM configuration
  3. Nginx configuration
  4. CI/CD basics
  5. Environment management
  6. Zero-downtime deployment
  7. Summary - Deployment

8 Expert final

  1. Challenge - Generators and closures
  2. Challenge - Reflection app
  3. Challenge - Performance optimization
  4. Challenge - Secure architecture
  5. Challenge - Full PHP app