Diagnosing and Resolving PHP-FPM High CPU Usage Print

Welcome back to Serverhacks—a collection of tips, tricks, and troubleshooting guides for servers, networking, and system administration. I’m Corels from Emmanuel Corels Creatives, and in today’s article, we’re tackling a common challenge for web administrators: high CPU usage in PHP-FPM. When PHP-FPM (FastCGI Process Manager) consumes excessive CPU resources, your web applications can slow down or become unresponsive. In this guide, I’ll walk you through a systematic approach to diagnose the root cause of high CPU usage in PHP-FPM and implement effective solutions.

Step 1: Verify the Symptoms

Before diving into detailed diagnostics, it’s important to confirm that PHP-FPM is indeed the culprit.

• Check CPU Usage:
  On your server, use tools like top or htop:

  top -o %CPU
  

  Look for PHP-FPM processes (often listed as php-fpm or similar) consuming a high percentage of CPU.

• Identify Spike Patterns:
  Note whether the CPU usage spikes during specific times or when certain pages are requested. This can help narrow down whether the issue is related to a particular application or configuration.

Step 2: Review PHP-FPM Configuration

Misconfigurations in PHP-FPM can lead to inefficient resource usage.

• Examine the Pool Configuration:
  PHP-FPM’s pool configuration files are typically located in /etc/php/7.x/fpm/pool.d/ (replace 7.x with your PHP version). Open the relevant pool file, for example:

  sudo nano /etc/php/7.4/fpm/pool.d/www.conf
  

  Check key parameters:

  • pm.max_children: This setting determines the maximum number of child processes. If set too high, it can overwhelm the CPU.
  • pm.start_servers, pm.min_spare_servers, pm.max_spare_servers: These control the number of processes that start and remain idle. Over-provisioning here can also lead to high CPU usage.

  Tip: Consider lowering pm.max_children if your server hardware is limited, or tuning the spare server settings based on your typical load.

• Log Slow Requests:
  Enable slow log in PHP-FPM to capture scripts that take too long to execute:

  request_slowlog_timeout = 5s
  slowlog = /var/log/php7.4-fpm.slow.log
  

  This will help you identify which PHP scripts are causing bottlenecks.

Step 3: Monitor and Analyze Logs

Logs provide invaluable insights into what’s happening under the hood.

• PHP-FPM Error Log:
  Check the PHP-FPM error log for any warnings or errors that might indicate a problem:

  sudo tail -n 50 /var/log/php7.4-fpm.log
  

• Slow Log Analysis:
  Review the slow log file you configured. Look for frequently occurring slow scripts and assess whether they can be optimized.

  sudo tail -n 50 /var/log/php7.4-fpm.slow.log
  

• Web Server Logs:
  Also check your web server’s logs (e.g., Apache or Nginx). High CPU usage in PHP-FPM can sometimes correlate with specific HTTP requests that are resource-intensive.

Step 4: Test Application Performance

Identify if specific application code is responsible for high CPU usage.

• Profile PHP Scripts:
  Use tools like Xdebug or Blackfire to profile the performance of your PHP applications. These tools can pinpoint inefficient functions or database queries.

• Benchmark and Stress Test:
  Tools like Apache Benchmark (ab) or JMeter can simulate traffic to help identify how your PHP-FPM configuration performs under load:

  ab -n 1000 -c 10 http://yourdomain.com/some_script.php
  

Step 5: Adjust and Optimize

Based on your findings, implement the following adjustments:

• Tune PHP-FPM Settings:

  • Reduce pm.max_children to a value that matches your server’s capabilities.
  • Adjust spare server settings (pm.min_spare_servers and pm.max_spare_servers) to better match your typical traffic.

• Optimize Application Code:

  • Refactor inefficient PHP scripts.
  • Optimize database queries that might be causing long execution times.

• Implement Caching:
  Consider using an opcode cache like APCu or OPcache, and an HTTP accelerator (e.g., Varnish) to reduce the load on PHP-FPM by serving cached responses.

• Hardware Considerations:
  If the CPU is consistently overburdened despite optimizations, consider upgrading your server resources or distributing the load across multiple servers.

Step 6: Monitor Post-Optimization

After applying your changes, continuously monitor the performance:

• Use top and htop Regularly:
  Monitor CPU usage to see if the adjustments have stabilized resource consumption.
• Log Analysis:
  Continue reviewing error logs and slow logs to ensure no new issues have emerged.
• Feedback Loop:
  Regularly gather feedback from users regarding performance improvements and iterate on your configuration as needed.

Final Thoughts

High CPU usage in PHP-FPM can be caused by a variety of factors—from configuration settings and inefficient application code to external traffic spikes. By following a systematic approach—verifying system resources, reviewing configuration files, analyzing logs, testing application performance, and applying targeted optimizations—you can significantly improve the performance of your PHP-FPM processes.

I hope this guide helps you troubleshoot and resolve high CPU usage issues effectively. Remember, the key is to iteratively monitor and adjust your setup based on real-world usage. If you have any questions or need further assistance, feel free to reach out. Happy troubleshooting, and here’s to a faster, more efficient server environment!

Explained with clarity by
Corels – Admin, Emmanuel Corels Creatives