Linux – A single php-fastcgi process blocks all other PHP requests

apache-2.2fastcgilinuxmod-fcgidPHP

I've recently switched to a FastCGI setup for PHP (Apache2-worker and mod_fcgid).
However, when a single PHP script is very busy, it seems to block all other PHP requests.
What would be wrong with my configuration?

My main reason for using mod_fcgid is to keep PHP memory usage under control. With mod_php, all individual Apache forks grow in memory after serving PHP.

I've also switched to the apache2-worker model, since there all thread-unsafe PHP code exists outside Apache.

My FastCGI script looks like:

#!/bin/sh
#export PHPRC=/etc/php/fastcgi/
export PHP_FCGI_CHILDREN=5
export PHP_FCGI_MAX_REQUESTS=5000

global_root=/srv/www/vhosts.d/
exec /usr/bin/php-cgi5 \
-d open_basedir=$global_root:/tmp:/usr/share/php5:/var/lib/php5 \
-d disable_functions="exec,shell_exec,system"

My Apache config looks like this:

<IfModule fcgid_module>
  FcgidIPCDir /var/lib/apache2/fcgid/
  FcgidProcessTableFile /var/lib/apache2/fcgid/shm
  FcgidMaxProcessesPerClass 1
  FcgidInitialEnv RAILS_ENV production
  FcgidIOTimeout 600
  AddHandler fcgid-script .fcgi

  FcgidConnectTimeout 20
  MaxRequestLen 16777216

  <FilesMatch "\.php$">
    AddHandler fcgid-script .php
    Options +ExecCGI
    FcgidWrapper /srv/www/cgi-bin/php5-wrapper.sh .php
  </FilesMatch>
  DirectoryIndex index.php
</IfModule>

Best Answer

Found the answer at: https://stackoverflow.com/questions/598444/how-to-share-apc-cache-between-several-php-processes-when-running-under-fastcgi/1094068#1094068

The problem isn't PHP, but mod_fcgid. While PHP spawns multiple children, mod_fcgid is ignorant of it, and will serve one request per child. Hence, when FcgidMaxProcessesPerClass 1 is used, all PHP execution happens after each other. *

The solution presented at which links to: http://www.brandonturner.net/blog/2009/07/fastcgi_with_php_opcode_cache/ explains how to use mod_fastcgi which doesn't have this limitation. It will send multiple requests to the same child.

[*] Note that not using FcgidMaxProcessesPerClass 1 results in many separate instances of PHP, ruby, etc.. while they are all capable of processing many requests internally in a single process.

Hence a new Apache config to use PHP with fastcgi:

<IfModule mod_fastcgi.c>

    # Needed for for suEXEC: FastCgiWrapper On
    FastCgiConfig -idle-timeout 20 -maxClassProcesses 1 -initial-env RAILS_ENV=production
    FastCgiIpcDir /var/lib/apache2/fastcgi

    AddHandler php5-fcgi .php
    Action php5-fcgi /.fcgi-bin/php5-wrapper.sh
    DirectoryIndex index.php

    ScriptAlias /.fcgi-bin/ /srv/www/cgi-bin/
    <Location "/.fcgi-bin/php5-wrapper.sh">
        Order Deny,Allow
        Deny from All
        #Allow from all
        Allow from env=REDIRECT_STATUS
        Options ExecCGI
        SetHandler fastcgi-script
    </Location>

    # Startup PHP directly
    FastCgiServer /srv/www/cgi-bin/php5-wrapper.sh

    # Support dynamic startup
    AddHandler fastcgi-script fcg fcgi fpl
</IfModule>
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