VPS Performance tuning and scaling - Linux VPS

Please note that the following guide might not be applicable for those using newer versions of CentOS and Debian, which might be making use of PHP fcgi, PHP fpm, nginx etc.

So you've bought a CentOS VPS from us and you find that sometimes you run out of memory and things go wrong.

We've got a few tips and tricks for you to help keep your VPS ticking over.

Adjusting the number of web based clients your VPS can handle from 1 second to the other.

   1. First you should backup the file with the following command

          cp /etc/httpd/conf.d/swtune.conf /etc/httpd/conf.d/swtune.backup.`date  +%F-%H-%M`

   2. The following command opens swtune.conf

          vi /etc/httpd/conf.d/swtune.conf (this command requires that you have some knowledge of using vi, the command nano may be easier to use)

      you should see the following section marked "prefork MPM".

Note: The file on a Debian VPS is located at /etc/apache2/apache2.conf

   3. Edit the section that reads:

          <IfModule prefork.c>
          StartServers       2
          MinSpareServers    1
          MaxSpareServers    5
          MaxClients         10
          MaxRequestsPerChild  1000
          </IfModule>

      to something more like this (changes marked in bold):
          * For VPS Stater:

            <IfModule prefork.c>
            StartServers       1
            MinSpareServers    1
            MaxSpareServers    3
            MaxClients         50
            MaxRequestsPerChild  1000
            </IfModule>

    4. Save this file by first hitting the Esc key and then typing :wq [hit enter]

    5. Restart apache

     /etc/init.d/httpd restart [hit enter]

The timeout settings in Apache can sometimes cause problems and keep your visitors waiting for content.

   1. First you should backup the file with the following command

          cp /etc/httpd/conf.d/swtune.conf /etc/httpd/conf.d/swtune.backup.`date  +%F-%H-%M` [hit enter]

   2. The following command opens swtune.conf

          vi /etc/httpd/conf.d/swtune.conf [hit enter] [this command requires that you have some knowledge of using vi, the command nano may be easier to use)

   3. Use the following keystrokes to find "Timeout"

      /Timeout [hit enter]

   4. Edit the section that reads:

    Timeout 120
       
    to a more reasonable value like the following (changes marked in bold):

    Timeout 20   

   5. Save this file

   6. Restart Apache to apply the changes:

    /etc/init.d/httpd restart [hit enter]

A note from the author:

To find out if the MaxClients setting is causing you grief, it's easiest to login to your VPS and run:

    grep -i maxclient /var/log/httpd/error_log

This command should give you some details if this setting has been reached.