This is part 2 of the setup, where we concentrate on making the server production ready. Part 1 focus on the basic server setup to get Drupal running, you can find Part 1 here.
Performance
Opcode cache helps speed up your PHP considerably. We are using APC here, there are other alternatives such as XCache, eAccelerator, Zend Optimizer, etc.
Install APC Opcode
This will install APC 3.0.18-1
# aptitude install php-apc
Restart Apache for APC to take effect