I am setting up a Drupal website that might have critical traffic for a while. What is the best setup (distro, apache/ngynx/lighttpd, reverse proxy, sql server, php version, etc) to handle it?
Drupal configurations/modules are welcome, as well.
Given the majority of users will be anonymous, I would highly recommend Pressflow and Varnish
Here is a list of high profile / traffic Drupal sites using Pressflow. If you do some benchmarking before and after implementing varnish you'll be very happy with the increase in req/sec.
Here are a couple resources:
To summarize: use APC and Memcached, try to limit the number of Drupal modules you use and be judicious with your logging (e.g. use syslog to write Drupal events to a file instead of to the Database).