What should I take into consideration while planning a site in Amazon EC2?

Question

Are there any specific requirements for module development and in site architecture for running "heavy" drupal site in several ec2 instances with load balancers?

Answer 1

There isn't anything special within EC2 when compared to other multi server options.

A thing you do need to be aware of is files and how to share/sync your files directory across multiple servers - there are various ways of doing this including CDN, NFS, GlusterFS, cron based rsync. By files I mean the directory specified in /admin/settings/file-system

If you're expecting heavy traffic, then using all the good things like Varnish, APC, Pressflow & memcached are a must (as well as decent monitoring and backups).

There was a pre-configured AMI at one point called Project Mercury, but I'm not sure what the state of that is now.