Hosting Drupal site in the Amazon EC2 cloud is not difficult. Here is a recipe I have used, first attempt was a Fedora 14 EC2 ami, but Fedora 14 comes with php 5.3, which can't be combined with Drupal 5.x. If you only have Drupal 6 (or Drupal 7) sites to host, you can use Fedora 14. If you want to use a "small" instance, please read this bug about readdir64_r. The fix for that bug is easy:
echo "hwcap 1 nosegneg" > /etc/ld.so.conf.d/libc6-xen.conf
Let's continue with Drupal on CentOS. Rightscale provides perfect CentOS amis that can be used on Amazons EC2 platform. If you install one, these are the steps I took to make it Drupal 5, Drupal 6 and Drupal 7 ready:
# Update the software.
yum -y update
# Set the timezone for this machine.
cp /usr/share/zoneinfo/Europe/Amsterdam /etc/localtime
# This images came with 10Gb of ESB storage, I added another 64 Gb volume, here it's called "/dev/sdc".
# Use LVM to be ready to grow in the future.
vgcreate vg0 /dev/sdc
lvcreate vg0 -L 32G -n var-www
lvcreate vg0 -L 1G -n var-lib-mysql
lvcreate vg0 -L 2G -n root
# Put filesystems on the logical volumes.
mke2fs -j /dev/vg0/var-www
mke2fs -j /dev/vg0/var-lib-mysql
mke2fs -j /dev/vg0/root
# Add the mountpoints to fstab.
echo "/dev/vg0/var-www /var/www/virtualhosts ext3 defaults 0 0" >> /etc/fstab
echo "/dev/vg0/var-lib-mysql /var/lib/mysql ext3 defaults 0 0" >> /etc/fstab
echo "/dev/vg0/root /root ext3 defaults 0 0" >> /etc/fstab
# Create the mountpoints.
mkdir /var/www /var/lib/mysql /root
# Mount all mounpoints in /etc/fstab.
# Install the webserver.
yum -y install httpd
service httpd start
chkconfig httpd on
# Install the database server.
yum -y install mysql-server
service mysqld start
chkconfig mysqld on
/usr/bin/mysqladmin -u root password 'YourPassWord'
# Install PHP and all required Drupal php modules.
yum -y install php php-mysql php-mcrypt php-xml php-mbstring php-gd
# Add a single new file in the ESB root filesystem, that includes configurations from /var/www/conf.d
# Using this trick allows you to easily remount the volume on another host in case of troubles.
echo 'Include /var/www/conf.d/*.conf' >> /etc/httpd/conf.d/virtualhosts.conf
# Rightscale CentOS images comes with postfix and sendmail. Postfix is enabled, but sendmail is fine for me.
# First erase postfix.
yum -y erase postfix
# Now reinstall sendmail to fix a few permissions.
yum -y reinstall sendmail
service sendmail start
chkconfig on sendmail
# Reboot the box to make sure it's working properly.