Register a subdomain in amazon ec2 server

Assume that you have a domain of example.com that you have purchase.

1 Find the external IP or DNS for your EC2 instance. You probably want to associate an Elastic IP to your instance, otherwise the IP of your instance will change on reboots.
2 Create a DNS record for your domain, for instance a CNAME record to point to your Elastic IP/DNS name:
subdomain.example.com => ec2-xx-xxx-xxx-xxx.eu-west-1.compute.amazonaws.com
3 Make sure your httpd.conf contains a line to allow virtual hosts:
NameVirtualHost *:80

4 Create a virtual host directive:

httpd.conf:

<VirtualHost *:80>
  ServerName subdomain.example.com
  ServerAdmin webmaster@subdomain.example.com

  DocumentRoot /var/www/example.com/subdomain

  <Directory /var/www/example.com/subdomain>
    Options Indexes FollowSymLinks MultiViews
    AllowOverride All
    Order allow,deny
    allow from all
  </Directory>

  ErrorLog /var/log/apache2/subdomain.example.com.error.log
  LogLevel warn
  CustomLog /var/log/apache2/subdomain.example.com.access.log combined
</VirtualHost>
5 Restart Apache

/etc/init.d/apache2 restart