title: use one common public ip address for multiple ec2 instances
body: <p>I'm using aws ec2 instances as web servers. </p>
  
  <p>There are more then 20 web servers and they has to connect to some external services. Those external services has ip based security rules. Because of this reason I have to use a only one or two public ip address to connect those services. </p>
  
  <p>How can i route outgoing traffics to use only one public ip address ?</p>