anchor.diff:  * RDS Security group: Opens ingress `3306`, and everything for egress.
   
   
  -**Pre-requisites:** The CloudFormation template will require thr following:
  +**Pre-requisites:** The CloudFormation template will require the following:
   
   * A valid VPC
  -* A VPC Internet Gateway configured to access all the touside world
  +* A VPC Internet Gateway configured to access all the outside world
   * Valid subnets for the VPC as described above
   
   **Example:** Given a VPC with a CIDR of `192.168.0.0/16`
  
positive.code: image:https://github.com/killbill/killbill-docs/raw/v3/userguide/assets/aws/cf_stack.png[align=center]
  
  
  The elastic load balancer will listen on the port `80` for routing traffic to our Kill Bill server instances, and on the port `9090` for accessing KAUI, our admin UI. Internally, both Kill Bill server instances, and KAUI server instances will listen on port `8080`.
  
  The CloudFormation template allows to specify different groups of subnets to isolate the Kill Bill server and KAUI server instances with the RDS instances. Typically one would specify at least 2 subnets, in different availability zones for each of those groups. 
  
  The CloudFormation template will also create individual security groups for the various components:
  
  
negative.code: = Installation via CloudFormation
  
  There are at least three different ways to setup a working Kill Bill system on AWS. Two options are based on a single *Amazon Machine Image (AMI)* containing the complete Kill Bill stack, that is both the Kill Bill server and the administrative UI (KAUI). These options are *single tier* and *multitier*. The https://docs.killbill.io/latest//aws-singletier.html[*single tier* option] is designed to deploy a limited version of Kill Bill quickly for trial and experimentation. The https://docs.killbill.io/latest//aws-multitier.html[*multitier* option] is designed for production deployments; this requires more setup than other options,  but provides the most control over the deployment.
  
  A third alternative available for deploying a production system is CloudFormation. This deployment method leverages the capabilites of the AWS infrastructure to provide a robust **production ready** deployment with a single click. Both Kill Bill and KAUI instances can be scaled up or down; CloudWatch provides metrics to follow what is happening; and the RDS database comes automatically configured and ready for use. The entire CloudFormation configuration, or stack, is defined by a *CloudFormation Template*.
  
  == Overview of the Stack
  
  