Q: What are the elements of an AWS CloudFormation template?

AWS CloudFormation templates are JSON or YAML-formatted text files that are comprised of five types of elements:

1. An optional list of template parameters (input values supplied at stack creation time)

2. An optional list of output values (e.g. the complete URL to a web application)

3. An optional list of data tables used to lookup static configuration values (e.g., AMI names)

4. The list of AWS resources and their configuration values

5. A template file format version number

With parameters, you can customize aspects of your template at run time, when the stack is built. For example, the Amazon RDS database size, Amazon EC2 instance types, database and web server port numbers can be passed to AWS CloudFormation when a stack is created. Each parameter can have a default value and description and may be marked as “NoEcho” in order to hide the actual value you enter on the screen and in the AWS CloudFormation event logs. When you create an AWS CloudFormation stack, the AWS Management Console will automatically synthesize and present a pop-up dialog form for you to edit parameter values.

Output values are a very convenient way to present a stack’s key resources (such as the address of an Elastic Load Balancing load balancer or Amazon RDS database) to the user via the AWS Management Console, or the command line tools. You can use simple functions to concatenate string literals and value of attributes associated with the actual AWS resources.