AWS CloudFormation Parameters

Parameters in AWS CloudFormation are inputs that users can provide when they create or update a stack. They are an essential part of making templates reusable and dynamic.

When to Use Parameters

• If a resource configuration is likely to change in the future, make it a parameter.
• If the input value cannot be determined ahead of time, it should be a parameter.

Parameter Settings

• Type: Can be String, Number, CommaDelimitedList, List<Number>, AWS-specific types, or SSM Parameter types.
• Description: A text description of the parameter.
• ConstraintDescription: Describes constraints for the parameter.
• MinLength/MaxLength: Minimum and maximum length for a string parameter.
• MinValue/MaxValue: Minimum and maximum value for a number parameter.
• Default: A default value for the parameter.
• AllowedValues: A list of allowed values for the parameter.
• AllowedPattern: A regex that specifies the allowed pattern.
• NoEcho: If set to true, the parameter value is masked in the output.

Important Parameter Examples

• AllowedValues: Restricts the user to select from predefined options.
  • Example: InstanceType with allowed values t2.micro, t2.small, t2.medium, and default t2.micro.
• NoEcho: Used for sensitive information like passwords to prevent them from being displayed in outputs.

Referencing Parameters

• Use the !Ref function to reference parameters within the template.