CloudFormation Parameters¶

• Parameters are a way to provide inputs to your AWS CloudFormation template
• They're important to know about if:
  • You want to reuse your templates across the company
  • Some inputs can not be determined ahead of time
• Parameters are extremely powerful, controlled, and can prevent errors from happening in your template thanks to types.

When should you use a parameter?¶

• Ask yourself this:
  • Is this cloudformation resource configuration likely to change in the future?
  • If so, make it a parameter
• You won't have to re-upload a template to change it's content

Parameters:
    SecurityGroupDescription:
        Description: Security Group Description
        Type: String

Parameter Settings¶

Parameters can be controlled by all these settings.

• Type
  • String
  • Number
  • CommaDelimitedList
  • List
  • AWS Parameter (to help catch invalid values - match against existing values in the AWS Account)
• Description
• Constraints
• ConstraintDescription (String)
• Min/MaxLength
• Min/MaxValue
• Defaults
• AllowedValues (array)
• AllowedPattern (regexp)
• NoEcho (boolean)

How to Reference a Parameter¶

• The Fn::Ref function can be leveraged to reference parameters
• Parameters can be used anywhere in a template
• The shorthand for this in YAML is !Ref
• The function can also reference other elements within the template

DbSubnet1:
    Type:: AWS::EC2::Subnet
    Properties:
        VpcId: !Ref MyVPC

Pseudo Parameters¶

• AWS offers us pseudo parameters in any CloudFormation template
• These can be used at any time and are enabled by default