AWS CloudFormation Concepts Intrinsic Functions

External

Intrinsic Function Reference

Internal

• AWS CloudFormation Concepts

Overview

All intrinsic functions have full function name:

Fn::ImportValue: stack_output_export_name

and a short form:

!ImportValue stack_output_export_name

Ref

Ref

The intrinsic function Ref returns the value of the object it refers to, such as a parameter or resource. When a parameter logical name is specified, it returns the value of the parameter. When a resource logical name is specified, it returns a value that can be typically used to refer to that resource, such as a physical ID.

!Ref AWS::StackName
!Ref MyParameter
!Ref MyResourceName

GetAtt

GetAtt

An intrinsic function that returns arbitrary attributes of a resource (Ref returns just important value associated with the resource). The function takes two parameters: the logical name of the resource and the attribute to be retrieved, as an array.

Using GetAtt to Configure the ARN of a Resource Created by the Template

Resources:

  # this resource has an ARN
  AccessLogGroup:
    ...

  ...
  
  # this resource needs the ARN
  Stage:
    Type: AWS::ApiGateway::Stage
    Properties:
      ...
      AccessLogSetting:
        DestinationArn: !GetAtt AccessLogGroup.Arn
        ...

Join

Join

The Fn::Join function takes two parameters, a delimiter that separates the values you want to concatenate and an array of values in the order that you want them to appear.

!Join [ delimiter, [ comma-delimited list of values ] ]

!Join ['-', [ a, b, c ]]

!Join ['-', !Split ['/', !Sub '${something}-something-else']]

returns "a:b:c"

Split

Split

!Split ['.', "www.example.com"]

!Split ['/', !Sub '${something}-something-else']

returns ["www", "example", "com"].

Select

Select

ImportValue

ImportValue

The Fn::ImportValue returns the value of an output exported by another stack. The function is used to create cross-stack references.

Can be used as a key in a YAML structure:

...
ServiceRole:
  Fn::ImportValue: ...

or a value:

...
EnvironmentVariables:
  - Name: TARGET_BUCKET
     Value:
       Fn::ImportValue: !Sub '${AWS::Region}-BuildBucket'

FindInMap

!FindInMap [ MapName, TopLevelKey, SecondLevelKey ]