Fn::FindInMap enhancements

The AWS::LanguageExtensions transform enhances the functionality of the Fn::FindInMap intrinsic function in CloudFormation templates.

The Fn::FindInMap function is used to retrieve a value from a mapping defined in the Mappings section of a CloudFormation template. However, the standard Fn::FindInMap function has limitations, such as the inability to handle missing mappings or use a Fn::FindInMap function with some intrinsic functions embedded inside it.

The AWS::LanguageExtensions transform addresses these limitations by introducing the following enhancements:

• Default value support – You can specify a default value to be returned if a mapping is not found.

• Intrinsic function support – You can also use a wider range of intrinsic functions to define the fields of Fn::FindInMap than with the standard Fn::FindInMap function.

Declaration

JSON

{ "Fn::FindInMap" : [
    "MapName",
    "TopLevelKey",
    "SecondLevelKey",
    {"DefaultValue": "DefaultValue"}
  ]
}

YAML

Syntax for the full function name:

Fn::FindInMap:
  - MapName
  - TopLevelKey
  - SecondLevelKey
  - DefaultValue: DefaultValue

Syntax for the short form:

!FindInMap
  - MapName
  - TopLevelKey
  - SecondLevelKey
  - DefaultValue: DefaultValue

Parameters

DefaultValue

The value that Fn::FindInMap will resolve to if the TopLevelKey and/or SecondLevelKey can not be found from the MapName map. This field is optional.

All parameters MapName, TopLevelKey, SecondLevelKey, and DefaultValue can be an intrinsic function as long as it's able to resolve to a valid value during the transform.

Examples

The following examples demonstrate how to define the fields of Fn::FindInMap when you add the AWS::LanguageExtensions transform.

Using a default value

The following is an example of using a default value in the Fn::FindInMap function.

JSON

{
  //...
    "Transform": "AWS::LanguageExtensions",
    //...
    "Fn::FindInMap": [
      "RegionMap",
      { "Ref": "AWS::Region" },
      "InstanceType",
      { "DefaultValue": "t3.micro" }
    ]
  //...
}

YAML

Transform: 'AWS::LanguageExtensions'
#...
    !FindInMap 
        - 'RegionMap'
        - !Ref 'AWS::Region'
        - 'InstanceType'
        - DefaultValue: t3.micro
#...

Using intrinsic functions to define the top level key

The following is an example of using a Fn::FindInMap function with the Fn::Select and Fn::Split intrinsic functions embedded inside it to define the top level key.

JSON

{
  //...
  "Transform": "AWS::LanguageExtensions",
  //...
      "Fn::FindInMap": [
        "MyMap",
        {
          "Fn::Select": [
            0,
            {
              "Fn::Split": [
                "|",
                { "Ref": "InputKeys" }
              ]
            }
          ]
        },
        "SecondKey"
      ]
//...
}

YAML

Transform: 'AWS::LanguageExtensions'
#...
    !FindInMap: [MyMap, !Select [0, !Split [|, !Ref InputKeys]], SecondKey]
#...

Supported functions

You can use the following functions in the parameters of Fn::FindInMap: enhancements:

• Fn::FindInMap

• Fn::Join

• Fn::Sub

• Fn::If

• Fn::Select

• Fn::Length

• Fn::ToJsonString

• Fn::Split - Unless it’s used for the default value, Fn::Split has to be used in conjunction with intrinsic functions that produce a string, such as Fn::Join or Fn::Select.

• Ref

Related resources

For more information and examples that show how to use the Fn::FindInMap intrinsic function, see Fn::FindInMap.

For more information about the AWS::LanguageExtensions transform, see AWS::LanguageExtensions transform.