CloudFormation Explode List Macro

This is a CloudFormation Macro that loops over a list and generates a unique resource for each item in it.

Example

Here's a CloudFormation template before the macro transformation is applied:

AWSTemplateFormatVersion: "2010-09-09"
Transform: ExplodeList

Resources:
  TestRoute:
    Type: AWS::EC2::Route
    ExplodeList:
      - 10.0.48.0/24
      - 10.0.112.0/24
      - 10.0.176.0/24
    Properties:
      DestinationCidrBlock: !InsListItem
      TransitGatewayId: tgw-a1b2c3d4
      RouteTableId: rtb-a1b2c3e4

And here's the output which is then sent to CloudFormation for deployment.

AWSTemplateFormatVersion: "2010-09-09"

Resources:
  TestRouteedb024d:
    Type: AWS::EC2::Route
    Properties:
      DestinationCidrBlock: 10.0.48.0/24
      TransitGatewayId: tgw-a1b2c3d4
      RouteTableId: rtb-a1b2c3e4

  TestRoute11180275:
    Type: AWS::EC2::Route
    Properties:
      DestinationCidrBlock: 10.0.112.0/24
      TransitGatewayId: tgw-a1b2c3d4
      RouteTableId: rtb-a1b2c3e4

  TestRoute115a027f:
    Type: AWS::EC2::Route
    Properties:
      DestinationCidrBlock: 10.0.176.0/24
      TransitGatewayId: tgw-a1b2c3d4
      RouteTableId: rtb-a1b2c3e4

Allowed List Types

YAML and JSON Lists and CommaDelimitedLists are allowed. These values can be passed directly to the resource's ExplodeList property, or via template Parameters using the !RefList tag.

Parameters:
  SomeList:
    Type: CommaDelimitedList
    Default: aaaaa,bbbbb,ccccc

Resources:
  SomeResource:
    Type: AWS::Some::Resource
    ExplodeList: !RefList SomeList

  SomeOtherResource:
    Type: AWS::SomeOther::Resource
    ExplodeList: aaaaa,bbbbb,ccccc

  AnotherResource:
    Type: AWS::Another::Resource
    ExplodeList:
      - aaaaa
      - bbbbb
      - ccccc

Note: Since macros preprocess CloudFormation templates, references to other resources and outputs thereof cannot be passed to the ExplodeList property. In other words, the list values need to be available at the time of template preprocessing.

Deploy