Reduces your way too complex CloudFormation templates into something you can understand and verify before running it in production.

Because before you start using Troposphere, your CloudFormation templates can turn into unreadable, unverifiable JSON spaghetti. Passing parameters into your template can help you flatten out all the messy logic within the template, letting you generate specific files for different purposes (like staging/production) and put these under version control. It can even integrate your sub-templates back into the main template.

$ npm install cfn-reducer

var fs = require('fs');
var CfnReducer = require('cfn-reducer');

// Create a reducer for your template, with optional parameters and sub-templates.
var reducer = new CfnReducer({
	template: JSON.parse(fs.readFileSync('./Template.template')), // Required.
	stackParams: {
		Param1: 'Value1',
		Param2: 'Value2',
	},
	subTemplates: {
		'TemplateURLToSubTemplate1': JSON.parse(fs.readFileSync('./SubTemplate1.template')),
		'TemplateURLToSubTemplate2': JSON.parse(fs.readFileSync('./SubTemplate2.template')),
	},
});

// Run it and display the reduced template.
var reduced = reducer.reduce();
var output = JSON.stringify(reduced, null, '\t');
console.log(output);

Reductions are made recursively, until nothing more can be reduced.

All stack parameters passed to the reducer will be inserted in place of their corresponding Refs.

The following intrinsic functions will be simplified as much as possible:

• Fn::And
• Fn::Equals
• Fn::FindInMap
• Fn::If
• Fn::Join
• Fn::Not
• Fn::Or
• Fn::Select

Fn::And will be reduced to true if both conditions can be evaluated to true, Fn::FindInMap will be replaced by its Mappings lookup, Fn::Join will be replaced by its concatenation if all arguments can be evaluated to strings, etc.

A resource with a Condition that evaluates to true will have its Condition removed. A resource with a Condition that evaluates to false will be removed altogether.

Resources of type AWS::CloudFormation::Stack can be reduced and integrated back into the main template. All things (conditions, mappings, outputs, resources) in the sub-template will be prefixed with the resource's name when being integrated back into the main template.

Sub-template integration is triggered when the subTemplates object is passed in, containing the full template objects that TemplateURL references refer to.

As a result of reductions and simplifications, certain parts of the template might no longer be needed and are therefore removed:

• Parameters that were passed in as stackParams.
• Mappings that have been resolved and are no longer referenced.
• Conditions that have been evaluated and inlined.

Top-level keys that have become empty are removed.

• Refactor the code.
• Make name-prefixing more robust.