cfn-reducer

Reduces your way too complex CloudFormation templates into something you can put under version control.

Why?

Because before you start using Troposphere, your CloudFormation templates can turn to 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.

Install

$ npm install cfn-reducer

Usage: Command Line

The command line reducer accepts a path to a CloudFormation template and optional key-value pairs of stack parameters. Output goes to stdout and can be redirected to a file.

$ ./node_modules/bin/cfn-reducer \
    MyTemplate.template \
        MyParam1=some-value-1 \
        MyParam2=some-value-2 \
    > MyReducedTemplate.template

Usage: Programmatically

var fs = require('fs');
var CfnReducer = require('cfn-reducer');
 
// Load your template into an object.
var file = 'MyTemplate.template';
var template = JSON.parse(fs.readFileSync(file));
 
// Specify necessary parameters.
var stackParams = {
    MyParam1: 'some-value-1',
    MyParam2: 'some-value-2',
};
 
// Run the reducer.
var options = {
    stackParams: stackParams,
};
var reducer = new CfnReducer(template, options);
var reduced = reducer.reduce();
 
// Show me the magic!
var output = JSON.stringify(reduced, null, '\t');
console.log(output);

Reductions Made

Needs to be fleshed out. Take a look at the test folder for now, and keep in mind that all transformations are done recursively, until nothing more can be reduced.

Replacements

• Ref - Substitutes all Refs that refer to parameters explicitly passed into the template.

Simplifications

The following intrinsics will be simplified as much as possible.

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

Todo

• Make API more flexible
• Integrate substacks?
• Strip unused mappings/conditions/[...]?