@cfn/diff

The purpose of this library is to make it easy to get an explanation of the difference between a CloudFormation Template and a Stack (if one exists) - similar to terraform plan.

Usage

const diff = require('@cfn/diff');

const { changeSetName, changes } = diff({
    // for aws-sdk calls
    credentials,
    // used for creating the CloudFormation Stack and ChangeSet
    stackName,
    description,
    roleArn,
    parameters,
    capabilities,
    template, // the actual (parsed) template, not the string templateBody!
    prefix, // a prefix added to the change set name
    detailed = false // will fetch S3 contents for nested stacks to include detailed differences
});

This is basically just a wrapper around CloudFormation ChangeSets with some additional logic for including Changes for Outputs, Parameters, Conditions as well as handling nested stacks. CloudFormation ChangeSets do not handle nested stacks correctly. They always return changes even when there are none. This library works around it by building a graph of the elements (resources, conditions, etc.) in a stack and trying to omit these false positives if there were no changes to a resource or any of its dependencies.