cfnplan

cfnplan (CloudFormation Plan) is a simple tool to help you plan for AWS CloudFormation stack updates. It's inspired by the (awesome) terraform plan mode.

Goal

The goal of cfnplan is to:

1. Avoid having to read your CloudFormation template to work out resource dependencies
2. Avoid having to apply the "update" vs "replace" rules manually, which you need to read the docs to learn

Install

cfnplan is available via PyPi:

$ pip install cfnplan

Example

Currently cfnplan only lists dependencies between parameters, mappings, outputs, conditions and resources, an example of the AWS "WordPress scalable and durable" template:

$ cfnplan describe "tests/templates/WordPress_Multi_AZ.template"
DBSecurityGroup (AWS::RDS::DBSecurityGroup)
  <== AWS::Region
  <== SSHLocation
  <== ElasticLoadBalancer (AWS::ElasticLoadBalancing::LoadBalancer)
  <== Is-EC2-Classic
  <== Is-EC2-VPC
  <== WebServerSecurityGroup (AWS::EC2::SecurityGroup)
WebServerSecurityGroup (AWS::EC2::SecurityGroup)
  <== SSHLocation
  <== ElasticLoadBalancer (AWS::ElasticLoadBalancing::LoadBalancer)

# ... snip ...

Or with the full dependency tree:

$ cfnplan describe "tests/templates/WordPress_Multi_AZ.template" --verbose
DBSecurityGroup (AWS::RDS::DBSecurityGroup)
  <== WebServerSecurityGroup (AWS::EC2::SecurityGroup)
    <== ElasticLoadBalancer (AWS::ElasticLoadBalancing::LoadBalancer)
    <== SSHLocation
  <== SSHLocation
  <== ElasticLoadBalancer (AWS::ElasticLoadBalancing::LoadBalancer)
  <== Is-EC2-VPC
    <== AWS::Region
  <== Is-EC2-Classic
    <== Is-EC2-VPC
      <== AWS::Region
    <== AWS::Region
  <== AWS::Region
WebServerSecurityGroup (AWS::EC2::SecurityGroup)
  <== ElasticLoadBalancer (AWS::ElasticLoadBalancing::LoadBalancer)
  <== SSHLocation

# ... snip ...