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Toolkit and Ruby DSL for automating infrastructure using AWS CloudFormation
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Cfer is a lightweight toolkit for managing CloudFormation templates.

Read about Cfer here.

Sign up for the Cfer mailing list to receive updates when changes are made. Cfer is a slow-moving project, so you can expect around one or two updates per year at most.


Cfer is pre-1.0 software, and may contain bugs or incomplete features. Please see the license for disclaimers.

If you would like support or guidance on Cfer, or CloudFormation in general, I offer DevOps consulting services. Please Contact me and I'll be happy to discuss your needs.

You can also find me at @tilmonedwards. If you use Cfer, or are considering it, I'd love to hear from you.


Add this line to your application's Gemfile:

gem 'cfer'

And then execute:

$ bundle

Or install it yourself as:

$ gem install cfer


To quickly see Cfer in action, try converging the example stacks:

cfer converge vpc -t examples/vpc.rb --profile [YOUR-PROFILE] --region [YOUR-REGION]
cfer converge instance -t examples/instance.rb --profile [YOUR-PROFILE] --region [YOUR-REGION] KeyName=[YOUR-EC2-SSH-KEY]

You should see something like this:


Command line

    converge     Create or update a cloudformation stack according to the template
    delete       Deletes a CloudFormation stack
    describe     Fetches and prints information about a CloudFormation
    estimate     Prints a link to the Amazon cost caculator estimating the cost of the resulting CloudFormation stack
    generate     Generates a CloudFormation template by evaluating a Cfer template
    help         show help
    tail         Follows stack events on standard output as they occur

Template Anatomy

See the examples directory for some examples of complete templates.


Parameters may be defined using the parameter function:

parameter :ParameterName,
  type: 'String',
  default: 'ParameterValue'

Any parameter can be referenced either in Ruby by using the parameters hash:


Parameters can also be used in a CloudFormation reference by using the Fn::ref function:



Resources may be defined using the resource function:

resource :ResourceName, 'AWS::CloudFormation::CustomResource', AttributeName: {:attribute_key => 'attribute_value'} do
  property_name 'property_value'

Gets transformed into the corresponding CloudFormation block:

"ResourceName": {
  "Type": "AWS::CloudFormation::CustomResource",
  "AttributeName": {
    "attribute_key": "attribute_value"
  "Properties": {
    "PropertyName": "property_value"


Outputs may be defined using the output function:

output :OutputName, Fn::ref(:ResourceName)

Outputs may be retireved from other stacks anywhere in a template by using the lookup_output function.

lookup_output('stack_name', 'output_name')

Including code from multiple files

Templates can get pretty large, and splitting template code into multiple files can help keep things more manageable. The include_template function works in a similar way to ruby's require_relative, but within the context of the CloudFormation stack:

include_template 'ec2.rb'

You can also include multiple files in a single call:


The path to included files is relative to the base template file (e.g. the converge command -t option).


Embedding the Cfer SDK involves interacting with two components: The Client and the Stack. The Cfer Client is the interface with the Cloud provider.

Basic API

The simplest way to use Cfer from Ruby looks similar to the CLI:

  Cfer.converge! '<stack-name>', template: '<template-file>'

This is identical to running cfer converge <stack-name> --template <template-file>, but is better suited to embedding in Rakefiles, chef recipes, or your own Ruby scripts. See the Rakefile in this repository for how this might look.

Cfn Client

The Client is a wrapper around Amazon's CloudFormation client from the AWS Ruby SDK. Its purpose is to interact with the CloudFormation API.

Create a new client: <stack_name>)

Cfer::Cfn::Client also accepts options to be passed into the internal Aws::CloudFormation::Client constructor.


Creates or updates the CloudFormation stack to match the input stack object. See below for how to create Cfer stack objects.


tail(options = {})

Yields to the specified block for each CloudFormation event that qualifies given the specified options.

client.tail number: 1, follow: true do |event|
  # Called for each CloudFormation event, as they occur, until the stack enters a COMPLETE or FAILED state.

Cfer Stacks

A Cfer stack represents a baked CloudFormation template, which is ready to be converted to JSON.

Create a new stack:


stack = Cfer::stack_from_file(<file>, client: <client>)


stack = Cfer::stack_from_block(client: <client>) do
  # Stack definition goes here


This project uses git-flow. Please name branches and pull requests according to that convention.

Always use --no-ff when merging into develop or master.

This project also contains a Code of Conduct, which should be followed when submitting feedback or contributions to this project.

New features

  • Branch from develop
  • Merge into develop
  • Name branch feature/<feature-name>

Unreleased bugs

  • Branch from develop
  • Merge into develop
  • Name branch bugfix/<issue-id>

Bugfixes against releases

  • Branch from master
  • Merge into develop and master
  • Name branch hotfix/<issue-id>


  • Branch from develop
  • Merge into develop and master
  • Name branch release/<major.minor>

Release Notes

Change Log

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