This Ruby gem is to assist with the development of custom resources for CloudFormation using the Ruby runtime.

Add this line to your application's Gemfile:

gem 'aws_cloudformation_helper'

And then execute:

$ bundle

Or install it yourself as:

$ gem install aws_cloudformation_helper

Install this gem into your Lambda environment using bundle install or by bundling this gem in a Lambda layer.

Once the Ruby gem is installed, use the code template below for the main Lambda function to begin:

require 'aws_cloudformation_helper'

def create
  # Add code to handle CloudFormation Create event
end

def delete
  # Add code to handle CloudFormation Delete event
end

def update
  # Add code to handle CloudFormation Update event
end

def lambda_handler(event:, context:)
  # Initializes CloudFormation Helper library
  @cfn_helper = AWS::CloudFormation::Helper.new(self, event, context)

  # Add additional initialization code here

  # Executes the event
  @cfn_helper.event.execute
end

The create, delete, and update methods will send a success response to CloudFormation when the method finishes executing, and a failure response will be sent when exceptions are raised.

By default, the logging level is set to :info. To enable another logging level, add a line to the initialization section of the lambda_handler function. The logger is the standard Ruby logger provided by the Ruby stdlib.

The stdout and stderr variables can be reassigned to store log entries in another stream or file. By default, the default logger logs to STDOUT and the error logger (only for logger.error messages) logs to STDERR.

See more info here: https://ruby-doc.org/stdlib-2.7.0/libdoc/logger/rdoc/Logger.html

Below is a sample code block on enabling debug logging and redirecting stdout/stderr:

def lambda_handler(event:, context:)
  # Initializes CloudFormation Helper library
  @cfn_helper = AWS::CloudFormation::Helper.new(self, event, context)

  # Add additional initialization code here
  @cfn_helper.logger.log_level = :debug
  @cfn_helper.logger.stdout = $stdout
  @cfn_helper.logger.stderr = $stderr

  # Executes the event
  @cfn_helper.event.execute
end

The event data and context object are available from the @cfn_helper variable in the main class. Access this data by calling @cfn_helper.event and @cfn_helper.context.

Additional response data can also be sent back to CloudFormation stack, ex: @cfn_helper.event.response_data['Foo']='Bar'

Custom physical_resource_id can be sent back to CloudFormation stack by calling @cfn_helper.event.update_physical_resource_id('custom-id') # returns boolean. Please note, this only works when CloudFormation stack did not provide an id already.

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install.

Bug reports and pull requests are welcome on GitHub at https://github.com/jeffreycoe/aws_cloudformation_helper.

The gem is available as open source under the terms of the MIT License.