cfndsl

AWS Cloudformation templates are an incredibly powerful way to build sets of resources in Amazon's AWS environment. Unfortunately, because they are specified in JSON, they are also difficult to write and maintain:

• JSON does not allow comments

• All structures are JSON, so it is sometimes easy for a person reading a template to get lost.

• References and internal functions have a particularly unpleasant syntax.

The cnfdsl gem provides a simple DSL that allows you to write equivalent templates in a more friendly language and generate the correct json templates by running ruby.

Getting Started

sudo gem install cfndsl

Now write a template in the dsl

CloudFormation {
  Description "Test"
  
  Parameter("One") {
    String
    Default "Test"
	MaxLength 15
  }
 
  Output(:One,FnBase64( Ref("One")))

  Resource("MyInstance") {
	Type "AWS::EC2::Instance"
	Property("ImageId","ami-14341342")
  }
  
}

Then run cfndsl on the file

chris@raspberrypi:~/git/cfndsl$ cfndsl test.rb | json_pp
{
   "Parameters" : {
      "One" : {
         "Type" : "String",
         "Default" : "Test",
         "MaxLength" : 15
      }
   },
   "Resources" : {
      "MyInstance" : {
         "Type" : "AWS::EC2::Instance",
         "Properties" : {
            "ImageId" : "ami-14341342"
         }
      }
   },
   "AWSTemplateFormatVersion" : "2010-09-09",
   "Outputs" : {
      "One" : {
         "Value" : {
            "Fn::Base64" : {
               "Ref" : "One"
            }
         }
      }
   },
   "Description" : "Test"
}

Aside: that is correct - a significant amount of the development for this gem was done on a Raspberry Pi.

Samples

There is a more detailed example in the samples directory. The file "autoscale.template" is one of the standard Amazon sample templates. "autoscale.rb" generates an equivalent template file.