cloudformation-extensions

Extensions to Amazon's CloudFormation Template JSON format.

Description

This is designed to make using Amazon's CloudFormation template format easier, more understandable, and more maintainable. CloudFormation templates are incredibly powerful, but quickly become complicated, and you end up with multiple thousands of lines of JSON which isn't very practical. Writing CloudFormation templates using cfnex retains the power of vanilla CloudFormation templates whilst increasing readability and maintainability.

Writing a cfnex extension is as easy as creating a function which takes an object and returns a promise. You can find examples of this in the extensions folder and a tutorial below.

Installation

Use the Docker Container (recommended)

docker run -v .:/cfnex joshbalfour/cfnex -i /cfnex/{inFile} -o /cfnex/{outFile}

(mapping the current directory to /cfnex in the container)

or grab from NPM

npm install -g cloudformation-extensions

cfnex -i {inFile} -o {outFile}

Writing Cfnex Templates

You write cfnex templates the same way you would regular CloudFormation templates, but with the ability to call cfnex extensions the same way you would "Intrinsic Functions" ( Fn::GetAtt, Fn::Join, etc. ), like so:

{ "cfnex::extensionName" : [ "aString", {"anObject": "argument2"}, 42 ] }

Where the array there are the arguments to be passed to the extension.

Out of the box cfnex comes with two extensions:

• include
• includeFile

include allows you to include another JSON or JS file, and includeFile allows you to include a raw file.

The output of an extension is then parsed as cfnex template, so you can do things recursively.

Built-in Extensions

include Extension

Example

A raw cloudformation.json file which looks like this:

{

    "AWSTemplateFormatVersion" : "2010-09-09",

    "Description" : "projectname Stack",
    "Parameters" : {
        "s3BucketName" : {
          "Type" : "String",
          "Description" : "S3 Bucket Name",
          "Default" : "project.name"
        },

        "redisSize": {
          "Type" : "String",
          "Description" : "Redis Size",
          "Default" : "cache.t2.micro"
        },

        "rdbmsSize": {
          "Type" : "String",
          "Description" : "RDBMS Size",
          "Default" : "db.t2.micro"
        }
    }

}

Becomes two files:

a root cloudformation.cfnex.json file

{
    "AWSTemplateFormatVersion" : "2010-09-09",

    "Description" : "projectname Stack",
    "Parameters" : { "cfnex::include" : [ "./parameters.json" ] },

}

and a separate parameters.json file

{
    "s3BucketName" : {
      "Type" : "String",
      "Description" : "S3 Bucket Name",
      "Default" : "project.name"
    },

    "redisSize": {
      "Type" : "String",
      "Description" : "Redis Size",
      "Default" : "cache.t2.micro"
    },

    "rdbmsSize": {
      "Type" : "String",
      "Description" : "RDBMS Size",
      "Default" : "db.t2.micro"
    }
}

include-file extension

A raw cloudformation.json file which includes this:

"UserData" : { "Fn::Base64" : { "Fn::Join" : ["", [
            "#!/bin/bash\n",
            "echo ECS_CLUSTER=", { "Ref": "EcsCluster" }, " >> /etc/ecs/ecs.config"
          ] ] } }

a root cloudformation.cfnex.json file

"UserData" : { "Fn::Base64" : { "cfnex::include-file" : [ "./ec2/boot.sh" ] } }

and a separate ./ec2/boot.sh file

#!/bin/bash
echo ECS_CLUSTER=<%cfnex { "Ref": "EcsCluster" } cfnex%>  >> /etc/ecs/ecs.config

Note the usage of <%cfnex tags in the included file, these can be used to include JSON in the included file.

Configuration

Your can override where cfnex looks for your extensions by having a .cfnexrc JSON file in the directory you run cfnex in which looks like this:

{
    "extensionsDirectory": "customDirName",
}

Writing your own extensions

You can write your own extensions by having an extensions directory, and within it your custom extensions, where the name of the extension is the filename, so if I wanted to refer to my extension as

{ "cfnex::includeYaml" : [ "myfile.yml" ] }

My extensions directory would look like this:

extensions
    - includeYaml.js

A cfnex extension is a function which returns a Promise which resolves to be an object. The function to be ran must be module.exported from the file. The function will be called with two parameters: args and context. args is whatever the extension was passed in the cfnex template file, so for our includeYaml extension it'd be

[ "myfile.yml" ]

context is an object which contains two properties:

• cwd - String - the absolute current working directory that you're being ran in
• logger - Object - a logging helper which has ok, error, debug, and info properties for you to use instead of plain console.log etc.

The object you return must have a property called output which is the output of your extension which will be the object can optionally have another property called contextChanges which should be an object. You can use this to override the context for any cfnex templates your extension returns.

CLI Usage

Usage:
  CloudFormation Extensions (cfnex) [OPTIONS] [ARGS]

Options: 
  -i, --inFilePath FILE  Input cfnex JSON file
  -o, --outFilePath DIR  Write to FILE rather than the console
      --cwd DIR          Override the working directory (defaults to the input file's directory)
  -k, --no-color         Omit color from output
      --debug            Show debug information
  -v, --version          Display the current version
  -h, --help             Display help and usage details

License