How To Convert From JSON to YAML With Ease

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

  "Description" : "AWS CloudFormation Sample Template DynamoDB_Table: This template demonstrates the creation of a DynamoDB table.  **WARNING** This template creates an Amazon DynamoDB table. You will be billed for the AWS resources used if you create a stack from this template.",

  "Parameters" : {
    "HaskKeyElementName" : {
      "Description" : "HashType PrimaryKey Name",
      "Type" : "String",
      "AllowedPattern" : "[a-zA-Z0-9]*",
      "MinLength": "1",
      "MaxLength": "2048",
      "ConstraintDescription" : "must contain only alphanumberic characters"
    },

    "HaskKeyElementType" : {
      "Description" : "HashType PrimaryKey Type",
      "Type" : "String",
      "Default" : "S",
      "AllowedPattern" : "[S|N]",
      "MinLength": "1",
      "MaxLength": "1",
      "ConstraintDescription" : "must be either S or N"
    },

    "ReadCapacityUnits" : {
      "Description" : "Provisioned read throughput",
      "Type" : "Number",
      "Default" : "5",
      "MinValue": "5",
      "MaxValue": "10000",
      "ConstraintDescription" : "must be between 5 and 10000"
    },

    "WriteCapacityUnits" : {
      "Description" : "Provisioned write throughput",
      "Type" : "Number",
      "Default" : "10",
      "MinValue": "5",
      "MaxValue": "10000",
      "ConstraintDescription" : "must be between 5 and 10000"
    }
  },

  "Resources" : {
    "myDynamoDBTable" : {
      "Type" : "AWS::DynamoDB::Table",
      "Properties" : {
        "AttributeDefinitions": [ {
          "AttributeName" : {"Ref" : "HaskKeyElementName"},
          "AttributeType" : {"Ref" : "HaskKeyElementType"}
        } ],
        "KeySchema": [
          { "AttributeName": {"Ref" : "HaskKeyElementName"}, "KeyType": "HASH" }
        ],
        "ProvisionedThroughput" : {
          "ReadCapacityUnits" : {"Ref" : "ReadCapacityUnits"},
          "WriteCapacityUnits" : {"Ref" : "WriteCapacityUnits"}
        }
      }
    }
  },

  "Outputs" : {
    "TableName" : {
      "Value" : {"Ref" : "myDynamoDBTable"},
      "Description" : "Table name of the newly created DynamoDB table"
    }
  }
}

Some people have no problem reading JSON and working with it’s “large” number of curly braces. I personally prefer to no have to do that. So, after looking for information and modifying it to suite my needs, I am now able to convert the above template into the following YAML file:

---
AWSTemplateFormatVersion: '2010-09-09'
Description: 'AWS CloudFormation Sample Template DynamoDB_Table: This template demonstrates
  the creation of a DynamoDB table.  **WARNING** This template creates an Amazon DynamoDB
  table. You will be billed for the AWS resources used if you create a stack from
  this template.'
Parameters:
  HaskKeyElementName:
    Description: HashType PrimaryKey Name
    Type: String
    AllowedPattern: "[a-zA-Z0-9]*"
    MinLength: '1'
    MaxLength: '2048'
    ConstraintDescription: must contain only alphanumberic characters
  HaskKeyElementType:
    Description: HashType PrimaryKey Type
    Type: String
    Default: S
    AllowedPattern: "[S|N]"
    MinLength: '1'
    MaxLength: '1'
    ConstraintDescription: must be either S or N
  ReadCapacityUnits:
    Description: Provisioned read throughput
    Type: Number
    Default: '5'
    MinValue: '5'
    MaxValue: '10000'
    ConstraintDescription: must be between 5 and 10000
  WriteCapacityUnits:
    Description: Provisioned write throughput
    Type: Number
    Default: '10'
    MinValue: '5'
    MaxValue: '10000'
    ConstraintDescription: must be between 5 and 10000
Resources:
  myDynamoDBTable:
    Type: AWS::DynamoDB::Table
    Properties:
      AttributeDefinitions:
      - AttributeName:
          Ref: HaskKeyElementName
        AttributeType:
          Ref: HaskKeyElementType
      KeySchema:
      - AttributeName:
          Ref: HaskKeyElementName
        KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits:
          Ref: ReadCapacityUnits
        WriteCapacityUnits:
          Ref: WriteCapacityUnits
Outputs:
  TableName:
    Value:
      Ref: myDynamoDBTable
    Description: Table name of the newly created DynamoDB table

Solution

Now, in my personal opinion, the above YAML version is much easier to read than the JSON version. If you do have similar notions, please take a look at the below script. It is mostly self explanatory and also displays a bit of help if you miss something on command line. What is does though is convert one format into another and back again. This lets me work on the CloudFormation templates in YAML then convert them into proper JSON for upload into AWS.

#!/usr/bin/env ruby

require 'yaml'
require 'json'
require 'optparse'
require 'ostruct'
require 'fileutils'

#quit unless our script gets two command line arguments
unless ARGV.length == 3
  puts "Dude, not the right number of arguments."
  puts "Usage: ruby YJ_Convert.rb [-j][-y] json_file.json yaml_file.yaml\n"
  exit
end

$json_file = ARGV[1]
$yaml_file = ARGV[2]

options = OpenStruct.new
OptionParser.new do |opt|
  opt.on('-j', '--json', 'Convert to JSON') { |o| options.json = o }
  opt.on('-y', '--yaml', 'Convert to YAML') { |o| options.yaml = o }
end.parse!

case
  when options.yaml == true
    y_file = File.open("#{$yaml_file}", 'a')
    y_file.write(YAML.dump(JSON.parse(IO.read($json_file))))
    y_file.close
    puts "Converted to YAML. Output file is #{$yaml_file}"

  when options.json == true
    j_file = YAML.load_file(File.open("#{$yaml_file}", 'r'))
    File.write "#{$json_file}", JSON.pretty_generate(j_file)
    puts "Converted to JSON. Output file is #{$json_file}"
end