CloudShaped

Infrastructure as data code.

CloudFormation provides a nice way to provision AWS resources in a declarative way. But, programming in JSON can be painful.

CloudShaped provides a simple, extensible DSL for generating CloudFormation templates.

Add this line to your application's Gemfile:

gem 'cloud_shaped'

require 'cloud_shaped'
require 'json'

template = CloudShaped.template do |t|
  t.def_parameter "appName"
  t.def_resource "app", "AWS::Appity:AppApp", "Name" => t.ref("appName")
  t.def_output "appAddress", t.ref("app", "address")
end

puts JSON.pretty_generate(template)

outputs

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Parameters": {
    "appName": {
      "Type": "String"
    }
  },
  "Resources": {
    "app": {
      "Type": "AWS::Appity:AppApp",
      "Properties": {
        "Name": {
          "Ref": "appName"
        }
      }
    }
  },
  "Outputs": {
    "appAddress": {
      "Value": {
        "Fn::GetAtt": ["app", "address"]
      }
    }
  }
}

Declare CloudFormation resources using the def_resource method. It takes a resource name, type, and properties:

t.def_resource "adminEmail", "AWS::SNS::Topic",
  "Subscription" => [{"Protocol" => "email", "Endpoint" => "mdub@example.com"}]

If you prefer, you can set properties using a block:

t.def_resource "adminEmail", "AWS::SNS::Topic" do |topic|
  topic["Subscription"] = [
    { "Protocol" => "email", "Endpoint" => "mdub@example.com" }
  ]
end

Typically, the "type" argument will be a string specifying a CloudFormation resource type. However, it's also possible to provide a Ruby symbol, in which case def_resource will call the named method, passing remaining arguments. This allows common resource patterns to be abstracted as methods:

def t.email_topic(address)
  resource "AWS::SNS::Topic",
    "Subscription" => [{ "Protocol" => "email", "Endpoint" => address }]
end

t.def_resource "adminEmail", :email_topic, "mdub@example.com"

Sometimes it's necessary to embed files or even scripts in a CloudFormation template, but include references to stack parameters or resources; the resulting mess of "Fn::Join" and "Fn::GetAtt" can be hard to follow.

CloudShaped's interpolate function makes it easier; it detects references of the form {{RESOURCE}} or {{RESOURCE.ATTRIBUTE}} in a string, and generates "Ref" and "Fn::GetAtt" as appropriate, e.g.

script = <<-'BASH'
#!/bin/sh
... stuff ...
/usr/local/bin/cfn-signal -e 0 \
  --stack {{AWS::StackName}} --region {{AWS::Region}} \
  --resource thisHereInstance
BASH

t.interpolate(script) #=> ...
{
  "Fn::Join" =>
  [
    "\n",
    [
      "#!/bin/sh",
      "... stuff ...",
      "/usr/local/bin/cfn-signal -e 0 \\",
      {
        "Fn::Join" => [
          "",
          [
            "  --stack ",
            { "Ref" => "AWS::StackName" },
            " --region ",
            { "Ref" => "AWS::Region" },
            " \\"
          ]
        ]
      },
      "  --resource thisHereInstance"
    ]
  ]
}

For more info on the DSL, see:

• {CloudShaped.template}
• {CloudShaped::TemplateBuilder}

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