About

SuperStacker is a tool for writing cloudformation templates in a ruby DSL.

The DSL is parsed and then output as JSON, ready for use with the CloudFormation toolchain.

Knowledge of CloudFormation templates and basic Ruby knowledge is assumed.

Definitions

Definitions are a declarative way of expressing a cloudformation template. They allow us to declare parameters, resources, outputs and the description in any order we want. SuperStacker handles compiling these and building the relevant JSON object.

description

The description for a cloudformation stack is specified using the description definition, as shown below:

description "description for this stack"

This definition is unique in that it should only be declared once.

See AWS documentation for further information.

parameter

A parameter to be passed through to the CloudFormation template during stack creation time.

parameter "ParameterName", "Type" => "String", "AllowedValues" => ["value1", "value2"]

The parameter keyword knows how to handle all of the properties specified in the AWS documentation. Please consult that for information on accepted properties.

resource

A resource is a nice clean interface for building a Hash. This is probably best explained as an example:

resource "TestName", "MyFakeType" do
  Key "Value"
  NestedHash do
    NestedKey "NestedValue"
  end
end

would become

{
  "TestName" => {
    "Type" => "MyFakeType",
    "Key" => "Value",
    "NestedHash" => {
      "NestedKey" => "NestedValue"
    }
  }
}

Resources should be able to represent any of the resources available in AWS. Please consult the AWS Documentation for a complete list of available resources, types and properties.

output

A output is some parameter that you want returned as a result of the stacks creation. These are often used as parameters for subsequent stacks.

output "SomeOutputKey", "SomeOutputValue", "SomeOutputDescription"

Please take a look at the AWS documentation for a more detailed description of outputs.

mapping

Mappings enable you to specify conditional parameter values in your template. When used with the intrinsic function Fn::FindInMap, it works like a Case statement or lookup table.

mapping "TestMap" do
  MapKey do
    SomeValue "SomeString"
  end
end

would become

{
  "TestMap" => {
    "MapKey" => {
      "SomeValue" => "SomeString"
    }
  }
}

Please take a look at the AWS documentation for a more detailed description of mappings.

Shorthand Intrinsic Functions

All of the below functions are essentially shorthand for the AWS cloudformation functions, and are calculated server side once the template has been uploaded.

Please see the AWS documentation for a full list of available functions.

Fn::Base64

Returns the Base64 representation of the input string.

Fn::Base64("SomeString") => { "Fn::Base64" => "SomeString" }

Please see the AWS documentation for further information.

Fn::FindInMap

Returns the value of a key from a mapping declared in the Mappings section.

Fn::FindInMap("SomeMap", "SomeKey", "SomeValue") => { "Fn::FindInMap" => [ "SomeMap", "SomeKey", "SomeValue" ] }

Please see the AWS documentation for further information.

Fn::GetAtt

Returns the value of an attribute from a resource in the template.

Fn::GetAtt("SomeResource", "SomeAttribute") => { "Fn::GetAtt" => [ "SomeAttribute", "SomeAttribute" ] }

Please see the AWS documentation for further information.

Fn::GetAZs

Returns an array that lists all Availability Zones for the specified region.

If no region is specified, the region the stack was created in is used.

Fn::GetAZs => { "Fn::GetAZs" => "" }

Please see the AWS documentation for further information.

Fn::Join

Appends a set of values into a single value, separated by the specified delimiter. If a delimiter is the empty string, the set of values are concatenated with no delimiter.

Fn::Join(" ", ["this", "is", "a", "list"] => { "Fn::Join" => [ " ", ["this", "is", "a", "list" ] ] }

Please see the AWS documentation for further information.

Fn::Select

Returns a single object from a list of objects by index.

Fn::Select("1", ["zero", "one", "two"]) => { "Fn::Select" => [ "1", ["zero", "one", "two" ] ] }

Please see the AWS documentation for further information.

Ref

Ref is used to create a reference to another element of the CloudFormation template.

Ref("SomeElement") => { "Ref" => "SomeElement" }

Please see the AWS documentation for further information.

Funnies

escape

Due to the way Ruby works, hyphens can not be part of method names so a declaration like the following will not work:

mapping 'RegionMap' do
  us-west-2 do
    AMI 'ami-aaaabbbb'
  end
end

To get around this, the escape function is provided:

mapping 'RegionMap' do
  escape 'us-west-2' do
    AMI 'ami-aaaabbbb'
  end
end

Examples

Example stacks have been included in the exampes/ directory. Please consult them for practical use cases. I'll be updating this directory with more examples as I add features so check back regularly.

To check the output of a sample do something like:

super-stacker stack examples/ec2-instance/

Configuration

Interfacing with the AWS api requires an access key, SuperStacker expects this file to be at ~/.awscli in the following format:

[default]
aws_access_key_id = XXXXXXXXXXXXXXXXXXXX
aws_secret_access_key = XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
region = ap-southeast-2