Reference

Library Structure

• Cfgen.Template provides the constructs needed to create a template, add resources, parameters and outputs, and then serialise it with Yojson
• Cfgen.BaseConstructs contains the generated CloudFormation constructs arranged into an AWS and Alexa namespace, with helpers for creating resource properties (and their associated sub-types)
• Cfgen.Helpers contains DSL helpers for constructing inline values for AWS-specific DSLs, like IAM policies.

How To

Creating a stack

open Cfgen

let my_template_creator =
  let template = Template.make () in
  template

Creating resources

• Identify the resource module from Cfgen.BaseConstructs, which are in a Namespace.Service.Resource hiearchy.

For example, AWS IAM Roles are in Cfgen.BaseConstructs.AWS.IAM.Role module

• Construct the resource properties using the make_properties helper in the module

(These helpers save you needing to specify optional values on resources with lots of properties, which is very common in AWS)

open Cfgen.BaseConstructs

let create_role template =
  let tags = [AWS.IAM.Role.make_tag ~key:"Environment" ~value:"Development" ()] in
  let props = AWS.IAM.Role.make_properties
    ~assume_role_policy_document: assume_role
    ~tags
    () in
  ...

Some properties have record types, which also have their own make_<type_name> function

• Add the resource to the template, specifying a logical_id to uniquely identify it in the template

open Cfgen.BaseConstructs

let create_role =
  let props = ... in
  Template.add_resource template "MyRole" (module AWS.IAM.Role) props ()

Reference resource attributes in other resource properties

Defining stack parameters

Defining stack outputs

Serialising a stack to JSON