The stratosphere package

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Versions0.1.0, 0.1.0, 0.1.1, 0.1.2, 0.1.2.1, 0.1.3, 0.1.4, 0.1.5, 0.1.6, 0.2.0, 0.2.1, 0.2.2, 0.3.0, 0.3.1, 0.4.0, 0.4.1, 0.4.2
Change logCHANGELOG.md
Dependenciesaeson (>=0.11), aeson-pretty (>=0.7), base (>=4.8 && <5), bytestring, ede, lens (>=4.5), stratosphere, system-fileio, system-filepath, template-haskell (>=2.0), text (>=1.1), unordered-containers (>=0.2) [details]
LicenseMIT
MaintainerDavid Reaver
CategoryAWS, Cloud
Home pagehttps://github.com/frontrowed/stratosphere#readme
Bug trackerhttps://github.com/frontrowed/stratosphere/issues
Source repositoryhead: git clone https://github.com/frontrowed/stratosphere
Executablesrds-master-replica, ec2-with-eip
UploadedTue Apr 19 16:33:11 UTC 2016 by jdreaver

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Readme for stratosphere-0.1.0

Stratosphere: AWS CloudFormation in Haskell

Build Status

AWS CloudFormation is a system that provisions and updates Amazon Web Services (AWS) resources based on declarative templates. Common criticisms of CloudFormation include the use of JSON as the template language and limited error-checking, often only available in the form of run-time errors and stack rollbacks. By wrapping templates in Haskell, we are able to easily construct them and help ensure correctness.

The goals of stratosphere are to:

Example

Here is an example of a Template that creates an EC2 instance, along with the JSON output:

{-# LANGUAGE OverloadedLists #-}
{-# LANGUAGE OverloadedStrings #-}

module Main where

import qualified Data.ByteString.Lazy.Char8 as B
import Stratosphere

main :: IO ()
main = B.putStrLn $ encodeTemplate instanceTemplate

instanceTemplate :: Template
instanceTemplate =
  template
  [ resource "EC2Instance" (
    EC2InstanceProperties $
    ec2Instance
    "ami-22111148"
    & eciKeyName ?~ (Ref "KeyName")
    )
    & deletionPolicy ?~ Retain
  ]
  & description ?~ "Sample template"
  & parameters ?~
  [ parameter "KeyName" "AWS::EC2::KeyPair::KeyName"
    & description ?~ "Name of an existing EC2 KeyPair to enable SSH access to the instance"
    & constraintDescription ?~ "Must be the name of an existing EC2 KeyPair."
  ]
{
  "Description": "Sample template",
  "Parameters": {
    "KeyName": {
      "Description": "Name of an existing EC2 KeyPair to enable SSH access to the instance",
      "ConstraintDescription": "Must be the name of an existing EC2 KeyPair.",
      "Type": "AWS::EC2::KeyPair::KeyName"
    }
  },
  "Resources": {
    "EC2Instance": {
      "DeletionPolicy": "Retain",
      "Type": "AWS::EC2::Instance",
      "Properties": {
        "KeyName": {
          "Ref": "KeyName"
        },
        "ImageId": "ami-22111148"
      }
    }
  }
}

Please see the examples directory for more in-depth examples.

Value Types

CloudFormation resource parameters can be literals (strings, integers, etc), references to another resource or a Parameter, or the result of some function call. We encapsulate all of these possibilities in the Val a type.

We recommend using the OverloadedStrings extension to reduce the number of Literals you have to use.

Note that CloudFormation represents numbers and bools in JSON as strings, so we had to some types called Integer' and Bool' to override the aeson instances. In a future version we plan on using our own JSON encoder/decoder to get around this.

Lenses

Almost every CloudFormation resource has a handful of required arguments, and many more optional arguments. Each resource is represented as a record type with optional arguments wrapped in Maybe. Each resource also comes with a constructor that accepts required resource parameters as arguments. This allows the user to succinctly specify the resource parameters they actually use without adding too much noise to their code.

To specify optional arguments, we recommend using the lens operators & and ?~. In the example above, the ec2Instance function takes the AMI as an argument, since it is required by the EC2Instance resource type. Then, the optional EC2 key name is specified using the & and ?~ lens operators.

This approach is very similar to the approach taken by the amazonka library. See this blog post for an explanation.

Auto-generation

All of the resources and resource properties are auto-generated from JSON files and are placed in library-gen/. The gen/ directory contains the auto-generator code and the JSON model files. We include the library-gen/ directory in git so the build process is simplified. To build library-gen from scratch and then build all of stratosphere, just run the very short build.sh script. You can pass stack args to the script too, so run ./build.sh --fast to build the library without optimization. This is useful for development.

In the future, it would be great to not have to include the auto-generated code in git.

Also, there is a file called scraper.py that scrapes a given CloudFormation resource documentation page to produce the JSON model. It isn't perfect, but it helps a lot.

Contributing

Feel free to raise any issues, or even just make suggestions, by filing a Github issue.

Future Work

The library is usable in its current state and it is already much more enjoyable to work with than writing JSON templates by hand, but there are of course a few possible future improvements: