Cfoo

Cfoo (pronounced “sifu”) lets you write your CloudFormation
templates in YAML, and makes it easier with some helpers.

Installation

Cfoo can be installed as a Ruby Gem

$ gem install cfoo

Usage

1. Write your CloudFormation templates using Cfoo YAML

2. Turn your Cfoo templates into normal CloudFormation templates

   $ cfoo web-server.template.yml database.template.yml > web-stack.template.json

3. Create your stack with CloudFormation

   $ cfn-create-stack --stack-name WebStack -f web-stack.template.json

Templates

Comparison with standard CloudFormation templates

Snippet from a CloudFormation template (based on this example):

"Properties": {
  "ImageId" : { "Fn::FindInMap" : [ "AWSRegion2AMI", { "Ref" : "AWS::Region" }, "AMI" ] },
  "InstanceType"   : { "Ref" : "InstanceType" },
  "SecurityGroups" : [ {"Ref" : "FrontendGroup"} ],
  "KeyName"        : { "Ref" : "KeyName" },
  "UserData"       : { "Fn::Base64" : { "Fn::Join" : ["", [
    "#!/bin/bash -v\n",
    "yum update -y aws-cfn-bootstrap\n",
    "function error_exit\n",
    "{\n",
    "  /opt/aws/bin/cfn-signal -e 1 -r \"$1\" '", { "Ref" : "WaitHandle" }, "'\n",
    "  exit 1\n",
    "}\n",
    "/opt/aws/bin/cfn-init -s ", { "Ref" : "AWS::StackId" }, " -r WebServer ",
    "    --region ", { "Ref" : "AWS::Region" }, " || error_exit 'Failed to run cfn-init'\n",
    "/opt/aws/bin/cfn-signal -e 0 -r \"cfn-init complete\" '", { "Ref" : "WaitHandle" }, "'\n"
  ]]}}
}

Equivalent Cfoo template snippet:

Properties:
  ImageId : AWSRegion2AMI[$(AWS::Region)][AMI]
  InstanceType: $(InstanceType)
  SecurityGroups:
     - $(FrontendGroup)
  KeyName: $(KeyName)
  UserData: !Base64 |
    #!/bin/bash -v
    yum update -y aws-cfn-bootstrap
    function error_exit
    {
      /opt/aws/bin/cfn-signal -e 1 -r "\$1" '$(WaitHandle)'
      exit 1
    }
    /opt/aws/bin/cfn-init -s $(AWS::StackId) -r WebServer --region $(AWS::Region) || error_exit 'Failed to run cfn-init'
    /opt/aws/bin/cfn-signal -e 0 -r "cfn-init completed" '$(WaitHandle)'

Projects

Using Cfoo, it is possible to split your templates up into logical components that will
combined to form your CloudFormation template.

First, create a directory in your project directory called modules. For each module,
create some Cfoo templates defining the different parts of your app. Your project
structure will look like this:

my-web-app
└── modules
    ├── application
    │   ├── app_servers.yml
    │   ├── database.yml
    │   └── public_load_balancer.yml
    ├── instances
    │   └── instance_mappings.yml
    └── network
        ├── bastion.yml
        ├── cfn_user.yml
        ├── dns.yml
        ├── nat.yml
        ├── private_subnet.yml
        ├── public_subnet.yml
        └── vpc.yml

Use Cfoo to generate your project’s CloudFormation template

$ cfoo > web-app.template.json

Shortcuts

Cfoo allows you to simplify CloudFormation intrinsic function
references using its own shorthand

Reference

CloudFormation: { "Ref" : "InstanceType" }

Cfoo Shortcut: $(InstanceType)

Mapping Reference

CloudFormation: { "FindInMap" : [ "SubnetConfig", "VPC", "CIDR" ] }

Cfoo Shortcut: $(SubnetConfig[VPC][CIDR])

Attribute Reference

CloudFormation: { "Fn::GetAtt" : [ "Ec2Instance", "PublicIp" ] }

Cfoo Shortcut: $(Ec2Instance[PublicIp])

Embedded Reference

CloudFormation: { "Fn::Join" : [ "", [{"Ref" : "HostedZone"}, "." ]]}

Cfoo Shortcut: $(HostedZone).

YAML Types

Cfoo gives you the option of using YAML custom data-types where it helps to make your templates easier to read.

Reference

CloudFormation:

{ "Ref" : "InstanceType" }

YAML Type:

!Ref InstanceType

Mapping Reference

CloudFormation:

{ "FindInMap" : [ "SubnetConfig", "VPC", "CIDR" ] }

YAML Type:

!FindInMap [ SubnetConfig, VPC, CIDR ]

Attribute Reference

CloudFormation:

{ "Fn::GetAtt" : [ "Ec2Instance", "PublicIp" ] }

YAML Type:

!GetAtt [ Ec2Instance, PublicIp ]

Base64 String

CloudFormation:

{ "Fn::Base64" : "#!/bin/bash\necho 'Running script...'" }

YAML Type:

!Base64 "#!/bin/bash\necho 'running script...'"

Alternative YAML Type:

!Base64 |
    #!/bin/bash
    echo 'running script...'

Condition Function

CloudFormation:

{ "Fn::Equals": [ "sg-mysggroup", {"Ref": "ASecurityGroup"} ] },

YAML Type:

!Equals [ "sg-mysggroup", $(ASecurityGroup) ]

Goals

Primary Goals

Cfoo aims to let developers simplify CloudFormation templates by:

• allowing them to write templates in YAML
• providing an expression language to simplify CF Ref/Attr/etc expressions
• allowing templates to be split up into logical components (to simplify and share)

Secondary Goals

Cfoo also aims (subject to Primary Goals) to:

• allow inclusion existing JSON templates (so you don’t have to switch all at once)

Non-goals

Cfoo does not (yet) aim to:

• provide commandline utilities for interacting directly with CloudFormation (it just generates the templates for now)
• resolve/validate references (the CloudFormation API already does this)

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Make your changes (with tests please)
4. Commit your changes (git commit -am 'Add some feature')
5. Push to the branch (git push origin my-new-feature)
6. Create new Pull Request