aws-cfn-resources gem

CloudFormation is ideal for creating resources on AWS. Each resource in a CloudFormation template is described using a Logical_Resource description. During stack creation, physical resources are instantiated from these logical resource descriptions. When stack creation is complete, we are left with a mapping of (known) Logical_Resource_Ids to (AWS generated) Physical_Resource_Ids.

By mixing methods into AWS::CloudFormation::Stack, the aws-cfn-resources gem is meant to make it easy to retrieve these physical resources in the form of AWS::* objects.

It also makes sense to go the other direction, and to retrieve the AWS::CloudFormation::Stack responsible for creating a particular resource. So this gem provides a stack method for most AWS taggable resources.

• gem install aws-cfn-resources
• require aws-cfn-resources

You need to provide your AWS security credentials and choose a default region.

AWS.config(access_key_id: '...', secret_access_key: '...', region: 'us-east-1')

You can also specify these values via ENV:

export AWS_ACCESS_KEY_ID='...'
export AWS_SECRET_ACCESS_KEY='...'
export AWS_REGION='us-east-1'

Create a stack object

cfn = AWS::CloudFormation.new
stack = cfn.stacks['myStack']

Example 1

Given a CloudFormation template snippet for a stack named "myStack":

Resources: {
  "myWebInstance" : {
    "Type" : "AWS::EC2::Instance",
    "Properties" : {
      "..."
    }
  },
  "myDbInstance" : {
    "Type" : "AWS::EC2::Instance",
    "Properties" : {
      "..."
    }
  }
}

Return an AWS::EC2::Instance object for "myWebInstance"

require 'aws-cfn-resources'
cfn = AWS::CloudFormation.new

stack = cfn.stacks['myStack']
instance = stack.instance('myWebInstance')
#=> <AWS::EC2::Instance id:i-abc12345>

Return a hash containting all AWS::EC2::Instance resource types created by the cfn stack

stack = cfn.stacks['myStack']
instances = stack.instances
#=> {:myWebInstance=><AWS::EC2::Instance id:i-abc12345>,:myDbInstance=><AWS::EC2::Instance id:i-def67890>}

Example 2

Given a Cloudformation template snippet for a stack named "VpcCreator":

Resources: {
  "myVpc" : {
    "Type" : "AWS::EC2::VPC",
    "Properties" : {
      "..."
    }
  },
  "WebSubnet" : {
    "Type" : "AWS::EC2::Subnet",
    "Properties" : {
      "..."
    }
  }
}

Return VPC and Subnet names to be used as parameter values in a dependent template

vpc_stack = cfn.stacks['VpcCreator']
vpc_id = vpc_stack.vpc('myVpc').id
web_subnet_id = vpc_stack.subnet('WebSubnet').id

resp = cfn.client.create_stack({stack_name: 'webStack', template_body: web_template, parameters: [{ParameterKey: "VpcId", ParameterValue: vpc_id}, {ParameterKey: "WebSubnetId", ParameterValue: web_subnet_id}] })

Cloudformation snippet for web.template used to create "webStack":

Parameters : {
  "VpcId" : {
    "..."
  },
  "WebSubnetId" : {
    "..."
  }
}

Example 3

Return AWS::CloudFormation::Stack that created a specific AWS resource

ec2 = AWS::EC2.new
web_instance = ec2.instances['i-abc12345']
vpc = ec2.vpcs['vpc-def67890']

web_instance.stack
#=> <AWS::CloudFormation::Stack stack_name:webStack> 

vpc.stack
#=> <AWS::CloudFormation::Stack stack_name:VpcCreator>

Example 4 Calling resource methods for non-exist resources will return nil

require 'aws-cfn-resources'
cfn = AWS::CloudFormation.new

stack = cfn.stacks['myStack']
instance = stack.instance('foo')
#=> nil

Calling #stack method on resources NOT created by CloudFormation or not 'taggable' will also return nil

WARNING: Running Rspec will create stacks and real AWS resources (that cost real money!!) Make sure to delete these stacks when testing is complete.

Note: Test tasks are only meant to be deployed to the 'us-east-1' region for now. Making the test templates multi-region is on the roadmap.

You can test with:

rake EC2=true AS=true #test EC2 and AutoScaling resources
rake ALL=true #test all resources

## pass one or more of the following arguments to Rake to indicate which resource(s) to test
AS=true #test autoscaling resources
CW=true #test cloudwatch alarm resource
EC2=true #test ec2 resources
ELB=true #test elastic load balancer resource
IAM=true #test IAM resources
RDS=true #test db_instanace resource
S3=true #test S3 bucket resource

## or test all
ALL=true #test all resources