Using CloudFormation

Why use CloudFormation?

Cloud computing allows for application repeatability and redundancy. This means that you can spin up as many virtual machines as you need, but the application configuration only needs to happen when the images are created. CloudFormation takes this concept to the next level: it allows you to configure an entire set of resources (instances, security groups, user roles and policies, and more) in a single JSON template file. Then you can run all with a single command. So, you don't just get machine repeatability, you get environment repeatability. CloudFormation allows you to clone environments in different cloud setups, as well as giving applications the ability to be set up and torn down in a repeatable manner.

How does CloudFormation Work?

CloudFormation manages a set of resources, called a stack, in batch operations (create, update, or delete). Stacks are described in JSON templates, and can be simple, as the following example:

{
  "Resources" : {
    "MyInstance": {
      "Type": "AWS::EC2::Instance",
      "Properties": {
        "ImageId" : "emi-db0b2276"
      }
    }
  }
}

This stack creates a single instance, based on the image with ID emi-db0b2276. However, this stack is not portable because different clouds might have different image IDs.

CloudFormation allows stack customization through user parameters that are passed in at stack creation time. The following is an example of the template above with a user parameter called MyImageId. Changes are in bold.

{
  "Parameters": {
    "MyImageId": {
      "Description":"Image id",
      "Type":"String"
    }
  },
  "Resources" : {
    "MyInstance": {
      "Type": "AWS::EC2::Instance",
      "Properties": {
        "ImageId" : { "Ref" : "MyImageId" }
      }
    }
  }
}

This stack creates a single instance, but the image ID will be required to be passed in using the command line. For example, the following example uses the euform-create-stack command in Euca2ools:

euform-create-stack --template-file template.json -p MyImageId=emi-db0b2276 MyStack

This command passes the parameter MyImageId with value emi-db0b2276 into the stack creation process using the -p flag.

You can also use templates to create multiple resources and associate them with each other. For example, the following template creates an instance with its own security group and ingress rule. Additions are in bold.

{
  "Parameters": {
    "MyImageId": {
      "Description":"Image id",
      "Type":"String"
    }
  },
  "Resources" : {
    "MySecurityGroup": {
      "Type": "AWS::EC2::SecurityGroup",
      "Properties": {
        "GroupDescription" : "Security Group with Ingress Rule for MyInstance",
        "SecurityGroupIngress" : [
          {
            "IpProtocol" : "tcp",
            "FromPort" : "22",
            "ToPort" : "22",
            "CidrIp" : "0.0.0.0/0"
          }
        ]
      }
    },
    "MyInstance": {
      "Type": "AWS::EC2::Instance",
      "Properties": {
        "ImageId" : { "Ref":"MyImageId" },
        "SecurityGroups" : [ 
          { "Ref" : "MySecurityGroup" } 
        ]
      }
    }
  }
}

Templates can be more complicated than the ones shown above, but CloudFormation allows many resources to be deployed in one operation. Resources from most Eucalyptus services are supported.

CloudFormation Requirements

To run CloudFormation on Eucalyptus, you need the following:

• A running Eucalyptus cloud, version 4.0 or later, with at least one Cloud Controller, Node Controller, and Cluster Controller up, running and registered
• At least one active running service of each of the following: CloudWatch, AutoScaling, Load Balancing, Compute, and IAM
• A registered active CloudFormation service

Supported Resources

The following resources are supported by CloudFormation in Eucalyptus.

CloudFormation Registration

To register CloudFormation for your cloud, enter the following command:

euserv-register-service -t CloudFormation -h CLOUD_FORMATION_HOST_IP SVCINSTANCE

For example:

euserv-register-service -t CloudFormation -h 203.0.113.13 cfn

Eucalyptus returns information similar to the following:

Created new partition 'cfn'
 SERVICE    cloudformation   	 cfn  		 cfn http://203.0.113.13:8773/services/
 CloudFormation    arn:euca:bootstrap:cfn:cloudformation:cfn/

The CloudFormation service will be shown when you run euserv-describe-services.

WSDL URL

The service WSDL URL for CloudFormation is of the form:

http://<host-ip>:8773/services/CloudFormation

The services path may not be necessary if DNS is enabled, it may look something like this:

http://cloudformation.g-19-10.autoqa.qa1.eucalyptus-systems.com:8773/

CloudFormation follows the same convention as the other user-facing services.