AWS GoFormation

GoFormation is a Go library for working with AWS CloudFormation / AWS Serverless Application Model (SAM) templates.

• AWS GoFormation
  • Main features
  • Installation
  • Usage
    • Marshalling CloudFormation/SAM described with Go structs, into YAML/JSON
    • Unmarshalling CloudFormation YAML/JSON into Go structs
  • Updating CloudFormation / SAM Resources in GoFormation
  • Advanced
    • AWS CloudFormation Intrinsic Functions
      • Resolving References (Ref)
  • Versioning
  • Contributing

Main features

• Describe AWS CloudFormation and AWS SAM templates as Go objects (structs), and then turn it into JSON/YAML.
• Parse JSON/YAML AWS CloudFormation and AWS SAM templates and turn them into Go structs.
• Strongly typed Go structs generated for every AWS CloudFormation and AWS SAM resource.
• Automatically generated, from the published AWS CloudFormation Resource Specification.

Installation

As with other Go libraries, GoFormation can be installed with go get.

$ go get github.com/awslabs/goformation/v7

Usage

Marshalling CloudFormation/SAM described with Go structs, into YAML/JSON

Below is an example of building a CloudFormation template programmatically, then outputting the resulting JSON

package main

import (
	"fmt"
	"strconv"
	"time"

	"github.com/awslabs/goformation/v7/cloudformation"
	"github.com/awslabs/goformation/v7/cloudformation/sns"
)

func main() {

	// Create a new CloudFormation template
	template := cloudformation.NewTemplate()

	// Create an Amazon SNS topic, with a unique name based off the current timestamp
	template.Resources["MyTopic"] = &sns.Topic{
		TopicName: cloudformation.String("my-topic-" + strconv.FormatInt(time.Now().Unix(), 10)),
	}

	// Create a subscription, connected to our topic, that forwards notifications to an email address
	template.Resources["MyTopicSubscription"] = &sns.Subscription{
		TopicArn: cloudformation.Ref("MyTopic"),
		Protocol: "email",
		Endpoint: cloudformation.String("[email protected]"),
	}

	// Let's see the JSON AWS CloudFormation template
	j, err := template.JSON()
	if err != nil {
		fmt.Printf("Failed to generate JSON: %s\n", err)
	} else {
		fmt.Printf("%s\n", string(j))
	}

	// and also the YAML AWS CloudFormation template
	y, err := template.YAML()
	if err != nil {
		fmt.Printf("Failed to generate YAML: %s\n", err)
	} else {
		fmt.Printf("%s\n", string(y))
	}

}

Would output the following JSON template:

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Resources": {
    "MyTopic": {
      "Properties": {
        "TopicName": "my-topic-1536878058"
      },
      "Type": "AWS::SNS::Topic"
    },
    "MyTopicSubscription": {
      "Properties": {
        "Endpoint": "[email protected]",
        "Protocol": "email",
        "TopicArn": {
          "Ref": "MyTopic"
        }
      },
      "Type": "AWS::SNS::Subscription"
    }
  }
}

...and the following YAML template:

AWSTemplateFormatVersion: 2010-09-09
Resources:
  MyTopic:
    Properties:
      TopicName: my-topic-1536878058
    Type: AWS::SNS::Topic
  MyTopicSubscription:
    Properties:
      Endpoint: [email protected]
      Protocol: email
      TopicArn:
        Ref: MyTopic
    Type: AWS::SNS::Subscription

When creating templates, you can use the following convenience functions to use AWS CloudFormation Intrinsics:

• cloudformation.Ref(logicalName string)
• cloudformation.GetAtt(logicalName string, attribute string)
• cloudformation.ImportValue(name string)
• cloudformation.Base64(input string)
• cloudformation.CIDR(ipBlock, count, cidrBits string)
• cloudformation.FindInMap(mapName, topLevelKey, secondLevelKey string)
• cloudformation.GetAZs(region string)
• cloudformation.Join(delimiter string, values []string)
• cloudformation.Select(index string, list []string)
• cloudformation.Split(delimiter, source string)
• cloudformation.Sub(value string)
• And(conditions []string)
• Equals(value1, value2 string)
• If(value, ifEqual, ifNotEqual string)
• Not(conditions []string)
• Or(conditions []string)

Unmarshalling CloudFormation YAML/JSON into Go structs

GoFormation also works the other way - parsing JSON/YAML CloudFormation/SAM templates into Go structs.

package main

import (
	"log"

	"github.com/awslabs/goformation/v7"
)

func main() {

	// Open a template from file (can be JSON or YAML)
	template, err := goformation.Open("template.yaml")
	if err != nil {
		log.Fatalf("There was an error processing the template: %s", err)
	}

	// You can extract all resources of a certain type
	// Each AWS CloudFormation resource is a strongly typed struct
	functions := template.GetAllServerlessFunctionResources()
	for name, function := range functions {

		// E.g. Found a AWS::Serverless::Function named GetHelloWorld (runtime: nodejs6.10)
		log.Printf("Found a %s named %s (runtime: %s)\n", function.AWSCloudFormationType(), name, function.Runtime)

	}

	// You can also search for specific resources by their logicalId
	search := "GetHelloWorld"
	function, err := template.GetServerlessFunctionWithName(search)
	if err != nil {
		log.Fatalf("Function not found")
	}

	// E.g. Found a AWS::Serverless::Function named GetHelloWorld (runtime: nodejs6.10)
	log.Printf("Found a %s named %s (runtime: %s)\n", function.AWSCloudFormationType(), search, function.Runtime)

}

Updating CloudFormation / SAM Resources in GoFormation

AWS GoFormation contains automatically generated Go structs for every CloudFormation/SAM resource, located in the cloudformation/ directory. These can be generated, from the latest AWS CloudFormation Resource Specification published for us-east-1 by just running go generate:

$ go generate

Generated 587 AWS CloudFormation resources from specification v1.4.2
Generated 17 AWS SAM resources from specification v2016-10-31
Generated JSON Schema: schema/cloudformation.schema.json

The GoFormation build pipeline automatically checks for any updated AWS CloudFormation resources on a daily basis, and creates a pull request against this repository if any are found.

Advanced

AWS CloudFormation Intrinsic Functions

The following AWS CloudFormation Intrinsic Functions are supported in GoFormation:

• Fn::Base64
• Fn::FindInMap
• Fn::Join
• Fn::Select
• Fn::Split
• Fn::Sub
• Ref
• Fn::And
• Fn::Equals
• Fn::If
• Fn::Not
• Fn::Or
• Fn::GetAtt
• Fn::GetAZs
• Fn::ImportValue

Any unsupported intrinsic functions will return nil.

Resolving References (Ref)

When converting a YAML/JSON template to go, the intrinsic 'Ref' function as implemented will resolve all of the pseudo parameters such as AWS::AccountId with their default value as listed on the page.

If a reference is not a pseudo parameter, GoFormation will try to resolve it within the AWS CloudFormation template. Currently, this implementation only searches for Parameters with a name that matches the ref, and returns the Default if it has one.

Versioning

This library is automatically versioned and tagged using semantic-release.

Contributing

Contributions and feedback are welcome! Proposals and pull requests will be considered and responded to. For more information, see the CONTRIBUTING file.