GitHub - awslabs/goformation: GoFormation is a Go library for working with CloudFormation templates.

AWS GoFormation

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

AWS GoFormation

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("some.email@example.com"),
	}

	// 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": "some.email@example.com",
        "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: some.email@example.com
      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:

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.