Messiah-AWS

Messiah-AWS is a simple wrapper that makes it easy to write JSON-powered APIs on top of AWS Lambda and API Gateway in a generic fashion in Go, using the recently announced official Go support. It's a thin - very thin - layer of abstraction over the aws-lambda-go SDK that makes it easy to cleanly adapt existing or new Go APIs to deploy onto Lambda and API Gateway, in an adaptable way that avoids vendor lock-in.

No more hacks, no more weird proxies, no AWS-specific magic, just straight up Go and everything that's great about that.

There's a detailed tutorial on how to implement Messiah here.

Why use Messiah?

Messiah-AWS makes working with Lambda, API Gateway, and Go much simpler. Namely, it helps you implement good Go patterns like encapsulation and composition into your microservice API endpoint handlers by providing a couple simple abstractions over the aws-sdk-go package.

Rather than building a request handler that speaks ctx context.Context, request events.APIGatewayProxyRequest and passing that function into lambda.Start(), you'll pass a generic Handle function that speaks req Messiah.Request and res Messiah.Response into Messiah.GetLambdaHandler(handler) and pass that into Messiah.Start.

Like so, from the example:

func (handler StatusHandler) Handle(req Messiah.Request) interface{} {
	status := handler.Status

	body := map[string]interface{}{
		"status":  status,
		"request": req,
	}

	res := Messiah.Response{
		StatusCode:   200,
		ResponseData: body,
	}

	return res
}

func main() {
	status := config.GetStatus()

	handler := StatusHandler{
		Status: status,
	}

	Messiah.Start(handler)
}

This will automagically pass/parse the generic Messiah-AWS handler into lambda.Start(). This makes it much easier to adapt Messiah to any other backend - including, theoretically, a simple HTTP serer - without changing your code. You'd just replace "Messiah" with another package that implements Messiah's generic Request, Response types on your generic Messiah handlers.

Specifically, use Messiah-AWS and the Messiah pattern if:

You want to separate implementation from business logic and avoid vendor lock in

Rather than being tied into Lambda, Messiah's simple layer of abstraction gives you generic methods to access generic request and response data, and a provider-agnostic messiah.Start() method (which simply calls lambda.Start. Switching to a new serverless deployment engine would simply entail adapting Messiah to speak the API of your provider - while it wouldn't be instant, it would be much less work to do so than if you were tied directly into the events.APIGatewayProxyResponse and events.APIGatewayProxyRequest structs and lambda.Start methods.

Since Messiah-AWS simply abstracts over the aws-lambda-go package, migrating from Lambda to a different provider -- or even a traditional HTTP server -- would simply be a matter of building a different package that implements Messiah's generic Response, Request types and Messiah.Start methods, and updating your import paths to point to this forked version of Messiah-AWS.

That being said, Messiah uses embedded types in it's Request and Response structs, so you still have access to all that stuff through Messiah's Request and Response types. However, talking to those embedded types directly may make it harder to migrate from Lambda to your provider of choice.

You want to adapt an existing Go API to run on Lambda

If you already have a clean Go API tied into ServeHTTP(res http.ResponseWriter, req *http.Request), adapting your handlers to speak to Messiah instead should be very simple. It's a matter of simply modifying your handlers slightly - instead of ServeHTTP(res http.ResponseWriter, req *http.Request), you'll change that to something like Handle(req Messiah.Request) and instead of json.NewEncoder(res).Encode(apiResponse), you'll simply do something like:

res := Messiah.Response{
    StatusCode:   200,
    ResponseData: body,
}

return res

You like JSON, but don't like (un)encoding it

One of the other small layers of abstraction on top of the native aws-lambda-go package is native support for marshalling and unmarshalling JSON. If it can, Messiah automatically unmarshalls the request body into a Request.RequestData map and marshalls Response.ResponseData into a JSON response body.

But never fear - if it can't marshall Response.ResponseData into JSON, it'll try and output the body as a string.

FAQ

Why is it called Messiah?

There's were a lot of use of the symbol "handler" while building this, and calling it Handel would've been too confusing.

What's the license?

MIT

How do I run an API that's built on top of Messiah locally?

You wait until @mhart gets done adding Go support to docker-lambda so that aws-sam-local works with Go. Last I heard it's coming "Real Soon Now™ 😊."

In the meantime, your tests should be good enough to verify functionality.

This is awesome and I want more?

I live in west LA and happy to chat about your AWS/Serverless needs. Take a peak at my resume or contact me at [email protected].

Acknowledgements

Special thanks to @mnaughto for helping me through the initial prototype of this (and the name), and for our company, HBK Engineering, for sponsoring the development time. We do lots of cool mapping things - if you'd like to hear more about our team, feel free to reach out.