AWS Lambda Go API Proxy

aws-lambda-go-api-proxy makes it easy to run Go APIs written with frameworks such as Gin with AWS Lambda and Amazon API Gateway.

Getting started

Install required dependencies.

# First, install the Lambda go libraries.
$ go get github.com/aws/aws-lambda-go/events
$ go get github.com/aws/aws-lambda-go/lambda

# Next, install the core library.
$ go get github.com/awslabs/aws-lambda-go-api-proxy/...

Standard library

To use with the standard library, the httpadaptor.New function takes in a http.Handler. The ProxyWithContent method on the httpadapter.HandlerAdapter can then be used as a Lambda handler.

package main

import (
	"io"
	"net/http"

	"github.com/aws/aws-lambda-go/lambda"
	"github.com/awslabs/aws-lambda-go-api-proxy/httpadapter"
)

func main() {
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		io.WriteString(w, "Hello")
	})

	lambda.Start(httpadapter.New(http.DefaultServeMux).ProxyWithContext)
}

Gin

To use with the Gin framework, following the instructions from the Lambda documentation, declare a Handler method for the main package.

Declare a ginadapter.GinLambda object in the global scope, and initialize it in the init function, adding all API methods.

The ProxyWithContext method is then used to translate requests and responses.

package main

import (
	"log"
	"context"

	"github.com/aws/aws-lambda-go/events"
	"github.com/aws/aws-lambda-go/lambda"
	"github.com/awslabs/aws-lambda-go-api-proxy/gin"
	"github.com/gin-gonic/gin"
)

var ginLambda *ginadapter.GinLambda

func init() {
	// stdout and stderr are sent to AWS CloudWatch Logs
	log.Printf("Gin cold start")
	r := gin.Default()
	r.GET("/ping", func(c *gin.Context) {
		c.JSON(200, gin.H{
			"message": "pong",
		})
	})

	ginLambda = ginadapter.New(r)
}

func Handler(ctx context.Context, req events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {
	// If no name is provided in the HTTP request body, throw an error
	return ginLambda.ProxyWithContext(ctx, req)
}

func main() {
	lambda.Start(Handler)
}

Other frameworks

This package also supports Negroni, GorillaMux, and plain old HandlerFunc - take a look at the code in their respective sub-directories. All packages implement the Proxy method exactly like our Gin sample above.

Deploying the sample

We have included a SAM template with our sample application. You can use the AWS CLI to quickly deploy the application in your AWS account.

First, build the sample application by running make from the aws-lambda-go-api-proxy directory.

$ cd aws-lambda-go-api-proxy
$ make

The make process should generate a main.zip file in the sample folder. You can now use the AWS CLI to prepare the deployment for AWS Lambda and Amazon API Gateway.

$ cd sample
$ aws cloudformation package --template-file sam.yaml --output-template-file output-sam.yaml --s3-bucket YOUR_DEPLOYMENT_BUCKET
$ aws cloudformation deploy --template-file output-sam.yaml --stack-name YOUR_STACK_NAME --capabilities CAPABILITY_IAM

Using the CloudFormation console, you can find the URL for the newly created API endpoint in the Outputs tab of the sample stack - it looks sample like this: https://xxxxxxxxx.execute-api.xx-xxxx-x.amazonaws.com/Prod/pets. Open a browser window and try to call the URL.

API Gateway context and stage variables

The RequestAccessor object, and therefore GinLambda, automatically marshals the API Gateway request context and stage variables objects and stores them in custom headers in the request: X-GinLambda-ApiGw-Context and X-GinLambda-ApiGw-StageVars. While you could manually unmarshal the json content into the events.APIGatewayProxyRequestContext and map[string]string objects, the library exports two utility methods to give you easy access to the data.

The gateway context, stage variables and lambda runtime variables are automatically populate to the context.

// the methods are available in your instance of the GinLambda
// object and receive the context
apiGwContext := ginLambda.GetAPIGatewayContextFromContext(ctx)
apiGwStageVars := ginLambda.GetStageVarsFromContext(ctx)
runtimeContext := ginLambda.GetRuntimeContextFromContext(ctx)

// you can access the properties of the context directly
log.Println(apiGwContext.RequestID)
log.Println(apiGwContext.Stage)
log.Println(runtimeContext.InvokedFunctionArn)


// stage variables are stored in a map[string]string
stageVarValue := apiGwStageVars["MyStageVar"]

Supporting other frameworks

The aws-lambda-go-api-proxy, alongside the various adapters, declares a core package. The core package, contains utility methods and interfaces to translate API Gateway proxy events into Go's default http.Request and http.ResponseWriter objects.

You can see that the ginlambda.go file extends the RequestAccessor struct defined in the request.go file. RequestAccessor gives you access to the ProxyEventToHTTPRequest() method.

The GinLambda object is initialized with an instance of gin.Engine. gin.Engine implements methods defined in the http.Handler interface.

The Proxy method of the GinLambda object simply receives the events.APIGatewayProxyRequest object and uses the ProxyEventToHTTPRequest() method to convert it into an http.Request object. Next, it creates a new ProxyResponseWriter object (defined in the response.go) file and passes both request and response writer to the ServeHTTP method of the gin.Engine.

The ProxyResponseWriter exports a method called GetProxyResponse() to generate an events.APIGatewayProxyResponse object from the data written to the response writer.

Support for frameworks other than Gin can rely on the same methods from the core package and swap the gin.Engine object for the relevant framework's object.

License

This library is licensed under the Apache 2.0 License.