The first part of this series introduced you to the AWS Lambda Go API Proxy, and how it's framework/package specific adapter implementations (for gorilla/mux, echo and net/http) allows you to run existing Go applications as AWS Lambda functions fronted by Amazon API Gateway. If you haven't already, I encourage you to take a look at it in order to get a basic understanding of the AWS Lambda Go API Proxy.

The AWS Lambda Go API Proxy also supports Gin, is one of the most popular Go web frameworks! This follow-up blog post will demonstrate how take an existing URL shortener service written using the Gin framework, and run it as a serverless AWS Lambda function. Instead of using AWS SAM, we will change things up a bit and use the AWS CDK to deploy the solution.

The code is available on GitHub

How does the Gin adapter for AWS Lambda Go API Proxy work?

The aws-lambda-go-api-proxy package makes it possible to run Go APIs written using Gin, thanks to the framework specific adapter implementations.

To understand this, let's look into the main.go file of the Lambda function:

var ginLambda *ginadapter.GinLambda

func init() {
    r := gin.Default()

    r.POST("/app", CreateShortURL)
    r.GET("/app/:shortcode", GetShortURL)
    r.DELETE("/app/:shortcode", DeleteShortURL)
    r.PUT("/app/:shortcode", UpdateStatus)

    ginLambda = ginadapter.New(r)
}

func Handler(ctx context.Context, req events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {
    return ginLambda.ProxyWithContext(ctx, req)
}

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

• In the init function:
  • We use gin.Default() to create a gin.Engine object with the Logger and Recovery middleware already attached.
  • We create routes by associating a gin.HandlerFunc with each HTTP method and path using the POST, GET, DELETE and PUT methods of the gin.Engine object.
  • ginadapter.New function takes this *gin.Engine object and returns a ginadapter.GinLambda.
• In the Handler implementation:
  • The Proxy (or ProxyWithContext) method of the ginadapter.GinLambda object receives the events.APIGatewayProxyRequest, converts it into a http.Request object, and sends it to the gin.Engine for routing.
  • It returns a proxy response object (events.APIGatewayProxyResponse) generated from the data written to the response writer (http.ResponseWriter).

Application overview

The sample application presented in this blog is a trimmed down version of bit.ly or other solutions you may have used. It uses Amazon DynamoDB for persistence and exposes HTTP endpoints to access the application (basic CRUD operations).

Although we will not be discussing the application code in detail, it's important to understand the basic structure. Here is the package structure for the URL shortener application (in the function directory):

.
├── db
│   └── db.go
├── go.mod
├── go.sum
├── handler.go
├── main.go

• The db package contains code to interact with DynamoDB.
• The handler.go file has the implementation for the HTTP methods.
• The main.go file creates the Gin engine with the routes and ginadapter.GinLambda object to proxy requests and responses.

It's time to deploy the URL shortener application and give it a go!

Prerequisites

Before you proceed, make sure you have the Go programming language (v1.18 or higher) and AWS CDK installed.

Clone the GitHub repository and change to the right directory:

git clone https://github.com/build-on-aws/golang-gin-app-on-aws-lambda

cd golang-gin-app-on-aws-lambda

Use AWS CDK to deploy the solution

AWS CDK is a framework that lets you define your cloud infrastructure as code in one of its supported programming and provision it through AWS CloudFormation. In this case, we will be using the Go bindings for AWS CDK

You can refer to the code in the cdk directory.

To start the deployment, invoke the cdk deploy command. You will see a list of resources that will be created and will need to provide your confirmation to proceed.

cd cdk

cdk deploy

# output

Bundling asset LambdaGolangProxyAPIDemoStack/gin-go-lambda-function/Code/Stage...

✨  Synthesis time: 5.94s

This deployment will make potentially sensitive changes according to your current security approval level (--require-approval broadening).
Please confirm you intend to make the following modifications:

//.... omitted

Do you wish to deploy these changes (y/n)? y

Enter y to start creating the AWS resources required for the application. This will start creating the AWS resources required for our application.

If you want to see the AWS CloudFormation template which will be used behind the scenes, run cdk synth and check the cdk.out folder

You can keep track of the progress in the terminal or navigate to AWS console: CloudFormation > Stacks > LambdaGolangProxyAPIDemoStack

Once all the resources are created, you can try out the application. You should have:

• An API Gateway REST API.
• A Lambda function.
• A DynamoDB table to store application data.
• And a few other components (like IAM roles etc.).

Try the URL shortener application

You will need the API Gateway endpoint to invoke with the application - it's available as part of the stack output (in the terminal or the Outputs tab in the AWS CloudFormation console for your stack). It should look something like this - https://foobarbazl.execute-api.us-east-1.amazonaws.com/prod/

1. Start by generating a short code

To generate a short code, you need to pass the original URL in the payload body as part of a HTTP POST request (for e.g. https://abhirockzz.github.io/)

# e.g. export URL_SHORTENER_APP_URL=https://foobarbazl.execute-api.us-east-1.amazonaws.com/prod/app
export URL_SHORTENER_APP_URL=<replace with API Gateway endpoint above>/app

# invoke the endpoint to create short code
curl -i -X POST -d '{"url":"https://abhirockzz.github.io/"}' $URL_SHORTENER_APP_URL
curl -i -X POST -d '{"url":"https://abhishek1987.medium.com/"}' $URL_SHORTENER_APP_URL
curl -i -X POST -d '{"url":"https://dzone.com/users/456870/abhirockzz.html"}' $URL_SHORTENER_APP_URL

If all goes well, you should get a HTTP 201 along with the short code in the HTTP response (as a JSON payload).

HTTP/2 201 
content-type: text/plain; charset=utf-8
content-length: 25
apigw-requestid: VTzPsgmSoAMESdA=

{"short_code":"1ee3ad1b"}

Check the DynamoDB table to verify records with the short code with the corresponding URL.

2. Access the URL using the short code

The access link will have the following format - <URL_SHORTENER_APP_URL>/app/<generated short code> for e.g. https://8zbqx074rl.execute-api.us-east-1.amazonaws.com/prod/app/4b824fad

Once you navigate to the link using a browser, you will be automatically redirected to the original URL that you had specified. To better understand what's going on behind the scenes, try accessing the same URL with curl

curl -i $URL_SHORTENER_APP_URL/app/1ee3ad1b

You should get a HTTP 302 response (Found) and the URL redirection happens due to the Location HTTP header which has the original URL.

# some of the headers omitted for brevity
HTTP/2 302 
content-type: application/json
content-length: 0
location: https://abhirockzz.github.io/
....

3. Disable a short code

You can disable (and enable) the short codes. The original URL will only be accessible if the association is in active state.

To disable a short code:

export URL_SHORTENER_APP_URL=<replace with API Gateway endpoint above>/app

curl -i -X PUT -d '{"active": false}'  -H 'Content-Type: application/json' $URL_SHORTENER_APP_URL/3626fb51

This is a HTTP PUT request with a JSON payload that specifies the status (false in this case refers to disable action) along with the short code which is a path parameter to the API Gateway endpoint. If all works well, you should see an HTTP 204 (No Content) response.

Check the corresponding record in DynamoDB - the active attribute should have switched to false.

4. Delete a short code

export URL_SHORTENER_APP_URL=<replace with API Gateway endpoint above>/app

curl -i -X DELETE $URL_SHORTENER_APP_URL/<short code>

Just like in the case of update, you should get a HTTP 204 response. But this time, the respective DynamoDB record will be deleted.

We covered the basic operations for the URL shortener application. As an exercise, try out the following scenarios and check the response(s):

• Access a disabled URL.
• Enable a disabled URL (use {"active": true}).
• Access an invalid short code (that does not exist).

Clean up

Once you're done, to delete all the services, simply use:

cdk destroy

Conclusion

In this blog post you took a URL shortener application built using the Gin framework and deployed it as a Lambda function. Although this was a simple example, the same approach can be used to deploy more complex applications. As long as you have reasonable separation of concerns and your application is modular, most of the work will involve refactoring parts of the logic (main.go in this case) to wire up the Gin router (gin.Engine) to a Lambda function handler (entry point) by using the adapter implementation for Gin.

Happy Building!