Migrating a Native JAVA REST API to a Serverless Architecture with the Lambada Framework for AWS

NOTE: Newer guidance on the topic of migrating Java based applications to AWS Lambda can be found here: Replatforming Java based applications to AWS Lambda.

This is a guest post by Çağatay Gürtürk, the creator of the Lambada framework

Serverless computing has become a hot topics since AWS Lambda and Amazon API Gateway started to offer an elegant way to build and deploy REST APIs without needing to maintain 24/7 running servers and infrastructure, with attractive pricing models.

Being the first language offered by Lambda, Node.JS seems to have the most online resources and tools but it is also possible to write Lambda functions natively with Java and Python. Java is especially interesting as a language because of its maturity, large community, and available codebase. With Lambda and Java, it is even possible to apply enterprise patterns and frameworks such as Spring, as well as all the best practices we used to apply in the Java world.

In order to make development for Lambda in Java easier, I started Lambada Framework as an open source project. It is a little, but powerful, open source project in beta stage that lets developers create a new serverless API in AWS infrastructure or migrate an existing one.

Lambada Framework accomplishes this target by implementing the most common JAX-RS annotations and providing a Maven plugin to deploy easily to the AWS cloud. Briefly, JAX-RS is a standard annotation set which can be used to map regular Java methods to HTTP paths and methods. For instance, you can look at the following method:

@GET
@Path("/helloworld/{id}")
public Response indexEndpoint(@PathParam int id) {
    return Response.status(200).entity("Hello world: " + id).build();
}

This is a very lean method marked with @GET and @Path annotations, which mean that this method is called when a GET request comes to URLs in “/helloworld/{id}” format, with theid parameter as an argument. Finally, it returns a Response object within this method with a 200 response code and text content. As you can see, these annotations offer a seamless way to define a REST API and map different resources to Java methods.

JAX-RS annotations on their own do not mean so much and they do not have any effect out-of-the-box. To make these annotations work, a JAX-RS implementation framework should be added to the project. This framework would scan all the JAX-RS annotations in the project and create a server and routing table to respond to HTTP requests correctly. While Jersey is one such reference implementation, and the most popular one, there are also other implementations of JAX-RS, such as RESTEasy and Apache CXF. You are free to choose any of them and your controller methods always stay same, thanks to standard annotations.

Lambada Framework is a JAX-RS implementation but different from the others: instead of running a web server, it scans the JAX-RS annotations at build time and populates Lambda functions and the API Gateway definitions using them.

This means that if you already marked your controller methods with JAX-RS annotations and used a framework like Jersey or RestEasy, you can easily switch to serverless architecture with very little modifications in your code. You would have to change only your build mechanism and replace your preferred JAX-RS implementation with Lambada Framework.

In the following example, you see how to deploy a very basic REST API to Lambda.

1. First, clone the example project to your local directory:
   git clone https://github.com/lambadaframework/lambadaframework-boilerplate

1. This project has a pom.xml file with some configuration options. You must change the deployment.bucket option; other changes are up to you. The Lambada Framework creates this bucket in your account if it does not exists and it uses that bucket during your project’s lifetime. S3 bucket names are global and must be unique, so you must pick a name which is not taken by any one else.
2. Make sure that the default AWS profile installed in your system has administrator privileges, or at least the following IAM policy:

     {
            "Version": "2012-10-17",
            "Statement": [
                {
                    "Effect": "Allow",
                    "Action": [
                        "cloudformation:*",
                        "s3:*",
                        "lambda:*",
                        "execute-api:*",
                        "apigateway:*",
                        "iam:*",
                        "ec2:DescribeSecurityGroups",
                        "ec2:DescribeVpcs",
                        "ec2:DescribeSubnets"
                    ],
                    "Resource": [
                        "*"
                    ]
                }
            ]
        }

1. Now you are all set. In the root directory of your project, fire the following command:mvn deploy

Your project compiles to a fat JAR with all its dependencies and is deployed to Lambda. After the JAR file is on the S3 bucket, Lambada scans that for supported JAX-RS annotations in your code and creates the necessary API Gateway endpoints. At the end of the process, the URL of your API is printed on the screen. You can navigate to this URL and explore your API using the AWS Management Console to see which resources and methods are created.

Lambada Framework is under development and support for missing JAX-RS annotations are being added. Follow the Lambada Framework GitHub page for the newest features and feel free to submit any issue or contributions.

Happy serverless computing!