Lifting and shifting a web application to AWS Serverless: Part 1

Lifting and shifting a web application to AWS Serverless: Part 1

Customers migrating to the cloud often want to get the benefits of serverless architecture. But what is the best approach and is it possible? There are many strategies to do a migration, but lift and shift is often the fastest way to get to production with the migrated workload.

You might also wonder if it’s possible to lift and shift an existing application that runs in a traditional environment to serverless. This blog post shows how to do this for a Mongo, Express, React, and Node.js (MERN) stack web app. However, the discussions presented in this post apply to other stacks too.

Why do a lift and shift migration?

Lift and shift, or sometimes referred to as rehosting the application, is moving the application with as few changes as possible. Lift and shift migrations often allow you to get the new workload in production as fast as possible. When migrating to serverless, lift and shift can bring a workload that is not yet in the cloud or in a serverless environment to use managed and serverless services quickly.

Migrating a non-serverless workload to serverless with lift and shift might not bring all the serverless benefits right away, but it enables the development team to refactor, using the strangler pattern, the parts of the application that might benefit from what serverless technologies offer.

Why migrate a web app to serverless?

Web apps hosted in a serverless environment benefit most from the capability of serverless applications to scale automatically and for paying for what you use.

Imagine that you have a personal web app with little traffic. If you are hosting in a serverless environment, you don’t pay a fixed price to have the servers up and running. Your web app has only a few requests and the rest of the time is idle.

This benefit applies to the opposite case. For an owner of a small ecommerce site running on a server, imagine if a social media influencer with millions of followers recommends one of their products. Suddenly, thousands of requests arrive and make the site unavailable. If the site is hosted on a serverless platform, the application will scale to the traffic that it receives.

Requirements for migration

Before starting a migration, it is important to define the nonfunctional requirements that you need the new application to have. These requirements help when you must make architectural decisions during the migration process.

These are the nonfunctional requirements of this migration:

  • Environment that scales to zero and scales up automatically.
  • Pay as little as possible for idle time.
  • Configure as little infrastructure as possible.
  • Automatic high availability of the application.
  • Minimal changes to the original code.

Application overview

This blog post guides you on how to migrate a MERN application. The original application is hosted in two different servers: One contains the Mongo database and another contains the Node/js/Express and ReactJS applications.

This demo application simulates a swag ecommerce site. The database layer stores the products, users, and the purchases history. The server layer takes care of the ecommerce business logic, hosting the product images, and user authentication and authorization. The web layer takes care of all the user interaction and communicates with the server layer using REST APIs.

These are the changes that you must make to migrate to a serverless environment:

The following image shows the proposed solution for the migrated application:

Database migration

The database is already in a MongoDB vanilla container that has all the data for this application. As MongoDB is the database engine for our stack, their recommended solution to migrate to serverless is to use MongoDB Atlas. Atlas provides a database cluster in the cloud that scales automatically and you pay for what you use.

To get started, create a new Atlas cluster, then migrate the data from the existing database to the serverless one. To migrate the data, you can first dump all the content of the database to a dump folder and then restore it to the cloud:

mongodump --uri="mongodb://<localuser>:<localpassword>@localhost:27017"

mongorestore --uri="mongodb+srv://<user>:<password>@<clustername>.debkm.mongodb.net" .

After doing that, your data is now in the cloud. The next step is to change the configuration string in the server to point to the new database. To see this in action, check this video that shows a walkthrough of the migration.

Backend migration

Migrating the Node.js/Express backend is the most challenging of the layers to migrate to a serverless environment, as the server layer is a Node.js application that runs in a server.

One option for this migration is to use AWS Fargate. Fargate is a serverless container service that allows you to scale automatically and you pay as you go. Another option is to use AWS AppRunner, a container service that auto scales and you also pay as you go. However, neither of these options align with our migration requirements, as they don’t scale to zero.

Another option for the lift and shift migration of this Node.js application is to use Lambda with the AWS Lambda Web Adapter. The AWS Lambda Web Adapter is an open-source project that allows you to build web applications with familiar frameworks, like Express.js, Flask, SpringBoot, and run it on Lambda. You can learn more about this project in its GitHub repository.

Using this project, you can create a new Lambda function that has the Express/NodeJS application as the function code. You can lift and shift all the code into the function. If you want a step-by-step tutorial on how to do this, check out this video.

const lambdaAdapterFunction = new Function(this,`${props.stage}-LambdaAdapterFunction`,
            {
                runtime: Runtime.NODEJS_16_X,
                code: Code.fromAsset('backend-app'),
                handler: 'run.sh',
                environment: {
                    AWS_LAMBDA_EXEC_WRAPPER: '/opt/bootstrap',
                    REGION: this.region,
                    ASYNC_INIT: 'true',
                },
                memorySize: 1024,
                layers: [layerLambdaAdapter],
                timeout: Duration.seconds(2),
                tracing: Tracing.ACTIVE,
            }
        );

The next step is to create an HTTP endpoint for the server application. There are three options for doing this: API Gateway, Application Load Balancer (ALB) , or to use Lambda Function URLs. All the options are compatible with Lambda Web Adapter and can solve the challenge for you.

For this demo, choose function URLs, as they are simple to configure and one function URL forwards all routes to the Express server. API Gateway and ALB require more configuration and have separate costs, while the cost of function URLs is included in the Lambda function.

Web app migration

The final layer to migrate is the React application. The best way to migrate the web layer and to adhere to the migration requirements is to use AWS Amplify to host it. AWS Amplify is a fully managed service that provides many features like hosting web applications and managing the CICD process for the web app. It provides client libraries to connect to different AWS resources, and many other features.

Migrating the React application is as simple as creating a new Amplify application in your AWS account and uploading the React application to a code repository like GitHub. This AWS Amplify application is connected to a GitHub branch, and when there is a new commit in this branch, AWS Amplify redeploys the code.

The Amplify application receives configuration parameters like the function URL endpoint (the server URL) using environmental variables.

const amplifyApp = new App(this, `${props.stage}-AmplifyReactShopApp`, {
            sourceCodeProvider: new GitHubSourceCodeProvider({
                owner: config.frontend.owner,
                repository: config.frontend.repository_name,
                oauthToken: SecretValue.secretsManager('github-token'),
            }),
            environmentVariables: {
                REGION: this.region,
                SERVER_URL: props.serverURL,
            },
        });

If you want to see a step-by-step guide on how to make your web layer serverless, you can check this video.

Next steps

However, if you test this migrated app, you will find two issues. The first one is that the user session is not sticky. Every time you log in, you are logged out unexpectedly from the application. The second one is that when you create a new product, you cannot upload new images of that product.

In part two, I analyze each of the problems in detail and find solutions. These issues arise because of the stateless and immutable characteristics of this solution. The next part of this article explains how to solve these issues, also it analyzes costs and performance of the solution.

Conclusion

In this article, you learn if it is possible to migrate a non-serverless web application to a serverless environment without changing much code. You learn different tools that can help you in this process, like the AWS Lambda Web Adaptor and AWS Amplify.

If you want to see the migration in action and learn all the steps for this, there is a playlist that contains all the tutorials for you to follow and learn how this is possible.

For more serverless learning resources, visit Serverless Land.

This content was originally published here.