Environment
Services	Amazon S3, Lambda, DynamoDB, SNS, SQS
Integrations	AWS SDK, OpenTofu, AWS CLI
Categories	Spring Boot, S3 Trigger
Level	Intermediate
Works on	LocalStack v3

The OpenTofu configuration file now randomly generates names for the bucket, in order to avoid conflicts at a global scale on AWS. This name shall be written out to a properties file, which the app will pick up and use for the S3 client. Furthermore, the name is also passed as an environment variable to the Lambda function by OpenTofu, so there's no need to worry about managing it.

This application was created for demonstration purposes to highlight the ease of switching from using actual AWS dependencies to having them emulated on LocalStack for your developer environment . Of course this comes with other advantages, but the first focus point is making the transition.

• Maven 3.8.5 & Java 17
• AWS free tier account
• LocalStack
• Docker - for running LocalStack
• OpenTofu (+ Python pip for tflocal) for creating AWS & LocalStack resources
• npm - for running the frontend app

shipment-list-demo is a Spring Boot application dealing with CRUD operations one can execute on a bunch of shipments that they're allowed to view - think of it like the Post app. The demo consists of a backend and a frontend implementation, using React to display the information. The AWS services involved are:

• S3 for storing pictures
• DynamoDB for the entities
• Lambda function that will validate the pictures, apply a watermark and replace non-compliant files.
• SNS that receives update notifications
• SQS that subscribes to a topic and delivers the messages to the Spring Boot app

We’ll be walking through a few scenarios using the application, and we expect it to maintain the behavior in both production (AWS) and development (LocalStack) environments.

We’ll take advantage of one of the core features of the Spring framework that allows us to bind our beans to different profiles, such as dev, test, and prod. Of course, these beans need to know how to behave in each environment, so they’ll get that information from their designated configuration files, application-prod.yml, and application-dev.yml.

The OpenTofu configuration file will create the needed S3 bucket, the DynamoDB shipment table and populate it with some sample data, the Lambda function that will help with the picture processing (make sure you create the jar), the SQS and SNS which will bring back the notification when the processing is finished.

The following instructions only need to run once, weather you choose to run both cases, on AWS and LocalStack, or just jump straight to LocalStack.

Step into the shipment-picture-lambda-validator module and run mvn clean package shade:shade. This will create an uber-jar by packaging all its dependencies. We'll need this one in the next steps. We can keep the same jar for both running on AWS and LocalStack.

cd into src/main/shipment-list-frontend and run npm install and npm start. This will spin up the React app that can be accessed on localhost:3000. You'll only see the title, as the backend is not running yet to provide the list of shipments.

For running it on Windows, there are some extra requirements , but no worries, it should be straightforward.

After starting the backend, refreshing the React app will fetch a list of shipments. The weight of a shipment is already given, but not the size, that's why we need pictures to understand it better, using the "banana for scale" measuring unit. How else would we know??

Current available actions using the GUI:

• upload a new image
• delete shipment from the list
• create and update shipment are available only via Postman (or any other API platform)

Files that are not pictures will be deleted and the shipment picture will be replaced with a generic icon, because we don't want any trouble.

Now, we don’t have a real production environment because that’s not the point here, but most likely an application like this runs on a container orchestration platform, and all the necessary configs are still provided. Since we’re only simulating a production instance, all the configurations are kept in the application-prod.yml file.

Before getting started, it's important to note that an IAM user, who's credentials will be used, needs to be created with the following policies:

• AmazonS3FullAccess
• AWSLambda_FullAccess
• AmazonDynamoDBFullAccess
• AmazonSNSFullAccess
• AmazonSQSFullAccess
• AWSLambdaExecute
• AmazonS3ObjectLambdaExecutionRolePolicy

For simplicity, we chose to use full access to all the services, so we don't have to add new permissions later on. We will be using the user's credentials and export them as temporary environment variables with the export (set on Windows) command:

$ export AWS_ACCESS_KEY_ID=[your_aws_access_key_id]
$ export AWS_SECRET_ACCESS_KEY=[your_aws_secret_access_key_id]

Make sure you have OpenTofu installed

Under opentofu run:

$ tofu init
$ tofu plan

Once these 2 commands run successfully and no errors occur, it's time to run:

$ tofu apply --auto-approve

If everything finishes successfully, the AWS services should be up and running.

Go back to the root folder and run the backend simply by using

$ mvn spring-boot:run -Dspring-boot.run.profiles=prod

Notice the prod profile is being set via command line arguments.

At localhost:3000 you should now be able to see a list of shipments with standard icons, that means that only the database is populated, the pictures still need to be added from the sample-pictures folder. You can now interact with the application using the React app. All services used in the backend are running on the real AWS cloud.

Before moving on, make sure you clean up your AWS resources by running (also in the opentofu folder):

$ tofu destroy

To switch to using LocalStack instead of AWS services just run docker compose up in the root folder to spin up a Localstack container.

To generate the exact same resources on LocalStack, we need tflocal, a thin wrapper script around the terraform/tofu command line client. tflocal takes care of automatically configuring the local service endpoints, which allows you to easily deploy your unmodified OpenTofu scripts against LocalStack.

tflocal supports both Terraform and OpenTofu. By default, it uses the Terraform binary in your system. To use OpenTofu, all you need to do is customize the TF_CMD environment variable to use the tofu binary:

$ export TF_CMD=tofu

You can install the tflocal command via pip (requires a local Python installation):

$ pip install terraform-local

Once installed, the tflocal command should be available, with the same interface as the tofu command line. Try it out:

$ tflocal --help
Usage: tofu [global options] <subcommand> [args]
...

From here on, it's the same as using AWS. In the opentofu folder, run the cleanup script to get rid of any files that keep track of the resources' state. Then:

$ tflocal init

...
OpenTofu has been successfully initialized!

You may now begin working with OpenTofu. Try running "tofu plan" to see
any changes that are required for your infrastructure. All OpenTofu commands
should now work.

...

$ tflocal plan
$ tflocal apply

We run the exact same commands for the exact same file. We no longer need to pass any environment variables, since the bucket name is generated and passed by OpenTofu.

After that, the Spring Boot application needs to start using the dev profile (make sure you're in the root folder):

$ mvn spring-boot:run -Dspring-boot.run.profiles=dev

Go back to localhost:3000 and a new list will be available; notice that the functionalities of the application have not changed.

There you have it, smooth transition from AWS to Localstack, with no code change. 👍🏻

We appreciate your interest in contributing to our project and are always looking for new ways to improve the developer experience. We welcome feedback, bug reports, and even feature ideas from the community. Please refer to the contributing file for more details on how to get started.