Streamline Your Serverless Workflow: A Guide to LocalStack and VS Code Testing
Developing serverless applications offers incredible scalability and flexibility, but it often comes with a significant challenge: a slow and cumbersome development loop. Constantly deploying to a live AWS environment to test minor changes is time-consuming, costly, and can lead to the dreaded “it works on my machine” problem when collaborating with a team.
Fortunately, there’s a powerful solution that brings the cloud to your local machine. By integrating LocalStack with Visual Studio Code, you can create a robust, efficient, and cost-free environment for building and testing your serverless applications. This guide will walk you through setting up a seamless local workflow that will dramatically accelerate your development process.
Why Test Serverless Applications Locally?
Before diving into the setup, it’s essential to understand the benefits of a local-first approach to serverless development.
- Faster Feedback Loops: Instead of waiting minutes for a cloud deployment, you can deploy and test your functions in seconds. This rapid iteration is crucial for productivity.
- Significant Cost Reduction: Running tests and debugging locally means you aren’t incurring AWS costs for Lambda invocations, API Gateway requests, or data transfer during the development phase.
- Offline Development: With a local AWS environment, you can continue to build and test your application even without an internet connection.
- Consistent and Isolated Environments: Every developer on the team can run an identical, isolated stack on their machine, eliminating environment-related bugs and simplifying onboarding.
What is LocalStack?
LocalStack is a fully functional local AWS cloud stack that allows you to develop and test your cloud-native applications entirely on your local machine. It runs in a Docker container and provides a high-fidelity emulation of essential AWS services, including:
- AWS Lambda
- Amazon API Gateway
- Amazon S3
- Amazon DynamoDB
- Amazon SQS & SNS
- And many more…
By emulating these services locally, LocalStack allows you to use the same Infrastructure as Code (IaC) tools—like the Serverless Framework or AWS SAM—to deploy and test your application without ever touching a live AWS account.
Setting Up Your Local Development Environment
Getting started is straightforward. Here’s what you need to build a powerful local serverless testing environment.
Prerequisites
Ensure you have the following tools installed on your system:
- Docker Desktop: LocalStack runs inside a Docker container.
- Visual Studio Code: The editor where we’ll integrate everything.
- Node.js & npm: Required for the Serverless Framework and sample Lambda functions.
- AWS CLI: Useful for interacting with your local services.
Step 1: Install and Run LocalStack
The easiest way to get LocalStack running is through its CLI. First, install it using pip:
pip install localstack
Once installed, simply start the LocalStack container:
localstack start -d
This command will pull the necessary Docker image and start all the core cloud services in the background. You now have a mock AWS cloud running on localhost.
Step 2: Integrate with the Serverless Framework
The Serverless Framework is a popular tool for defining and deploying serverless applications. To make it work with our local environment, we need the serverless-localstack plugin.
First, install the plugin in your project directory:
npm install serverless-localstack --save-dev
Next, update your serverless.yml file to include the plugin and configure it for a local stage:
plugins:
- serverless-localstack
custom:
localstack:
stages:
- local
host: http://localhost
edgePort: 4566
autostart: false
This configuration tells the Serverless Framework that whenever you deploy to the local stage, it should direct all AWS API calls to your running LocalStack container instead of the real AWS cloud.
Deploying and Testing Your First Local Function
With the environment set up, you can now deploy a function and test it instantly.
Define Your Function: Create a simple handler in a file like
handler.jsand define the corresponding function and HTTP event in yourserverless.yml.Deploy Locally: Run the deployment command, specifying the local stage:
sls deploy --stage localYou will see the framework output showing that it’s creating resources like Lambda functions and API Gateway endpoints on your local instance. The output will include a local endpoint URL for your function.
Invoke and Test: You can now test your function in several ways:
- Use the
invoke localcommand:sls invoke local -f yourFunctionName --stage local - Use a tool like
curlor Postman to send a request to the local API Gateway endpoint provided after deployment.
- Use the
Any changes you make to your code can be re-deployed and tested in seconds, not minutes.
Supercharging Your Workflow with VS Code Extensions
The true power of this setup comes from integrating it directly into VS Code. The AWS Toolkit for VS Code is an essential extension for this.
While it’s designed to connect to AWS, you can easily configure it to point to LocalStack.
- Install the AWS Toolkit from the VS Code Marketplace.
- Configure a Local Endpoint: In your VS Code
settings.jsonfile, add a custom endpoint configuration that points to your LocalStack container. This allows the toolkit’s resource explorer to connect to your local environment. - Explore Local Resources: Once configured, you can use the AWS Toolkit sidebar to view and interact with your locally deployed resources. You can browse S3 buckets, view Lambda functions, and even invoke them directly from within your editor, streamlining your debugging process even further.
Best Practices for Local Serverless Development
To get the most out of this workflow, keep these security and efficiency tips in mind:
- Maintain Parity with Production: Use the same Infrastructure as Code (IaC) definitions for both your local and cloud environments. This ensures your tests accurately reflect how your application will behave in production.
- Integrate into Your CI/CD Pipeline: Local testing is the first line of defense. Use LocalStack in your continuous integration pipeline to run automated tests before deploying to a shared staging or production environment.
- Security is Still Key: Even though you are working locally, maintain good security hygiene. Avoid hardcoding credentials or sensitive information. Use environment variables or other standard secrets management practices, just as you would in a live environment.
By adopting a local-first testing strategy with LocalStack and VS Code, you can build, test, and debug serverless applications with greater speed, confidence, and control, ultimately leading to higher-quality software delivered faster.
Source: https://aws.amazon.com/blogs/aws/accelerate-serverless-testing-with-localstack-integration-in-vs-code-ide/
