Serverless computing has revolutionized how we build and deploy scalable applications. By leveraging serverless functions, developers can focus on writing code without managing the infrastructure, making it more efficient and cost-effective. However, testing serverless functions locally is crucial for ensuring quality, accelerating development cycles, and debugging before deploying to the cloud. In this guide, we’ll walk through how to set up a serverless application and test it locally.
Step 1: Install Required Tools
Before you start building your serverless application, you need to install a few essential tools.
AWS CLI
The AWS Command Line Interface (CLI) is necessary for managing AWS resources such as Lambda functions, API Gateway, DynamoDB, and more. It allows you to interact with AWS services from your terminal.
To install AWS CLI, run the following command:
pip install awscli
Serverless Framework
The Serverless Framework is a popular open-source tool that helps developers build, deploy, and manage serverless applications. It simplifies the creation of serverless functions, their deployment, and the integration with other services.
To install the Serverless Framework, use npm:
npm install -g serverless
Step 2: Set Up Your Project
Once you have the tools installed, you can create a new serverless project. This will set up the structure for your serverless application.
Run the following command to scaffold a new service:
serverless
This command will prompt you to choose a template. Select the AWS - Node.js - HTTP API template. This template is suitable for building serverless applications with API Gateway and Lambda functions using Node.js.
After choosing the template, you will be asked to provide a name for your service. Pick a name that is relevant to your project.
Optionally, you can log in or sign up for the Serverless Dashboard. This is a management tool provided by Serverless Framework that helps you monitor, deploy, and track your service.
Your project structure will look something like this:
- serverless.yml: This file contains the configuration for your service, including the functions, events, and resources.
- handler.js: This file contains the serverless function code.
Step 3: Install Serverless Offline Plugin
To test your serverless functions locally before deploying to AWS, you can use the serverless-offline plugin. This plugin simulates AWS API Gateway and Lambda locally, allowing you to invoke your functions and test endpoints as if they were running on the cloud.
To install the serverless-offline plugin, run the following command:
npm install serverless-offline
Next, open the serverless.yml file and add the plugin under the plugins section. This will enable the offline capabilities.
Here’s an example of what your serverless.yml file might look like after adding the plugin:
Step 4: Run Locally
With the serverless-offline plugin installed and configured, you can now start the local environment and test your endpoints locally.
To run the local server, use the following command:
serverless offline start
This command will start a local version of API Gateway and Lambda. You can now make HTTP requests to your functions as if they were deployed on AWS, but all operations will be local.
By default, the local server will be available at:
http://localhost:3000
You can open your browser or use a tool like Postman or cURL to test the GET request to the /hello endpoint:
curl http://localhost:3000/hello
This should invoke your Lambda function and return the response defined in your handler.
Conclusion
Setting up serverless applications with local testing capabilities is a powerful approach to ensure fast iteration and quality assurance during development. With tools like AWS CLI, Serverless Framework, and the serverless-offline plugin, you can create serverless functions, test them locally, and ensure they work as expected before deploying to the cloud.
Here’s a quick recap of the steps:
- Install AWS CLI and Serverless Framework.
- Scaffold a new service using Serverless Framework.
- Install the serverless-offline plugin to simulate AWS Lambda and API Gateway locally.
- Run the service locally and test the endpoints.
By following this guide, you can streamline your serverless development process and avoid surprises when deploying to the cloud. Local testing with the serverless-offline plugin allows you to quickly debug and validate your functions, improving your development workflow and reducing the time it takes to get your serverless application into production.