Building Your First Serverless Service With AWS Lambda Functions

Many developers have some familiarity with AWS Lambda functions. While relatively easy to set up, navigating the vast AWS ecosystem can be challenging. The sheer number of components makes it difficult to grasp the bigger picture and integrate Lambda functions smoothly into a standard web application.

The Serverless Framework simplifies this process considerably. It streamlines the creation, deployment, and—most importantly—the integration of Lambda functions into web applications. While its capabilities extend far beyond this, this article focuses on these core aspects. This introduction hopefully sparks your interest to explore Serverless's broader functionalities. If you're new to Lambda, consider reviewing this AWS introductory guide first.

The quick start guide provides the best instructions for initial installation and setup. Following it, you should be operational within 5-10 minutes, even if you need to create an AWS account.

Your First Serverless Service

Before diving into advanced features like file uploads and S3 buckets, let's create a basic Lambda function, connect it to an HTTP endpoint, and invoke it from an existing web application. The function won't perform any complex tasks, but it effectively demonstrates the ease of use of the Serverless Framework.

Begin by creating your service. In your web application (using create-react-app is a quick way to start a new one), create a directory for your services (e.g., a lambda folder). Navigate to this directory in your terminal and run:

sls create -t aws-nodejs --path hello-world

This creates a hello-world directory. Let's examine its contents.

handler.js contains an asynchronous function that returns a message. You could deploy this Lambda function immediately using sls deploy, making it invokable. However, let's first make it accessible via the web.

Manual AWS configuration would involve setting up an AWS API Gateway endpoint and stage, then configuring it to proxy to your Lambda. Serverless handles all this with minimal configuration.

Still in the hello-world directory, open serverless.yaml.

The configuration file includes boilerplate for common setups. Uncomment the HTTP entries and specify a more descriptive path:

functions:
  hello:
    handler: handler.hello
    events:
      - http:
        path: msg
        method: get

That's it. Serverless manages the underlying complexities.

CORS Configuration

To invoke the function from front-end JavaScript using the Fetch API, CORS configuration is necessary. This section outlines the process.

Add cors: true below the configuration:

functions:
  hello:
    handler: handler.hello
    events:
      - http:
        path: msg
        method: get
        cors: true

This configures CORS on the API endpoint, enabling cross-origin communication.

CORS Lambda Adjustment

While the HTTP endpoint is CORS-enabled, the Lambda function must return the appropriate headers. Let's automate this by modifying handler.js:

const CorsResponse = obj => ({
  statusCode: 200,
  headers: {
    "Access-Control-Allow-Origin": "*",
    "Access-Control-Allow-Headers": "*",
    "Access-Control-Allow-Methods": "*"
  },
  body: JSON.stringify(obj)
});

module.exports.hello = async event => {
  return CorsResponse("HELLO, WORLD!");
};

Now, the Lambda function's response is processed through this function.

Run sls deploy from the hello-world directory to deploy the Lambda function.

The sls info command provides the function's URL, eliminating the need to manually locate it in the AWS console. The URL will resemble:

<code>https://6xpmc3g0ch.execute-api.us-east-1.amazonaws.com/dev/msg</code>

Invoking the Function

Now, let's invoke the function from a web application using Fetch:

fetch("https://6xpmc3g0ch.execute-api.us-east-1.amazonaws.com/dev/msg")
  .then(resp => resp.json())
  .then(resp => {
    console.log(resp);
  });

The message should appear in the browser's developer console.

Let's repeat this process, creating a more practical function: a Lambda that resizes images and uploads them to an S3 bucket. Instead of triggering on S3 uploads, the user uploads directly to the Lambda, eliminating the need for client-side AWS SDK resources.

Building a Practical Lambda

Let's create a new service (e.g., cover-art):

sls create -t aws-nodejs --path cover-art

Add the HTTP endpoint path (POST method for file uploads) and enable CORS:

events:
  - http:
    path: upload
    method: post
    cors: true

Grant the Lambda access to your S3 bucket(s) by uncommenting and modifying the iamRoleStatements section in serverless.yaml:

iamRoleStatements:
  - Effect: "Allow"
    Action:
      - "s3:*"
    Resource: ["arn:aws:s3:::your-bucket-name/*"]

Configure the API Gateway to accept multipart/form-data:

provider:
  name: aws
  runtime: nodejs12.x
  apiGateway:
    binaryMediaTypes:
      - 'multipart/form-data'

Rename the function in serverless.yaml and handler.js to upload.

Implementing the Code

Install required packages:

npm i jimp uuid lambda-multipart-parser

Implement an S3 upload helper function and the main upload function in handler.js (the complete code is too extensive to include here, but it's available in the original prompt).

Use a library like react-dropzone on the client-side to handle file uploads (example code provided in the original prompt).

Optional: Bundling

Bundling your code reduces deployment size and improves performance. Install serverless-webpack:

npm i serverless-webpack --save-dev

Add it to serverless.yaml:

plugins:
  - serverless-webpack

Create webpack.config.js (configuration provided in the original prompt). Redeploy to utilize webpack.

Conclusion

The Serverless Framework significantly simplifies the development and deployment of AWS Lambda functions. This introduction provides a foundation for further exploration of its capabilities. The resources mentioned in the original prompt offer valuable learning opportunities for deeper understanding.

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