In this example we will look at how to use SQS to create a queue in our serverless app using Serverless Stack (SST). We’ll be creating a simple queue system.

Requirements

Create an SST app

Let’s start by creating an SST app.

$ npx create-serverless-stack@latest queue
$ cd queue

By default our app will be deployed to an environment (or stage) called dev and the us-east-1 AWS region. This can be changed in the sst.json in your project root.

{
  "name": "queue",
  "stage": "dev",
  "region": "us-east-1"
}

Project layout

An SST app is made up of two parts.

  1. lib/ — App Infrastructure

    The code that describes the infrastructure of your serverless app is placed in the lib/ directory of your project. SST uses AWS CDK, to create the infrastructure.

  2. src/ — App Code

    The code that’s run when your API is invoked is placed in the src/ directory of your project.

Adding SQS Queue

Amazon SQS is a reliable and high-throughput message queuing service. You are charged based on the number of API requests made to SQS. And you won’t get charged if you are not using it.

Replace the lib/MyStack.js with the following.

import * as sst from "@serverless-stack/resources";

export default class MyStack extends sst.Stack {
  constructor(scope, id, props) {
    super(scope, id, props);

    // Create Queue
    const queue = new sst.Queue(this, "Queue", {
      consumer: "src/consumer.main",
    });
  }
}

This creates an SQS queue using sst.Queue. And it has a consumer that polls for messages from the queue. The consumer function will run when it has polled 1 or more messages.

Setting up the API

Now let’s add the API.

Add this below the sst.Queue definition in lib/MyStack.js.

// Create the HTTP API
const api = new sst.Api(this, "Api", {
  defaultFunctionProps: {
    // Pass in the queue to our API
    environment: {
      queueUrl: queue.sqsQueue.queueUrl,
    },
  },
  routes: {
    "POST /": "src/lambda.main",
  },
});

// Allow the API to publish to the queue
api.attachPermissions([queue]);

// Show the API endpoint in the output
this.addOutputs({
  ApiEndpoint: api.url,
});

Our API simply has one endpoint (the root). When we make a POST request to this endpoint the Lambda function called main in src/main.js will get invoked.

We also pass in the url of our SQS queue to our API as an environment variable called queueUrl. And we allow our API to send messages to the queue we just created.

Adding function code

We will create two functions, one for handling the API request, and one for the consumer.

Replace the src/lambda.js with the following.

export async function main() {
  console.log("Message queued!");
  return {
    statusCode: 200,
    body: JSON.stringify({ status: "successful" }),
  };
}

Add a src/consumer.js.

export async function main() {
  console.log("Message processed!");
  return {};
}

Now let’s test our new API.

Starting your dev environment

SST features a Live Lambda Development environment that allows you to work on your serverless apps live.

$ npx sst start

The first time you run this command it’ll take a couple of minutes to deploy your app and a debug stack to power the Live Lambda Development environment.

===============
 Deploying app
===============

Preparing your SST app
Transpiling source
Linting source
Deploying stacks
dev-queue-my-stack: deploying...

 ✅  dev-queue-my-stack (no changes)


Stack dev-queue-my-stack
  Status: deployed
  Outputs:
    ApiEndpoint: https://i8ia1epqnh.execute-api.us-east-1.amazonaws.com

The ApiEndpoint is the API we just created. Let’s test our endpoint. Run the following in your terminal.

$ curl -X POST https://i8ia1epqnh.execute-api.us-east-1.amazonaws.com

You should see {status: 'successful'} printed out. And if you head back to the debugger, you should see Item queued!.

Sending message to our queue

Now let’s send a message to our queue.

Replace the src/lambda.js with the following.

import AWS from "aws-sdk";

const sqs = new AWS.SQS();

export async function main() {
  // Send a message to queue
  await sqs
    .sendMessage({
      // Get the queue url from the environment variable
      QueueUrl: process.env.queueUrl,
      MessageBody: JSON.stringify({ ordered: true }),
    })
    .promise();

  console.log("Message queued!");

  return {
    statusCode: 200,
    body: JSON.stringify({ status: "successful" }),
  };
}

Here we are getting the queue url from the environment variable, and then sending a message to it.

Let’s install the aws-sdk.

$ npm install aws-sdk

And now if you head over to your terminal and make a request to our API. You’ll notice in the debug logs that our consumer is called. And you should see Message processed! being printed out.

$ curl -X POST https://i8ia1epqnh.execute-api.us-east-1.amazonaws.com

Deploying to prod

To wrap things up we’ll deploy our app to prod.

$ npx sst deploy --stage prod

This allows us to separate our environments, so when we are working in dev, it doesn’t break the API for our users.

Cleaning up

Finally, you can remove the resources created in this example using the following commands.

$ npx sst remove
$ npx sst remove --stage prod

Conclusion

And that’s it! We’ve got a completely serverless queue system. Check out the repo below for the code we used in this example. And leave a comment if you have any questions!