In this example we will look at how to use DynamoDB in our serverless app using Serverless Stack Toolkit (SST). We’ll be creating a simple hit counter.

Requirements

Create an SST app

Let’s start by creating an SST app.

$ npx create-serverless-stack@latest rest-api-dynamodb
$ cd rest-api-dynamodb

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": "rest-api-dynamodb",
  "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 DynamoDB

Amazon DynamoDB is a reliable and highly-performant NoSQL database that can be configured as a true serverless database. Meaning that it’ll scale up and down automatically. And you won’t get charged if you are not using it.

Replace the lib/MyStack.js with the following.

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

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

    // Create the table
    const table = new sst.Table(this, "Counter", {
      fields: {
        counter: sst.TableFieldType.STRING,
      },
      primaryIndex: { partitionKey: "counter" },
    });
  }
}

This creates a serverless DynamoDB table using sst.Table. It has a primary key called counter. Our table is going to look something like this:

counter tally
hits 123

Setting up the API

Now let’s add the API.

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

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

// Allow the API to access the table
api.attachPermissions([table]);

// Show API endpoint in output
new cdk.CfnOutput(this, "ApiEndpoint", {
  value: api.httpApi.apiEndpoint,
});

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

We also pass in the name of our DynamoDB table to our API as an environment variable called tableName. And we allow our API to access (read and write) the table instance we just created.

Reading from our table

Now in our function, we’ll start by reading from our DynamoDB table.

Replace src/lambda.js with the following.

import AWS from "aws-sdk";

const dynamoDb = new AWS.DynamoDB.DocumentClient();

export async function main() {
  const getParams = {
    // Get the table name from the environment variable
    TableName: process.env.tableName,
    // Get the row where the counter is called "hits"
    Key: {
      counter: "hits",
    },
  };
  const results = await dynamoDb.get(getParams).promise();

  // If there is a row, then get the value of the
  // column called "tally"
  let count = results.Item ? results.Item.tally : 0;

  return {
    statusCode: 200,
    body: count,
  };
}

We make a get call to our DynamoDB table and get the value of a row where the counter column has the value hits. Since, we haven’t written to this column yet, we are going to just return 0.

Let’s install the aws-sdk.

$ npm install aws-sdk

And let’s test what we have so far.

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-rest-api-dynamodb-my-stack: deploying...

 ✅  dev-rest-api-dynamodb-my-stack (no changes)


Stack dev-rest-api-dynamodb-my-stack
  Status: no changes
  Outputs:
    ApiEndpoint: https://u3nnmgdigh.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://u3nnmgdigh.execute-api.us-east-1.amazonaws.com

You should see a 0 printed out.

Writing to our table

Now let’s update our table with the hits.

Add this above the return statement in src/lambda.js.

const putParams = {
  TableName: process.env.tableName,
  Key: {
    counter: "hits",
  },
  // Update the "tally" column
  UpdateExpression: "SET tally = :count",
  ExpressionAttributeValues: {
    // Increase the count
    ":count": ++count,
  },
};
await dynamoDb.update(putParams).promise();

Here we are updating the hits row’s tally column with the increased count.

And now if you head over to your terminal and make a request to our API. You’ll notice the count increase!

$ curl -X POST https://u3nnmgdigh.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 hit counter. In another example, we’ll expand on this to create a CRUD API. Check out the repo below for the code we used in this example. And leave a comment if you have any questions!