How to use DynamoDB in your serverless app

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

Requirements

• Node.js 16 or later
• We’ll be using TypeScript
• An AWS account with the AWS CLI configured locally

Create an SST app

Let’s start by creating an SST app.

$ npx create-sst@latest --template=base/example rest-api-dynamodb
$ cd rest-api-dynamodb
$ npm install

By default, our app will be deployed to the us-east-1 AWS region. This can be changed in the sst.config.ts in your project root.

import { SSTConfig } from "sst";

export default {
  config(_input) {
    return {
      name: "rest-api-dynamodb",
      region: "us-east-1",
    };
  },
} satisfies SSTConfig;

Project layout

An SST app is made up of two parts.

1. stacks/ — App Infrastructure

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

2. packages/functions/ — App Code

   The code that’s run when your API is invoked is placed in the packages/functions/ 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 stacks/ExampleStack.ts with the following.

import { Api, ReactStaticSite, StackContext, Table } from "sst/constructs";

export function ExampleStack({ stack }: StackContext) {
  // Create the table
  const table = new Table(stack, "Counter", {
    fields: {
      counter: "string",
    },
    primaryIndex: { partitionKey: "counter" },
  });
}

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

Setting up the API

Now let’s add the API.

Add this below the Table definition in stacks/ExampleStack.ts.

// Create the HTTP API
const api = new Api(stack, "Api", {
  defaults: {
    function: {
      // Bind the table name to our API
      bind: [table],
    },
  },
  routes: {
    "POST /": "packages/functions/src/lambda.main",
  },
});

// Show the URLs in the output
stack.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 packages/functions/src/lambda.ts will get invoked.

We’ll also bind our table to our API. It allows our API to access (read and write) the table we just created.

Reading from our table

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

Replace packages/functions/src/lambda.ts with the following.

import { DynamoDB } from "aws-sdk";
import { Table } from "sst/node/table";

const dynamoDb = new DynamoDB.DocumentClient();

export async function main() {
  const getParams = {
    // Get the table name from the environment variable
    TableName: Table.Counter.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 package in the packages/functions/ folder.

$ 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.

$ npm run dev

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-ExampleStack: deploying...

 ✅  dev-rest-api-dynamodb-ExampleStack


Stack dev-rest-api-dynamodb-ExampleStack
  Status: deployed
  Outputs:
    ApiEndpoint: https://u3nnmgdigh.execute-api.us-east-1.amazonaws.com

The ApiEndpoint is the API we just created.

Let’s test our endpoint with the SST Console. The SST Console is a web based dashboard to manage your SST apps. Learn more about it in our docs.

Go to the API tab and click Send button to send a POST request.

Note, The API explorer lets you make HTTP requests to any of the routes in your Api construct. Set the headers, query params, request body, and view the function logs with the response.

You should see a 0 in the response body.

Writing to our table

Now let’s update our table with the hits.

Add this above the return statement in packages/functions/src/lambda.ts.

const putParams = {
  TableName: Table.Counter.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 clicks row’s tally column with the increased count.

And if you head over to your API explorer and hit the Send button again, you should see the count increase!

Also let’s go to the DynamoDB tab in the SST Console and check that the value has been updated in the table.

Note, The DynamoDB explorer allows you to query the DynamoDB tables in the Table constructs in your app. You can scan the table, query specific keys, create and edit items.

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!