How to create a REST API with serverless

In this example we will look at how to create a serverless REST API on AWS using SST.

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
$ cd rest-api
$ 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",
      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.

Setting up our routes

Let’s start by setting up the routes for our API.

Replace the stacks/ExampleStack.ts with the following.

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

export function ExampleStack({ stack }: StackContext) {
  // Create the HTTP API
  const api = new Api(stack, "Api", {
    routes: {
      "GET /notes": "packages/functions/src/list.handler",
      "GET /notes/{id}": "packages/functions/src/get.handler",
      "PUT /notes/{id}": "packages/functions/src/update.handler",
    },
  });

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

We are creating an API here using the Api construct. And we are adding three routes to it.

GET /notes
GET /notes/{id}
PUT /notes/{id}

The first is getting a list of notes. The second is getting a specific note given an id. And the third is updating a note.

Adding function code

For this example, we are not using a database. We’ll look at that in detail in another example. So internally we are just going to get the list of notes from a file.

Let’s add a file that contains our notes in packages/core/src/notes.ts.

export default {
  id1: {
    noteId: "id1",
    userId: "user1",
    createdAt: Date.now(),
    content: "Hello World!",
  },
  id2: {
    noteId: "id2",
    userId: "user2",
    createdAt: Date.now() - 10000,
    content: "Hello Old World! Old note.",
  },
};

Now add the code for our first endpoint.

Getting a list of notes

Add a packages/functions/src/list.ts.

import notes from "@rest-api/core/notes";

export async function handler() {
  return {
    statusCode: 200,
    body: JSON.stringify(notes),
  };
}

Here we are simply converting a list of notes to string, and responding with that in the request body.

Note that this function need to be async to be invoked by AWS Lambda. Even though, in this case we are doing everything synchronously.

Getting a specific note

Add the following to packages/functions/src/get.ts.

import notes from "@rest-api/core/notes";
import { APIGatewayProxyHandlerV2 } from "aws-lambda";

export const handler: APIGatewayProxyHandlerV2 = async (event) => {
  const note = notes[event.pathParameters.id];
  return note
    ? {
        statusCode: 200,
        body: JSON.stringify(note),
      }
    : {
        statusCode: 404,
        body: JSON.stringify({ error: true }),
      };
};

Here we are checking if we have the requested note. If we do, we respond with it. If we don’t, then we respond with a 404 error.

Updating a note

Add the following to packages/functions/src/update.ts.

import notes from "@rest-api/core/notes";
import { APIGatewayProxyHandlerV2 } from "aws-lambda";

export const handler: APIGatewayProxyHandlerV2 = async (event) => {
  const note = notes[event.pathParameters.id];

  if (!note) {
    return {
      statusCode: 404,
      body: JSON.stringify({ error: true }),
    };
  }

  const data = JSON.parse(event.body);

  note.content = data.content;

  return {
    statusCode: 200,
    body: JSON.stringify(note),
  };
};

We first check if the note with the requested id exists. And then we update the content of the note and return it. Of course, we aren’t really saving our changes because we don’t have a database!

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.

$ npm run dev

The first time you run this command it’ll take a couple of minutes to do the following:

1. It’ll bootstrap your AWS environment to use CDK.
2. Deploy a debug stack to power the Live Lambda Development environment.
3. Deploy your app, but replace the functions in the packages/functions/ directory with ones that connect to your local client.
4. Start up a local client.

Once complete, you should see something like this.

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

Preparing your SST app
Transpiling source
Linting source
Deploying stacks
dev-rest-api-ExampleStack: deploying...

 ✅  dev-rest-api-ExampleStack


Stack dev-rest-api-ExampleStack
  Status: deployed
  Outputs:
    ApiEndpoint: https://2q0mwp6r8d.execute-api.us-east-1.amazonaws.com

The ApiEndpoint is the API we just created.

Let’s test our endpoint using the integrated 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 explorer and click the Send button of the GET /notes route to get a list of notes.

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 the list of notes as a JSON string.

To retrieve a specific note, Go to GET /notes/{id} route and in the URL tab enter the id of the note you want to get in the id field and click the Send button to get that note.

Now to update our note, we need to make a PUT request, go to PUT /notes/{id} route.

In the URL tab, enter the id of the note you want to update and in the body tab and enter the below json value and hit Send.

{ "content": "Updating my note" }

This should respond with the updated note.

Making changes

Let’s make a quick change to our API. It would be good if the JSON strings are pretty printed to make them more readable.

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

import notes from "@rest-api/core/notes";

export async function handler() {
  return {
    statusCode: 200,
    body: JSON.stringify(notes, null, "  "),
  };
}

Here we are just adding some spaces to pretty print the JSON.

If you head back to the GET /notes route and hit Send again.

You should see your list of notes in a more readable format.

Deploying your API

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 app for our users.

Once deployed, you should see something like this.

 ✅  prod-rest-api-ExampleStack


Stack prod-rest-api-ExampleStack
  Status: deployed
  Outputs:
    ApiEndpoint: https://ck198mfop1.execute-api.us-east-1.amazonaws.com

Run the below command to open the SST Console in prod stage to test the production endpoint.

npx sst console --stage prod

Go to the API explorer and click Send button of the GET /notes route, to send a GET request.

Cleaning up

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

$ npx sst remove

And to remove the prod environment.

$ npx sst remove --stage prod

Conclusion

And that’s it! You’ve got a brand new serverless API. A local development environment, to test and make changes. And it’s deployed to production as well, so you can share it with your users. Check out the repo below for the code we used in this example. And leave a comment if you have any questions!