UPDATE: We have developed Upstash Rate Limiting SDK. We recommend it with Upstash Redis. In this tutorial, we will throttle AWS Lambda functions using Serverless Redis based on the client’s IP address. See code. See demo.

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1 Serverless Project Setup

If you do not have it already, install serverless framework via: npm install -g serverless In any folder run serverless as below: 
>> serverless

Serverless: No project detected. Do you want to create a new one? Yes
Serverless: What do you want to make? AWS Node.js
Serverless: What do you want to call this project? serverless-rate-limiting

Project successfully created in 'serverless-rate-limiting' folder.

You can monitor, troubleshoot, and test your new service with a free Serverless account.

Serverless: Would you like to enable this? No
You can run the “serverless” command again if you change your mind later.
See Using AWS SAM, if you prefer AWS SAM over Serverless Framework.
Inside the project folder create a node project with the command: 
npm init
Then install the redis client and rate limiting libraries with: 
npm install ioredis async-ratelimiter request-ip
Update the serverless.yml as below. Copy your Redis URL from console and replace below: 
service: serverless-rate-limiting
frameworkVersion: "2"
provider:
  name: aws
  runtime: nodejs12.x
  lambdaHashingVersion: 20201221
functions:
  hello:
    handler: handler.hello
    events:
      - httpApi:
          path: /hello
          method: get
For the best performance choose the same region for your Lambda function and Upstash database.

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2 Create a Redis (Upstash) Database

Create a database from Upstash console

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3 Code

Edit handler.js and replace your REDIS_URL below.
This example uses ioredis, you can copy the connection string from the Node tab in the console.
const RateLimiter = require("async-ratelimiter");
const Redis = require("ioredis");
const { getClientIp } = require("request-ip");

const rateLimiter = new RateLimiter({
  db: new Redis("YOUR_REDIS_URL"),
  max: 1,
  duration: 5_000,
});

module.exports.hello = async (event) => {
  const clientIp = getClientIp(event) || "NA";
  const limit = await rateLimiter.get({ id: clientIp });
  if (!limit.remaining) {
    return {
      statusCode: 429,
      body: JSON.stringify({
        message: "Sorry, you are rate limited. Wait for 5 seconds",
      }),
    };
  }

  return {
    statusCode: 200,
    body: JSON.stringify({
      message: "hello!",
    }),
  };
};
Above, we have configured the rate limiting to accept 1 request from the same IP address in 5 seconds.

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4 Deploy and Try the API

Deploy your functions with: 
serverless deploy
The command will deploy the function and show the endpoint url. Click to the endpoint url. If you refresh your page, you will see that your request is throttled.