GitHub Repository

You can find the project source code on GitHub.
 In this tutorial, we will implement a Serverless API using AWS Lambda and we will deploy it using AWS CDK. We will use Typescript as the CDK language. It will be a view counter where we keep the state in Redis.

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What is AWS CDK?

AWS CDK is an interesting project which allows you to provision and deploy AWS infrastructure with code. Currently TypeScript, JavaScript, Python, Java, C#/.Net and Go are supported. You can compare AWS CDK with following technologies:
  • AWS CloudFormation
  • AWS SAM
  • Serverless Framework
The above projects allows you to set up the infrastructure with configuration files (yaml, json) while with AWS CDK, you set up the resources with code. For more information about CDK see the related AWS Docs.

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Prerequisites

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Project Setup

Create and navigate to a directory named counter-cdk. The CDK CLI uses this directory name to name things in your CDK code, so if you decide to use a different name, don’t forget to make the appropriate changes when applying this tutorial. 
mkdir counter-cdk && cd counter-cdk
Initialize a new CDK project. 
cdk init app --language typescript
Install @upstash/redis. 
npm install @upstash/redis

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Counter Function Setup

Create /api/counter.ts.
/api/counter.ts
import { Redis } from '@upstash/redis';

const redis = Redis.fromEnv();

export const handler = async function() {
    const count = await redis.incr("counter");
    return {
        statusCode: 200,
        body: JSON.stringify('Counter: ' + count),
    };
};

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Counter Stack Setup

Update /lib/counter-cdk-stack.ts.
/lib/counter-cdk-stack.ts
import * as cdk from 'aws-cdk-lib';
import { Construct } from 'constructs';
import * as lambda from 'aws-cdk-lib/aws-lambda';
import * as nodejs from 'aws-cdk-lib/aws-lambda-nodejs';

export class CounterCdkStack extends cdk.Stack {
  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const counterFunction = new nodejs.NodejsFunction(this, 'CounterFunction', {
      entry: 'api/counter.ts',
      handler: 'handler',
      runtime: lambda.Runtime.NODEJS_20_X,
      environment: {
        UPSTASH_REDIS_REST_URL: process.env.UPSTASH_REDIS_REST_URL || '',
        UPSTASH_REDIS_REST_TOKEN: process.env.UPSTASH_REDIS_REST_TOKEN || '',
      },
      bundling: {
        format: nodejs.OutputFormat.ESM,
        target: "node20",
        nodeModules: ['@upstash/redis'],
      },
    });

    const counterFunctionUrl = counterFunction.addFunctionUrl({
      authType: lambda.FunctionUrlAuthType.NONE,
    });

    new cdk.CfnOutput(this, "counterFunctionUrlOutput", {
      value: counterFunctionUrl.url,
    })
  }
}

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Database Setup

Create a Redis database using Upstash Console or Upstash CLI and export UPSTASH_REDIS_REST_URL and UPSTASH_REDIS_REST_TOKEN to your environment. 
export UPSTASH_REDIS_REST_URL=<YOUR_URL>
export UPSTASH_REDIS_REST_TOKEN=<YOUR_TOKEN>

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Deploy

Run in the top folder: 
cdk synth
cdk bootstrap
cdk deploy
Visit the output URL.