GitHub Repository

You can find the project source code on GitHub.

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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.