GitHub Repository

You can find the project source code on GitHub.

This tutorial shows how to build a serverless API for Page View Counter with Python and Redis. The API will the count page views and show it in JSON format.

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Prerequisites

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Project Setup

Create and navigate to a directory named counter-cdk. 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

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Counter Function Setup

Create a folder named api under lib

mkdir lib/api

Create /lib/api/requirements.txt

/lib/api/requirements.txt
upstash-redis

Create /lib/api/index.py

/lib/api/index.py
from upstash_redis import Redis

redis = Redis.from_env()

def handler(event, context):
    count = redis.incr('counter')
    return {
        'statusCode': 200,
        'body': f'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 path from 'path';

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

    const counterFunction = new lambda.Function(this, 'CounterFunction', {
      code: lambda.Code.fromAsset(path.join(__dirname, 'api'), {
        bundling: {
          image: lambda.Runtime.PYTHON_3_9.bundlingImage,
          command: [
            'bash', '-c',
            'pip install -r requirements.txt -t /asset-output && cp -au . /asset-output'
          ],
        },
      }),
      runtime: lambda.Runtime.PYTHON_3_9,
      handler: 'index.handler',
      environment: {
        UPSTASH_REDIS_REST_URL: process.env.UPSTASH_REDIS_REST_URL || '',
        UPSTASH_REDIS_REST_TOKEN: process.env.UPSTASH_REDIS_REST_TOKEN || '',
      },
    });

    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.

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