【Lambda】NFC 名刺のアクセスカウンターを Lambda Function URL + DynamoDB で作る

import boto3
import os
from datetime import datetime, timezone, timedelta

dynamodb = boto3.resource("dynamodb")
table = dynamodb.Table(os.environ["TABLE_NAME"])

JST = timezone(timedelta(hours=9))
ALLOWED_REFS = {"nfc", "qr"}  # ホワイトリスト方式。想定外の値は other に振り分け


def handler(event, context):
    method = event.get("requestContext", {}).get("http", {}).get("method", "")
    if method != "POST":
        # ブラウザで URL を直接開いた場合（GET）にカウントされないようにする
        return {"statusCode": 405}

    params = event.get("queryStringParameters") or {}
    ref = params.get("ref", "other")
    if ref not in ALLOWED_REFS:
        ref = "other"

    today = datetime.now(JST).strftime("%Y-%m-%d")

    # ADD はアイテムが無ければ自動作成 → 事前の PutItem 不要
    table.update_item(
        Key={"ref": ref, "date": today},
        UpdateExpression="ADD #c :inc",
        ExpressionAttributeNames={"#c": "count"},
        ExpressionAttributeValues={":inc": 1},
    )

    return {"statusCode": 204}

import * as cdk from 'aws-cdk-lib';
import * as dynamodb from 'aws-cdk-lib/aws-dynamodb';
import * as lambda from 'aws-cdk-lib/aws-lambda';
import { Construct } from 'constructs';

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

    const table = new dynamodb.Table(this, 'VisitorCounterTable', {
      partitionKey: { name: 'ref', type: dynamodb.AttributeType.STRING },
      sortKey: { name: 'date', type: dynamodb.AttributeType.STRING },
      billingMode: dynamodb.BillingMode.PAY_PER_REQUEST, // 低トラフィック向けオンデマンド課金
      removalPolicy: cdk.RemovalPolicy.DESTROY, // スタック削除時にテーブルも削除
    });

    const fn = new lambda.Function(this, 'VisitorCounterFunction', {
      runtime: lambda.Runtime.PYTHON_3_12,
      handler: 'index.handler',
      code: lambda.Code.fromAsset('lambda/visitor-counter'),
      environment: { TABLE_NAME: table.tableName },
      timeout: cdk.Duration.seconds(10),
    });

    table.grantWriteData(fn); // CDK が最小限の IAM ポリシーを自動生成

    const fnUrl = fn.addFunctionUrl({
      authType: lambda.FunctionUrlAuthType.NONE,
      cors: { allowedOrigins: ['*'], allowedMethods: [lambda.HttpMethod.POST] },
    });

    new cdk.CfnOutput(this, 'CounterUrl', { value: fnUrl.url });
  }
}

// CloudFront Functions (viewer-request)
function handler(event) {
    var request = event.request;
    var uri = request.uri;

    if (uri === '/nfc' || uri === '/qr') {
        request.uri = '/profile-website.html';
    }

    return request;
}

<script>
    (function() {
        var COUNTER_ENDPOINT = 'https://xxxxx.lambda-url.us-east-1.on.aws/';
        var path = window.location.pathname;
        var ref = path === '/nfc' ? 'nfc' : path === '/qr' ? 'qr' : 'other';
        navigator.sendBeacon(COUNTER_ENDPOINT + '?ref=' + encodeURIComponent(ref));
    })();
</script>

def handler(event, context):
    method = event.get("requestContext", {}).get("http", {}).get("method", "")

    if method == "GET":
        return dashboard()  # DynamoDB を scan して集計表の HTML を返す

    if method != "POST":
        # ブラウザで URL を直接開いた場合（GET）にカウントされないようにする
        return {"statusCode": 405}

    ...

table.grantReadWriteData(fn); // scan（読み取り）も必要になったため書き込み専用から変更