Deploying Lambda function: attendanceFunction

Overview

This page describes how to create the attendanceFunction Lambda function.
It is used to query attendance data from DynamoDB based on your Rekognition collection results.

Step 1: Create the Lambda function

  1. In the Lambda console, navigate to Functions.

  2. Choose Create function.

  3. Under Author from scratch:

    • Function name: attendanceFunction
    • Runtime: Node.js 22.x
    • Architecture: x86_64

Other Additional configurations can be left alone.

alt text

  1. Choose Create function.

alt text

Step 2: Add the function code

  1. In the Code tab, replace the default code with the handler from your Amplify project:

alt text

Or copy the handler.js file from:
Amplify/functions/attendanceFunction/handler.js

import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocumentClient, QueryCommand } from "@aws-sdk/lib-dynamodb";

const dynamoClient = new DynamoDBClient({ region: process.env.AWS_REGION });
const ddbDocClient = DynamoDBDocumentClient.from(dynamoClient);

export const handler = async (event) => {
  try {
    const { externalImageId } = event.queryStringParameters || {};

    if (!externalImageId) {
      return {
        statusCode: 400,
        body: JSON.stringify({
          success: false,
          error: "Missing externalImageId",
        }),
      };
    }

    const today = new Date().toISOString().split("T")[0];

    const params = {
      TableName: process.env.DYNAMO_TABLE,
      KeyConditionExpression: "externalImageId = :pk AND checkinDay = :today",
      ExpressionAttributeValues: {
        ":pk": externalImageId,
        ":today": today,
      },
    };

    const result = await ddbDocClient.send(new QueryCommand(params));

    const items = result.Items || [];

    return {
      statusCode: 200,
      body: JSON.stringify({
        success: true,
        count: items.length,
        items,
      }),
    };
  } catch (err) {
    console.error("Error fetching today's check-ins:", err);
    return {
      statusCode: 500,
      body: JSON.stringify({ success: false, error: err.message }),
    };
  }
};

Choose Deploy (or Ctrl + Shift + U) to save your changes.

Step 3: Configure environment variables

  1. In the Configuration tab, choose Environment variables.

alt text

  1. Add the following:
S3_BUCKET=YOUR_S3_BUCKET_NAME
REKOGNITION_COLLECTION=YOUR_REKOGNITION_COLLECTION_NAME
DYNAMO_TABLE=YOUR_DYNAMO_TABLE_NAME

alt text

  1. Save changes.

Step 4: Assign IAM permissions

Your Lambda function needs permission to query data from your DynamoDB attendance table.

  1. In the Configuration tab, go to Permissions and click the role name attached to your Lambda function.

alt text

  1. In IAM, choose Add permissions → Create inline policy.

alt text

  1. Switch to JSON view and paste:
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": "dynamodb:Query",
      "Resource": "arn:aws:dynamodb:us-east-1:938108731074:table/${env:DYNAMO_TABLE}"
    }
  ]
}

Replace ${env:DYNAMO_TABLE} with your actual DynamoDB table name if environment substitution is not supported in the IAM policy editor.

  1. Save the policy and attach it to your Lambda execution role.

At this point, attendanceFunction is ready to query attendance records stored in your DynamoDB table.