Atomic DynamoDB increment and creation/update time with Axios/API Gateway/Lambda

atomic-counter-lambda-handler.js

const aws = require('aws-sdk');
const dynamodb = new aws.DynamoDB.DocumentClient();

let corsHeaders = {
    'Access-Control-Allow-Origin': process.env.CORS_ORIGIN,
    'Access-Control-Allow-Credentials': true,
};

exports.handler = async () => {
    const promise = new Promise(async (resolve) => {
        try {
            let response = await dynamodb.update({
                TableName: process.env.TABLE_NAME,
                Key: { "hashKeyName": "identity" },
                UpdateExpression:
                    `set creation_time = if_not_exists(creation_time, :update_time),
                    update_time = :update_time,
                    num_updates = if_not_exists(num_updates, :zero) + :increase`,
                ExpressionAttributeValues: {
                    ":update_time": Date.now(),
                    ":increase": 1,
                    ":zero": 0
                },
                ReturnValues: "ALL_NEW"
            }).promise();
            resolve({
                "isBase64Encoded": false,
                "statusCode": 200,
                "headers": corsHeaders,
                "body": JSON.stringify(response)
            });
        } catch (err) {
            console.error(err);
            resolve({
                "isBase64Encoded": false,
                "statusCode": 500,
                "headers": corsHeaders,
                "body": JSON.stringify(err)
            });
        }
    });
    return promise;
};

test-atomic-counter.js

const axios = require('axios');
const http = require('http');
http.globalAgent.maxSockets = 150;

let min, max;
let responseValues = {};

let promises = [];
for (let i = 0; i < 500; i++) {
    promises.push(axios({
        method: 'post',
        url: 'https://a1b2c3d4e5.execute-api.us-east-1.amazonaws.com/prod/atomic-update',
        data: {},
        headers: {
            'Content-Type': 'application/json',
            'x-api-key': 'abCDefGHijKLmnOPqrSTuvWXyz' // throttling set to 2000/200
        }
    }));
}

Promise.all(promises)
.then(results => {
    results.forEach(result => {
        let counter = result?.data?.Attributes?.num_updates;
        if (counter) {
            responseValues[counter] = responseValues[counter] ? responseValues[counter] + 1 : 1;
            if (!min || counter < min) min = counter;
            if (!max || counter > max) max = counter;
        }
    });
    let unexpected = [];
    for (key in responseValues) {
        if (responseValues[key] !== 1) unexpected.push(key);
    }
    console.log(`min: ${min}, max: ${max}, unexpected: ${unexpected}`);
})
.catch(console.error);