Find AWS lambda cold start durations

README.md

Full code I used to get the amount and duration of AWS Lambda cold starts during 2 given months.

Also see the question on StackOverflow.

index.ts

import AWS from "aws-sdk";
import fs from "fs";
import util from "util";

const appendFilePromise = util.promisify(fs.appendFile);

const logGroupName = `/aws/lambda/...`;
const cloudWatchLogs = new AWS.CloudWatchLogs({ region: "eu-west-1" });

async function main(month: string) {
    let next = true;
    let nextToken = "";

    while (next) {
        let params: any = {
            logGroupName,
            logStreamNamePrefix: `2019/${month}`,
            descending: true
        };

        if (nextToken !== "") {
            params.nextToken = nextToken;
        }

        try {
            const response = await cloudWatchLogs.describeLogStreams(params).promise();

            const logStreams = response.logStreams;

            for (let logStream of logStreams) {
                try {
                    const events = await cloudWatchLogs.getLogEvents({
                        logGroupName,
                        logStreamName: logStream.logStreamName,
                        startFromHead: true
                    }).promise();
    
                    for (let event of events.events) {
                        if (event.message.startsWith("REPORT")) {
                            const duration = /Duration:(.*)Billed/.exec(event.message);
                            if (duration) {
                                console.log(`${logStream.logStreamName}  --  ${duration[1]}`);
                                await appendFilePromise(`2019-${month}.csv`, `${logStream.logStreamName},${duration[1]}\n`);
                            } else {
                                console.error("No duration found for : " + event.message);
                            }
    
                            break;
                        }
                    }
                } catch (e) {
                    console.error(e);
                }
            }

            if (response.nextToken) {
                nextToken = response.nextToken;
                next = true;
            } else {
                next = false;
            }
        } catch (e) {
            console.error(e);
        }
    }
}

(async () => {
    try {
        await Promise.all([main("05"), main("06")])
    } catch (e) {
        console.log(e);
    }
})();