Cloudwatch Logs to S3 exporter AWS Lambda function code

cloudwatch_logs.js

const AWS = require('aws-sdk');
const cloudwatchLogs = new AWS.CloudWatchLogs();

function getDatePath(date) {
    date = date || new Date();
    const dateString = date.toISOString().substring(0, 10);
    return dateString.replace(/-/g, '/');
}

function getLogPathForS3(logGroupName) {
    const logPathParts = logGroupName.split('/');
    const mainParts = logPathParts[0].split('-');
    let logPath = mainParts.slice(1).join('/');
    if(logPathParts.length > 1) {
        logPath = logPath + '-' + logPathParts.slice(1).join('-');
    }
    return logPath;
}

function getYesterdayDate() {
    const date = new Date();
    date.setUTCDate(date.getUTCDate() - 1);
    return date;
}

function getDayStartTimestamp(date) {
    date = date || new Date();
    date.setUTCHours(0);
    date.setUTCMinutes(0);
    date.setUTCSeconds(0);
    date.setUTCMilliseconds(0);
    return date.getTime();
}


exports.getLogGroupNames = (prefix, nextToken) => {
    return cloudwatchLogs.describeLogGroups({
        nextToken: nextToken,
        logGroupNamePrefix: prefix,
        limit: 1
    }).promise();
};


function describeExportTask(taskId) {
    return cloudwatchLogs.describeExportTasks({taskId}).promise();
}

function waitForExportTaskToComplete(taskId) {
    return new Promise((resolve, reject) => {
        describeExportTask(taskId).then((response) => {
            const task = response.exportTasks[0];
            const taskStatus = task.status.code;
            if(taskStatus === 'RUNNING' || taskStatus.indexOf('PENDING') === 0) {
                console.log("Task is still running for", task.logGroupName);
                setTimeout(() => {
                    waitForExportTaskToComplete(taskId).then(resolve).catch(reject);
                }, 1000);
            } else {
                console.log("Task is completed for", task.logGroupName, "with status", taskStatus);
                resolve();
            }
        }).catch(reject);
    }); 
}

exports.createExportTask = (logGroupName, s3Bucket, logFolderName) => {
    const yesterdayDate = getYesterdayDate();
    const logPathForS3 = getLogPathForS3(logGroupName);
    return cloudwatchLogs.createExportTask({
        destination: s3Bucket,
        destinationPrefix: `${logFolderName}/${logPathForS3}/${getDatePath(yesterdayDate)}`,
        logGroupName,
        from: getDayStartTimestamp(yesterdayDate),
        to: getDayStartTimestamp()
    }).promise().then((response) => {
        console.log("Task is started for", logGroupName);
        return waitForExportTaskToComplete(response.taskId);
    });
};

index.js

const cloudwatchLogUtils = require('./cloudwatch_logs');

exports.handler = (event, context, callback) => {
    const nextToken = event.nextToken;
    const logGroupNamePrefix = event.logGroupNamePrefix;
    cloudwatchLogUtils.getLogGroupNames(logGroupNamePrefix, nextToken)
    .then((response) => {
        event.nextToken = response.nextToken;
        event.continue = event.nextToken !== undefined;
        const logGroupName = response.logGroups[0].logGroupName;
        return cloudwatchLogUtils.createExportTask(logGroupName, event.s3Bucket, event.logFolderName);
    }).then(() => {
        console.log("Successfully created export task");
        return callback(null, event);  
    }).catch((err) => {
        console.error(err);
        callback(err);
    });
};