AWS Lambda で WebP変換

index.js

'use strict';

// 全体の設定
var DST_BUCKET = 'xxxxxxxxxxx';                                // WebP が格納されるバケット
var SRC_BUCKET = 'xxxxxxxxxxx';                                // イベントソース
var ACCESS_KEY = 'XXXXXXXXXXXXXXXXXXXX';                       // アクセスキーID
var SECRET_KEY = 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX';   // シークレットキー
var REGION = 'ap-northeast-1';                                 // リージョン
var ACCEPTED_EXTENTIONS = ["png", "jpg", "gif"];               // 拡張子

// WebP に関する設定
var WEBP_QUALITY = 30;
var WEBP_PRESET = 'text';

// for node-webp
process.env.PATH = process.env.LAMBDA_TASK_ROOT;
process.env.LD_LIBRARY_PATH = process.env.LAMBDA_TASK_ROOT;

var AWS = require('aws-sdk');
var CWebp = require('cwebp').CWebp;
var path = require('path');

AWS.config.region = REGION;
AWS.config.update({ accessKeyId: ACCESS_KEY, secretAccessKey: SECRET_KEY });
var s3 = new AWS.S3();

exports.handler = function (event, context) {

    var params = {
        Bucket: event.Records[0].s3.bucket.name,
        Key: event.Records[0].s3.object.key
    };

    if (params.Bucket !== SRC_BUCKET) {
        context.done(null, 'Invalid bucket: ' + params.Bucket);
    }

    var accepted_extentions = ACCEPTED_EXTENTIONS.map(function (v) {
        return '.' + v + '$';
    });

    if (!params.Key.match(new RegExp(accepted_extentions.join('|')))) {
        context.done(null, 'It seems no image file: ' + params.Key);
    }

    console.log('Received event:', JSON.stringify(event, null, 2));
    console.log('Received context:', JSON.stringify(context, null, 2));

    s3.getObject(params, function (error, data) {
        if (error) {
            context.fail('Error getting ' + params.Key + ' from ' + params.Bucket);
            context.done();
        }
        var webp = new CWebp(data.Body);
        webp.quality(WEBP_QUALITY);
        webp.preset(WEBP_PRESET);

        webp.toBuffer().then(function (buffer) {
            s3.putObject({
                Bucket: DST_BUCKET,
                Key: params.Key.replace(path.extname(params.Key), '.webp'),
                Body: buffer
            }, function (error, data) {
                if (error) {
                    console.log('error: ' + error + ' stack: ' + error.stack);
                    context.fail('error: ' + error + ' stack: ' + error.stack);
                } else {
                    console.log('data: ' + data);
                    context.succeed('data: ' + data);
                }
            });
        })['catch'](function (e) {
            context.fail('Error converting ' + params.Key + ' to WebP from ' + params.Bucket + '. ' + e);
        });
    });
};

I am getting error with this. Any idea on this?

{
"errorMessage": "Cannot find module '/var/task/index'",
"errorType": "Error",
"stackTrace": [
"Function.Module._load (module.js:417:25)",
"Module.require (module.js:497:17)",
"require (internal/module.js:20:19)"
]
}