index.js

const AWS = require('aws-sdk');
const gm = require('gm').subClass({ imageMagick: true });
const s3 = new AWS.S3();

exports.handler = (event, context, callback) => {
  const Bucket = event.Records[0].s3.bucket.name;
  const Key = event.Records[0].s3.object.key;
  const filename = Key.split('/')[Key.split('/').length - 1];
  const ext = Key.split('.')[Key.split('.').length - 1];

  s3.getObject({ Bucket, Key }, (err, data) => {
    if (err) {
      console.log(`Image load error: ${err}`);
      return callback(err);
    }
    return gm(data.Body)
      .resize(200, 200, '^')
      .quality(90)
      .toBuffer(ext, (err, buffer) => {
        if (err) {
          console.log(`Image resizing err: ${err}`);
          return callback(err);
        }
        return s3.putObject({
          Bucket,
          Key: `thumb/${filename}`,
          Body: buffer,
        }, (err) => {
          if (err) {
            console.log(`Image upload err: ${err}`);
            return callback(err);
          }
          return callback(null, `goods/${filename}`);
        })
      });
  });
};