1.js

// async waterfall (see: https://github.com/caolan/async)
async.waterfall(
    [
        // upload file to amazon s3
        function(cb) {
            // initialize knox client
            var knoxClient = knox.createClient({
                key: config.s3.key,
                secret: config.s3.secret,
                bucket: config.s3.bucket,
            });
            // send put via knox
            knoxClient.putFile(
                file.image.path,
                'uploads/' + data.filename,
                {
                    'Content-Type': file.image.type,
                    'x-amz-acl': 'public-read',
                },
                function(err, result) {
                    if (err || result.statusCode != 200) {
                        cb(err);
                    } else {
                        cb(null);
                    }
                },
            );
        },
...