Kinesis Firehose Data Transformation Lambda

index.js

const redact = function (str) {
    return str[0] + "*".repeat(str.length - 2) + str.slice(-1);
}

const transform = (data) => {
    // decode Kinesis Data Firehose raw data and convert it to JSON object
    var parsedData = JSON.parse(new Buffer.from(data,'base64').toString('utf8'));

    // you can now transform the JSON object

    // 1. extract properties to top level
    parsedData.status = parsedData.detail.status;
    // 2. redact fields
    parsedData.email = redact(parsedData.email)
    // 3. or even delete fields
    delete parsedData.detail;

    // convert back to base64 encoded string
    return new Buffer.from(JSON.stringify(parsedData) + '\n').toString('base64');
}

exports.handler = async (event, context) => {
    const output = event.records.map((record) => ({
        recordId: record.recordId,
        result: 'Ok',
        data: transform(record.data),
    }));
    return { records: output };
};