Node.js Kinesis Aggregation & Deaggregation Modules

These Kinesis Aggregation and Deaggregation modules provide a simple interface for creating and working with data using the Kinesis Aggregated Record Format from any type of application. If you are generating Kinesis records using the Kinesis Producer Library (KPL), you can easily deaggregate and process that data from node.js. Alternatively, if you want to create Kinesis records that are tightly packed to reach the maximum record size, then this is straightforward to achieve. Using record aggregation improves throughput and reduces costs when writing applications that publish data to and consume data from Amazon Kinesis.

Installation

The Node.js record aggregation/deaggregation modules are available on NPM as aws-kinesis-agg. To get started, include the aws-kinesis-agg module from npm into your new or existing NodeJS application:

``
var agg = require('aws-kinesis-agg');
`

Record Deaggregation

When using deaggregation, you provide a single aggregated Kinesis Record and get back multiple Kinesis User Records. If a Kinesis record that is provided is not using the Kinesis Aggregated Record Format, that's perfectly fine - you'll just get a single record output from the single record input. A Kinesis User Record that is returned from the deaggregation module looks like:

`
{
partitionKey : String - The Partition Key provided when the record was submitted
explicitPartitionKey : String - The Partition Key provided for the purposes of Shard Allocation
sequenceNumber : BigInt - The sequence number assigned to the record on submission to Kinesis
subSequenceNumber : Int - The sub-sequence number for the User Record in the aggregated record, if aggregation was in use by the producer
data : Buffer - The original data transmitted by the producer (base64 encoded)
}
`

When you receive a Kinesis Record in your consumer application, you will extract the User Records using deaggregation methods in the aws-kinesis-agg module. The aws-kinesis-agg module provides both syncronous and asyncronous methods of deaggregating records.

$3

The syncronous model of deaggregation extracts all the Kinesis User Records from the received Kinesis Record, and accumulates them into an array. The method then makes a callback with any errors encountered, and the array of User Records that were deaggregated:

`
deaggregateSync(kinesisRecord, computeChecksums, afterRecordCallback(err, UserRecord[]);
`

$3

The asyncronous model of deaggregation allows you to provide a callback which is invoked for each User Record that is extracted from the Kinesis Record. When all User Records have been extracted from the Kinesis Record, an `afterRecordCallback` is invoked which allows you to continue processing additional Kinesis Records that your consumer receives:

`
deaggregate(kinesisRecord, computeChecksums, perRecordCallback(err, UserRecord), afterRecordCallback(err, errorKinesisRecord));
`
If any errors are encountered during processing of the perRecordCallback, then the afterRecordCallback is called with the err plus an error Record which contains the failed subSequenceNumber from the aggregated data with details about the enclosing Kinesis Record:

`
{
partitionKey : String - The Partition Key of the enclosing Kinesis Aggregated Record
explicitPartitionKey : String - The Partition Key provided for the purposes of Shard Allocation
sequenceNumber : BigInt - The sequence number assigned to the record on submission of the Aggregated Record by the encoder
subSequenceNumber : Int - The sub-sequence number for the failing User Record in the aggregated record, if aggregation was in use by the producer
data : Buffer - The original protobuf message transmitted by the producer (base64 encoded)
}
`

The computeChecksums parameter accepts a Boolean that indicates whether the checksum in the kinesis record should be validated. If the checksum is incorrect, an error will be returned via the afterRecordCallback.

Record Aggregation

Applications implemented in AWS Lambda often emit new events based on the events that were received in the function. They may be doing enrichment, parsing, or filtering, and the ability to take advantage of Kinesis record-based aggregation will result in more efficient systems.

$3

To use Aggregation, you simply use aggregate function.

`
aggregate(records, encodedRecordHandler, afterPutAggregatedRecords, errorCallback)

`

With:
- encodedRecordHandler: a callback function (record, (err, data) => ...) invoked when the number of records supplied exceeds the Kinesis maximum record size (1MB as of March 2016). record has field {data, partitionKey, explicitHashKey}
- afterPutAggregatedRecords: a callback invoked when all call of encodedRecordHandler are finished.
- errorCallback: a function (err, data) called each time that an error occurs


The following example demonstrates an AWS Lambda function that was does per-record processing and then transmits those record to Amazon Kinesis (pseudo code):

`
// create a record aggregator
const aggregate = require('aws-kinesis-agg').aggregate;

// create the function which sends data to Kinesis with a random partition key
var onReady = function(encodedRecord, callback) {
// build putRecords params
const params = {
Data: encodedRecord.data,
PartitionKey: encodedRecord.partitionKey,
StreamName: 'my-stream'
}
if (encodedRecord.explicitHashKey) {
params.ExplicitHashKey = encodedRecord.explicitHashKey
}
// send to kinesis
// kinesisClient.putRecord(param , ...)
myKinesisConnection.putRecord(params, callback)
};

aggregator.aggregate(event.Records, onReady, () => {
// lambda is done close context
...
}, (err, data) => {
console.log(${err}, ${data})
})

`

Examples

This module includes an example AWS Lambda function in the example` folder, which gives you easy ability to build new functions to process Kinesis aggregated message data. Both examples use async.js to process the received Kinesis Records.

----

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