Producing Messages

To publish messages to Kafka you have to create a producer. Simply call the producer function of the client to create it:

const producer = kafka.producer()

or with options

const producer = kafka.producer({
    allowAutoTopicCreation: false,
    transactionTimeout: 30000
})

Options

option	description	default
createPartitioner	Take a look at Custom Partitioner for more information	`null`
retry	Take a look at Producer Retry for more information	`null`
metadataMaxAge	The period of time in milliseconds after which we force a refresh of metadata even if we haven't seen any partition leadership changes to proactively discover any new brokers or partitions	`300000` - 5 minutes
allowAutoTopicCreation	Allow topic creation when querying metadata for non-existent topics	`true`
transactionTimeout	The maximum amount of time in ms that the transaction coordinator will wait for a transaction status update from the producer before proactively aborting the ongoing transaction. If this value is larger than the `transaction.max.timeout.ms` setting in the broker, the request will fail with a `InvalidTransactionTimeout` error	`60000`
idempotent	Experimental. If enabled producer will ensure each message is written exactly once. Acks must be set to -1 ("all"). Retries will default to MAX_SAFE_INTEGER.	`false`
maxInFlightRequests	Max number of requests that may be in progress at any time. If falsey then no limit.	`null` (no limit)

Producing messages

The method send is used to publish messages to the Kafka cluster.

const producer = kafka.producer()

await producer.connect()
await producer.send({
    topic: 'topic-name',
    messages: [
        { key: 'key1', value: 'hello world' },
        { key: 'key2', value: 'hey hey!' }
    ],
})

Example with a defined partition:

const producer = kafka.producer()

await producer.connect()
await producer.send({
    topic: 'topic-name',
    messages: [
        { key: 'key1', value: 'hello world', partition: 0 },
        { key: 'key2', value: 'hey hey!', partition: 1 }
    ],
})

The method send has the following signature:

await producer.send({
    topic: <String>,
    messages: <Message[]>,
    acks: <Number>,
    timeout: <Number>,
    compression: <CompressionTypes>,
})

property	description	default
topic	topic name
messages	An array of objects. See Message structure for more details. Example: `[{ key: 'my-key', value: 'my-value'}]`
acks	Control the number of required acks. -1 = all insync replicas must acknowledge (default) 0 = no acknowledgments 1 = only waits for the leader to acknowledge	`-1` all insync replicas must acknowledge
timeout	The time to await a response in ms	`30000`
compression	Compression codec	`CompressionTypes.None`

Message structure

Messages have the following properties:

Property	Description	Default
key	Used for partitioning. See Key
value	Your message content. The value can be a Buffer, a string or null. The value will always be encoded as bytes when sent to Kafka. When consumed, the consumer will need to interpret the value according to your schema.
partition	Which partition to send the message to. See Key for details on how the partition is decided if this property is omitted.
timestamp	The timestamp of when the message was created. See Timestamp for details.	`Date.now()`
headers	Metadata to associate with your message. See Headers.

Key

The message key is used to decide which partition the message will be sent to. This is important to ensure that messages relating to the same aggregate are processed in order. For example, if you use an orderId as the key, you can ensure that all messages regarding that order will be processed in order.

By default, the producer is configured to distribute the messages with the following logic:

If a partition is specified in the message, use it
If no partition is specified but a key is present choose a partition based on a hash (murmur2) of the key
If no partition or key is present choose a partition in a round-robin fashion

Timestamp

Each message has a timestamp in the form of a UTC timestamp with millisecond precision as a string. If no timestamp was provided, the producer will use the current time as the timestamp. When the message is consumed, the broker may override this timestamp depending on the topic configuration:

If the topic is configured to use CreateTime, the timestamp from the producer's message will be used.
If the topic is configured to use LogAppendTime, the timestamp will be overwritten by the broker with the broker local time when it appends the message to its log.

Headers

Kafka v0.11 introduces record headers, which allows your messages to carry extra metadata. To send headers with your message, include the key headers with the values. Example:

await producer.send({
    topic: 'topic-name',
    messages: [{
        key: 'key1',
        value: 'hello world',
        headers: {
            'correlation-id': '2bfb68bb-893a-423b-a7fa-7b568cad5b67',
            'system-id': 'my-system',
        }
    }]
})

A header value can be either a string or an array of strings.

Producing to multiple topics

To produce to multiple topics at the same time, use sendBatch. This can be useful, for example, when migrating between two topics.

const topicMessages = [
  {
    topic: 'topic-a',
    messages: [{ key: 'key', value: 'hello topic-a' }],
  },
  {
    topic: 'topic-b',
    messages: [{ key: 'key', value: 'hello topic-b' }],
  },
  {
    topic: 'topic-c',
    messages: [
      {
        key: 'key',
        value: 'hello topic-c',
        headers: {
          'correlation-id': '2bfb68bb-893a-423b-a7fa-7b568cad5b67',
        },
      }
    ],
  }
]
await producer.sendBatch({ topicMessages })

sendBatch has the same signature as send, except topic and messages are replaced with topicMessages:

await producer.sendBatch({
    topicMessages: <TopicMessages[]>,
    acks: <Number>,
    timeout: <Number>,
    compression: <CompressionTypes>,
})

property	description
topicMessages	An array of objects with `topic` and `messages`. `messages` is an array of the same type as for `send`.

Custom partitioner

It's possible to assign a custom partitioner to the producer. A partitioner is a function which returns another function responsible for the partition selection, something like this:

const MyPartitioner = () => {
    return ({ topic, partitionMetadata, message }) => {
        // select a partition based on some logic
        // return the partition number
        return 0
    }
}

partitionMetadata is an array of partitions with the following structure:

{ partitionId: <NodeId>, leader: <NodeId> }

Example:

[
    { partitionId: 1, leader: 1 },
    { partitionId: 2, leader: 2 },
    { partitionId: 0, leader: 0 }
]

To use your custom partitioner, use the option createPartitioner when creating the producer.

kafka.producer({ createPartitioner: MyPartitioner })

Default Partitioners

KafkaJS ships with 2 partitioners: DefaultPartitioner and LegacyPartitioner.

The DefaultPartitioner should be compatible with the default partitioner that ships with the Java Kafka client. This can be important to meet the co-partitioning requirement when joining multiple topics.

🚨 Important 🚨

The LegacyPartitioner was the default until v2.0.0. If you are upgrading from a version older and want to retain the previous partitioning behavior, use the LegacyPartitioner by importing it and providing it to the Producer constructor:
const { Partitioners } = require('kafkajs')
kafka.producer({ createPartitioner: Partitioners.LegacyPartitioner })

Retry

The option retry can be used to customize the configuration for the producer.

Take a look at Retry for more information.

Compression

Since KafkaJS aims to have as small footprint and as few dependencies as possible, only the GZIP codec is part of the core functionality, other codecs are available as packages.

GZIP

const { CompressionTypes } = require('kafkajs')

async () => {
  await producer.send({
    topic: 'topic-name',
    compression: CompressionTypes.GZIP,
    messages: [
        { key: 'key1', value: 'hello world' },
        { key: 'key2', value: 'hey hey!' }
    ],
  })
}

The consumers know how to decompress GZIP, so no further work is necessary.

Snappy

Snappy support is provided by the package kafkajs-snappy

npm install --save kafkajs-snappy
# yarn add kafkajs-snappy

const {  CompressionTypes, CompressionCodecs } = require('kafkajs')
const SnappyCodec = require('kafkajs-snappy')

CompressionCodecs[CompressionTypes.Snappy] = SnappyCodec

Take a look at the official readme for more information

LZ4

LZ4 support is provided by the package kafkajs-lz4

npm install --save kafkajs-lz4
# yarn add kafkajs-lz4

const { CompressionTypes, CompressionCodecs } = require('kafkajs')
const LZ4 = require('kafkajs-lz4')

CompressionCodecs[CompressionTypes.LZ4] = new LZ4().codec

The package also accepts options to granularly control LZ4 compression & decompression. Take a look at the official readme for more information.

ZSTD

Zstandard support is provided by @kafkajs/zstd

npm install --save @kafkajs/zstd
# yarn add @kafkajs/zstd

const { CompressionTypes, CompressionCodecs } = require('kafkajs')
const ZstdCodec = require('@kafkajs/zstd')

CompressionCodecs[CompressionTypes.ZSTD] = ZstdCodec()

Configuration options can be passed to the factory function to control compression & decompression levels and other features. See the official readme for more information.

Other

Any other codec can be easily implemented using existing libraries.

A codec is an object with two async functions: compress and decompress. Import the libraries and define the codec object:

const MyCustomSnappyCodec = {
    async compress(encoder) {
        return someCompressFunction(encoder.buffer)
    },

    async decompress(buffer) {
        return someDecompressFunction(buffer)
    }
}

Now that we have the codec object, we can wrap it in a function and add it to the implementation:

const { CompressionTypes, CompressionCodecs } = require('kafkajs')
CompressionCodecs[CompressionTypes.Snappy] = () => MyCustomSnappyCodec

The new codec can now be used with the send method, example:

await producer.send({
    topic: 'topic-name',
    compression: CompressionTypes.Snappy,
    messages: [
        { key: 'key1', value: 'hello world' },
        { key: 'key2', value: 'hey hey!' }
    ],
})