kafka-observable is the easiest way to exchange messages through kafka with node.js.
Using the solid no-kafka as default client, kafka-observable creates RxJS observables that can be manipulated as if you were using Kafka Streams, but with a familiar interface to javascript developers.
Think of observables as collections which elements arrive over time. You may iterate over them, which means you can also apply filter, map or reduce.
Many of the operations provided by observables are very similar to the capabilities available in Kafka Streams, including the ability to use window (accumulate values for a period).
npm install --save kafka-observableImagine your customers can subscribe to out-of-stock products in your online store to receive emails when the product is in stock. Your stock management publishes updates to a kafka topic called inventory_updates and you mailer consumes from notifications.
const opts = {
brokers: 'kafka://kafka-broker.example.com:9092',
groupId: 'inventory-notifications'
};
const KafkaObservable = require('kafka-observable')(opts);
// assumes getWatchers will execute a network request and returns an observable
const getWatchers = require('./lib/observables/watchers');
const subscription = KafkaObservable.fromTopic('inventory_updates')
// gets messge as JSON
.let(KafkaObservable.JSONMessage())
// just arrived
.filter(({inventory}) => inventory.previous === 0 && inventory.current > 0)
// gets watchers, format message and concat 2 dimensional observable
.concatMap(product =>
getWatchers(product.id)
.map(watchers => ({ watchers, product }))
// sends formated message to new topic and concats 2 dimensional observable
.concatMap(message => KafkaObservable.toTopic('notifications', message));
subscription.subscribe(success => console.log(success), err => console.error(err)); Creates an observable that will consume from a Kafka topic.
- topic (String) - topic name
- options (Object) - client options
- adapterFactory (Object) - client adapter (Defaults to no-kafka adapter)
KafkaObservable as a function:
const opts = { brokers: 'kafka://127.0.0.1:9092', groupId: 'test' };
const KafkaObservable = require('kafka-observable')(opts);
const consumer = KafkaObservable.fromTopic('my_topic')
.map(({message}) => message.value.toString('utf8'));
consumer.subscribe(message => console.info(message));Passing options parameter to fromTopic:
const opts = { brokers: 'kafka://127.0.0.1:9092', groupId: 'test' };
const KafkaObservable = require('kafka-observable');
const consumer = KafkaObservable.fromTopic('my_topic', opts)
.map(({message}) => message.value.toString('utf8'));
consumer.subscribe(message => console.info(message));Below are the main options for the consumer. For more consumer options, please refer to no-kafka options (in case you use the provided default adapter).
| Option | Required | Type | Default | Description |
|---|---|---|---|---|
| brokers | yes | Array/String | - | list of Kafka brokers |
| groupId | yes | String | - | consumer group id |
| autoCommit | no | boolean | true | commits the message offset automatically if no exception is thrown |
| strategy | no | String | Default | name of the assignment strategy for the consumer (Default/Consistent/WeightedRoundRobin) |
Creates an observable that publishes messages to a Kafka topic.
- topic (String) - topic name
- messages (String|Array|Observable) - messages to be published in kafka topic
- options (Object) - client options
- adapterFactory (Object) - client adapter (Defaults to no-kafka adapter)
KafkaObservable as a function:
const opts = { brokers: 'kafka://127.0.0.1:9092' };
const messages = [{key: 'value1'}, {key: 'value2'}];
const KafkaObservable = require('kafka-observable')(opts);
const producer = KafkaObservable.toTopic('my_topic', messages);
producer.subscribe(message => console.info(message));Passing options parameter to toTopic:
const opts = { brokers: 'kafka://127.0.0.1:9092' };
const messages = Observable.from([{key: 'value1'}, {key: 'value2'}]);
const KafkaObservable = require('kafka-observable');
const producer = KafkaObservable.toTopic('my_topic', messages, opts);
producer.subscribe(message => console.info(message));Below are the main options for the producer. For more producer options, please refer to no-kafka options (in case you use the provided default adapter).
| Option | Required | Type | Default | Description |
|---|---|---|---|---|
| brokers | yes | Array/String | - | list of Kafka brokers |
| partitioner | no | prototype/String | Default | name (Default/HashCRC32) or prototype (instance of Kafka.DefaultPartitioner) to use as producer partitioner |
Convenience operator which converts a Buffer message value into utf8 string.
- mapper (Function) - mapper function
const opts = { brokers: 'kafka://127.0.0.1:9092', groupId: 'test' };
const KafkaObservable = require('kafka-observable');
const consumer = KafkaObservable.fromTopic('my_topic', opts)
.let(KafkaObservable.TextMessage());
consumer.subscribe(message => console.info(message));Convenience operator provided to deserialize an object from a JSON message.
- mapper (Function) - mapper function
const opts = { brokers: 'kafka://127.0.0.1:9092', groupId: 'test' };
const KafkaObservable = require('kafka-observable');
const consumer = KafkaObservable.fromTopic('my_topic', opts)
.let(KafkaObservable.JSONMessage());
consumer.subscribe(json => console.info(json.key));If you don't want to use no-kafka you can write an adapter for your client which respects
the interface established by the code in lib/client.
I currently use an internal kafka client at Netflix with an interface very similar to this adapter and I wanted it to work out-of-the-box.
npm install
npm run unit-testrequires docker to be installed and accessible through the docker command
npm install
docker pull spotify/kafka
npm run unit-testbased on unit tests
npm install
npm run coverage
open coverage/lcov-report/index.html npm install
npm run gen-docs
open out/index.html