fastify-kafkajs is a Fastify plugin which adds support for KafkaJS - a modern Apache Kafka client written in pure JavaScript, without librdkafka bindings.

• Decorates the Fastify instance with kafka object exposing a client (KafkaJS client instance), producer (a single, pre-connected KafkaJS producer) and consumers (array of consumers declared in plugin options).
• Disconnects the producer and consumers when the Fastify onClose hook is triggered.
• Has 100% test coverage.

npm install fastify-kafkajs

const app = fastify();

app.register(fastifyKafkaJS, {
    clientConfig: {
        brokers: ['localhost:9092'],
        clientId: 'demo-app'
    },
    consumers: [
        {
            consumerConfig: {
                groupId: 'example-consumer-group'
            },
            subscription: {
                topics: ['test-topic'],
                fromBeginning: false
            },
            runConfig: {
                eachMessage: async ({ message }) => {
                    console.log(`Consumed message: ${message.value}`);
                }
            }
        }
    ]
});

app.post('/produce', async (request, reply) => {
    return app.kafka.producer.send({
        topic: 'test-topic',
        messages: [{ key: 'key1', value: randomUUID() }]
    });
});

A complete example is available in the example folder.

By default, fastify-kafkajs disconnects the producer and consumers when the application's onClose hook is triggered. You can opt-out of this default behavior by setting the ignoreOnClose option to false.

In order to ensure that the onClose hook is triggered when the process receives SIGINT or SIGTERM (thus allowing fastify-kafkajs to disconnect the producer and consumers and preventing delayed consumer group re-balancing), usage of fastify-graceful-shutdown plugin is recommended.

npm install fastify-graceful-shutdown

import fastifyGracefulShutdown from 'fastify-graceful-shutdown';

fastify.register(fastifyGracefulShutdown);

The config object passed as a second parameter passed to register() is optional (since 3 out of 4 keys have default values, and a KafkaJS producer can be initialized with default values when provided with empty config) and has the following schema:

interface FastifyKafkaJSOptions {
    /**
     * KafkaJS client config
     * @default {
     *   brokers: ['localhost:9092'],
     *   clientId: 'fastify-kafkajs'
     * }
     */
    clientConfig?: KafkaConfig;
    /**
     * KafkaJS producer config
     */
    producerConfig?: ProducerConfig;
    /**
     * Array of objects describing consumers
     * @default []
     */
    consumers?: FastifyKafkaJSConsumerDeclaration[];
    /**
     * Ignore the default onClose handled which closes the producer
     * and all consumers. If set to true, you will have to manage
     * closing the producer and the consumers yourself.
     * @default false
     */
    ignoreOnClose?: boolean;
}

where FastifyKafkaJSConsumerDeclaration has the following keys:

• consumerConfig - Consumer config passed to KafkaJS.consumer() during consumer creation
• subscription - parameter passed to Consumer.subscribe()
• runConfig - config object passed to Consumer.run()

Upon being registered, fastify-kafkajs decorates the FastifyInstance with kafka exposing the following keys:

• client - a KafkaJS client instance
• producer - a single, pre-connected KafkaJS producer (initialized with config specified in clientConfig options key)
• consumers - array of pre-connected, subscribed and started KafkaJS consumers, declared in subscribers options key