no-kafka

no-kafka

no-kafka is Apache Kafka 0.9 client for Node.js with new unified consumer API support. No Zookeeper connection required. Doesn't support compression yet.

All methods will return a promise

Using

• download and install Kafka
• create your test topic:

kafka-topics.sh --zookeeper 127.0.0.1:2181 --create --topic kafka-test-topic --partitions 3 --replication-factor 1

Producer

Example:

var Kafka = require('no-kafka');
var producer = new Kafka.Producer();

return producer.init().then(function(){
  return producer.send({
      topic: 'kafka-test-topic',
      partition: 0,
      message: {
          value: 'Hello!'
      }
  });
})
.then(function (result) {
  /*
  [ { topic: 'kafka-test-topic', partition: 0, offset: 353 } ]
  */
});

Producer options:

• requiredAcks - require acknoledgments for produce request. If it is 0 the server will not send any response. If it is 1 (default), the server will wait the data is written to the local log before sending a response. If it is -1 the server will block until the message is committed by all in sync replicas before sending a response. For any number > 1 the server will block waiting for this number of acknowledgements to occur (but the server will never wait for more acknowledgements than there are in-sync replicas).
• timeout - timeout in ms for produce request
• clientId - ID of this client, defaults to 'no-kafka-client'
• connectionString - comma delimited list of initial brokers list, defaults to '127.0.0.1:9092'

Simple Consumer

Manually specify topic, partition and offset when subscribing. Suitable for simple use cases.

Example:

var consumer = new Kafka.SimpleConsumer();

consumer.on('data', function (messageSet, topic, partition) {
    messageSet.forEach(function (m) {
        console.log(topic, partition, m.offset, m.message.value.toString('utf8'));
    });
});

return consumer.init().then(function () {
    return Promise.all([
        consumer.subscribe('kafka-test-topic', 0),
        consumer.subscribe('kafka-test-topic', 1)
    ]);
});

Subscribe (or change subscription) to specific offset and limit maximum received MessageSet size:

consumer.subscribe('kafka-test-topic', 0, {offset: 20, maxBytes: 30}

Subscribe to latest or earliest offsets in the topic/parition:

consumer.subscribe('kafka-test-topic', 0, {time: Kafka.LATEST_OFFSET}
consumer.subscribe('kafka-test-topic', 0, {time: Kafka.EARLIEST_OFFSET}

Commit offset(s) (V0, Kafka saves these commits to Zookeeper)

consumer.commitOffset([
  {
      topic: 'kafka-test-topic',
      partition: 0,
      offset: 1
  },
  {
      topic: 'kafka-test-topic',
      partition: 1,
      offset: 2
  }
])

Fetch commited offset(s)

consumer.fetchOffset([
  {
      topic: 'kafka-test-topic',
      partition: 0
  },
  {
      topic: 'kafka-test-topic',
      partition: 1
  }
]).then(function (result) {
/*
[ { topicName: 'kafka-test-topic',
    partitions:
     [ { partition: 0,
         offset: 1,
         metadata: null,
         error: null },
       { partition: 1,
         offset: 2,
         metadata: null,
         error: null },
      ] 
    },
]
*/
});

Simple Consumer options

• groupId - group ID for comitting and fetching offsets. Defaults to 'no-kafka-group-v0'
• timeout - timeout for fetch requests, defaults to 100ms
• idleTimeout - timeout between fetch calls, defaults to 1000ms
• minBytes - minimum number of bytes to wait from Kafka before returning the fetch call, defaults to 1 byte
• maxBytes - maximum size of messages in a fetch response
• clientId - ID of this client, defaults to 'no-kafka-client'
• connectionString - comma delimited list of initial brokers list, defaults to '127.0.0.1:9092'

Group Consumer (new unified consumer API)

Specify an assignment strategy (or use no-kafka built-in consistent assignment strategy) and subscribe by specifying only topics. Elected group leader will automatically assign partitions between all group members.

Example:

var consumer = new Kafka.GroupConsumer();
var strategies = [{
    strategy: 'TestStrategy',
    subscriptions: ['kafka-test-topic'],
    metadata: {
        id: process.argv[2] || 'consumer_1',
        weight: 50
    }
}];

consumer.on('data', function (messageSet, topic, partition) {
    messageSet.forEach(function (m) {
        console.log(topic, partition, m.offset, m.message.value.toString('utf8'));
        // process each message and commit its offset
        consumer.commitOffset({topic: topic, partition: partition, offset: m.offset, metadata: 'optional'});
    });
});

return consumer.init(strategies).then(function(){
  // all done, now wait for messages in event listener
});

Assignment strategies

no-kafka provides two built-in strategies:

• GroupConsumer.ConsistentAssignment which is based on a consisten hash ring and so provides consistent assignment across consumers in a group based on supplied metadata.id and metadata.weight options.
• GroupConsumer.RoundRobinAssignment simple range assignment.

Using GroupConsumer.ConsistentAssignment (default in no-kafka):

var strategies = {
    strategy: 'TestStrategy',
    subscriptions: ['kafka-test-topic'],
    metadata: {
        id: process.argv[2] || 'consumer_1',
        weight: 50
    }
};
// consumer.init(strategy)....

Note that each consumer in a group should have its own and consistent metadata.id.

Using GroupConsumer.RoundRobinAssignment:

var strategies = {
    strategy: 'TestStrategy',
    subscriptions: ['kafka-test-topic'],
    fn: Kafka.GroupConsumer.RoundRobinAssignment
};
// consumer.init(strategy)....

You can also write your own assignment strategy function and provide it as fn options of the strategy item.