@heroku/no-kafka/README.md

Apache Kafka 0.9 client for Node.JS

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# no-kafka

__no-kafka__ is [Apache Kafka](https://kafka.apache.org) 0.9 client for Node.js with [new unified consumer API](#groupconsumer-new-unified-consumer-api) support.

Supports sync and async Gzip and Snappy compression, producer batching and controllable retries, offers few predefined group assignment strategies and producer partitioner option.

All methods will return a [promise](https://github.com/petkaantonov/bluebird)

* [Using](#using)
* [Producer](#producer)
  * [Keyed Messages](#keyed-messages)
  * [Batching (grouping) produce requests](#batching-grouping-produce-requests)
  * [Producer options](#producer-options)
* [Simple Consumer](#simpleconsumer)
  * [Simple Consumer options](#simpleconsumer-options)
* [Group Consumer](#groupconsumer-new-unified-consumer-api)
  * [Assignment strategies](#assignment-strategies)
  * [Group Consumer options](#groupconsumer-options)
* [Group Admin](#groupadmin-consumer-groups-api)
* [Compression](#compression)
* [Connection](#connection)
* [Logging](#logging)
* [Topic Creation](#topic-creation)
* [License](#license)

## Using

* [download and install Kafka](https://kafka.apache.org/documentation.html#quickstart)
* create your test topic:

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

* install __no-kafka__

```shell
npm install no-kafka
```


## Producer

Example:

```javascript
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 } ]
  */
});
```

Send and retry if failed 2 times with 100ms delay:

```javascript
return producer.send(messages, {
  retries: {
    attempts: 2,
    delay: 100
  }
});
```

### Batching (grouping) produce requests

Accumulate messages into single batch until their total size is >= 1024 bytes or 100ms timeout expires (overwrite Producer constructor options):

```javascript
producer.send(messages, {
  batch: {
    size: 1024,
    maxWait: 100
  }
});
producer.send(messages, {
  batch: {
    size: 1024,
    maxWait: 100
  }
});
```

Please note, that if you pass different options to the `send()` method then these messages will be grouped into separate batches:

```javascript
// will be sent in batch 1
producer.send(messages, {
  batch: {
    size: 1024,
    maxWait: 100
  },
  codec: Kafka.COMPRESSION_GZIP
});
// will be sent in batch 2
producer.send(messages, {
  batch: {
    size: 1024,
    maxWait: 100
  },
  codec: Kafka.COMPRESSION_SNAPPY
});
```

### Keyed Messages

Send a message with the key:

```javascript
producer.send({
    topic: 'kafka-test-topic',
    partition: 0,
    message: {
        key: 'some-key'
        value: 'Hello!'
    }
});
```

### 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'
* `partitioner` - function used to determine topic partition for message. If message already specifies a partition, the partitioner won't be used. The partitioner function receives 3 arguments: the topic name, an array with topic partitions, and the message (useful to partition by key, etc.). `partitioner` can be sync or async (return a Promise).
* `retries` - controls number of attempts at delay between them when produce request fails
  * `attempts` - number of total attempts to send the message, defaults to 3
  * `delay` - delay in ms between retries, defaults to 1000
* `codec` - compression codec, one of Kafka.COMPRESSION_NONE, Kafka.COMPRESSION_SNAPPY, Kafka.COMPRESSION_GZIP
* `batch` - control batching (grouping) of requests
  * `size` - group messages together into single batch until their total size exceeds this value, defaults to 16384 bytes. Set to 0 to disable batching.
  * `maxWait` - send grouped messages after this amount of milliseconds expire even if their total size doesn't exceed `batch.size` yet, defaults to 10ms. Set to 0 to disable batching.
* `asyncCompression` - boolean, use asynchronouse compression instead of synchronous, defaults to `false`

## SimpleConsumer

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

Example:

```javascript
var consumer = new Kafka.SimpleConsumer();

// data handler function can return a Promise
var dataHandler = function (messageSet, topic, partition) {
    messageSet.forEach(function (m) {
        console.log(topic, partition, m.offset, m.message.value.toString('utf8'));
    });
};

return consumer.init().then(function () {
    // Subscribe partitons 0 and 1 in a topic:
    return consumer.subscribe('kafka-test-topic', [0, 1], dataHandler);
});
```

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

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

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

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

Subscribe to all partitions in a topic:

```javascript
consumer.subscribe('kafka-test-topic', dataHandler)
```

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

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

Fetch commited offset(s)

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

### SimpleConsumer options
* `groupId` - group ID for comitting and fetching offsets. Defaults to 'no-kafka-group-v0'
* `maxWaitTime` - maximum amount of time in milliseconds to block waiting if insufficient data is available at the time the fetch request is issued, 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'
* `recoveryOffset` - recovery position (time) which will used to recover subscription in case of OffsetOutOfRange error, defaults to Kafka.LATEST_OFFSET
* `asyncCompression` - boolean, use asynchronouse decompression instead of synchronous, defaults to `false`
* `handlerConcurrency` - specify concurrency level for the consumer handler function, defaults to 10

## GroupConsumer (new unified consumer API)

Specify an assignment strategy (or use __no-kafka__ built-in consistent or round robin assignment strategy) and subscribe by specifying only topics. Elected group leader will automatically assign partitions between all group members.

Example:

```javascript
var Promise = require('bluebird');
var consumer = new Kafka.GroupConsumer();

var dataHandler = function (messageSet, topic, partition) {
    return Promise.each(messageSet, function (m){
        console.log(topic, partition, m.offset, m.message.value.toString('utf8'));
        // commit offset
        return consumer.commitOffset({topic: topic, partition: partition, offset: m.offset, metadata: 'optional'});
    });
};

var strategies = [{
    strategy: 'TestStrategy',
    subscriptions: ['kafka-test-topic'],
    handler: dataHandler
}];

consumer.init(strategies); // all done, now wait for messages in dataHandler
```

### Assignment strategies

__no-kafka__ provides three built-in strategies:
* `Kafka.WeightedRoundRobinAssignment` weighted round robin assignment (based on [wrr-pool](https://github.com/oleksiyk/wrr-pool)).
* `Kafka.ConsistentAssignment` which is based on a consistent [hash ring](https://github.com/3rd-Eden/node-hashring) and so provides consistent assignment across consumers in a group based on supplied `metadata.id` and `metadata.weight` options.
* `Kafka.RoundRobinAssignment` simple assignment strategy (default).

Using `Kafka.WeightedRoundRobinAssignment`:

```javascript
var strategies = {
    strategy: 'TestStrategy',
    subscriptions: ['kafka-test-topic'],
    metadata: {
        weight: 4
    },
    fn: Kafka.WeightedRoundRobinAssignment,
    handler: dataHandler
};
// consumer.init(strategies)....
```

Using `Kafka.ConsistentAssignment`:

```javascript
var strategies = {
    strategy: 'TestStrategy',
    subscriptions: ['kafka-test-topic'],
    metadata: {
        id: process.argv[2] || 'consumer_1',
        weight: 50
    },
    fn: Kafka.ConsistentAssignment,
    handler: dataHandler
};
// consumer.init(strategies)....
```
Note that each consumer in a group should have its own and consistent metadata.id.

Using `Kafka.RoundRobinAssignment` (default in __no-kafka__):

```javascript
var strategies = {
    strategy: 'TestStrategy',
    subscriptions: ['kafka-test-topic'],
    handler: dataHandler
};
// consumer.init(strategies)....
```

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

### GroupConsumer options

* `groupId` - group ID for comitting and fetching offsets. Defaults to 'no-kafka-group-v0.9'
* `maxWaitTime` - maximum amount of time in milliseconds to block waiting if insufficient data is available at the time the fetch request is issued, 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'
* `sessionTimeout` - session timeout in ms, min 6000, max 30000, defaults to `15000`
* `heartbeatTimeout` - delay between heartbeat requests in ms, defaults to `1000`
* `retentionTime` - offset retention time in ms, defaults to 1 day (24 * 3600 * 1000)
* `startingOffset` - starting position (time) when there is no commited offset, defaults to `Kafka.LATEST_OFFSET`
* `recoveryOffset` - recovery position (time) which will used to recover subscription in case of OffsetOutOfRange error, defaults to Kafka.LATEST_OFFSET
* `asyncCompression` - boolean, use asynchronouse decompression instead of synchronous, defaults to `false`
* `handlerConcurrency` - specify concurrency level for the consumer handler function, defaults to 10

## GroupAdmin (consumer groups API)

Offes two methods:

* `listGroups` - list existing consumer groups
* `describeGroup` - describe existing group by its id

Example:

```javascript
var admin = new Kafka.GroupAdmin();

return admin.init().then(function(){
    return admin.listGroups().then(function(groups){
        // [ { groupId: 'no-kafka-admin-test-group', protocolType: 'consumer' } ]
        return admin.describeGroup('no-kafka-admin-test-group').then(function(group){
            /*
            { error: null,
              groupId: 'no-kafka-admin-test-group',
              state: 'Stable',
              protocolType: 'consumer',
              protocol: 'TestStrategy',
              members:
               [ { memberId: 'group-consumer-82646843-b4b8-4e91-94c9-b4708c8b05e8',
                   clientId: 'group-consumer',
                   clientHost: '/192.168.1.4',
                   version: 0,
                   subscriptions: [ 'kafka-test-topic'],
                   metadata: <Buffer 63 6f 6e 73 75 6d 65 72 2d 6d 65 74 61 64 61 74 61>,
                   memberAssignment:
                    { _blength: 44,
                      version: 0,
                      partitionAssignment:
                       [ { topic: 'kafka-test-topic',
                           partitions: [ 0, 1, 2 ] },
                          ],
                      metadata: null } },
                  ] }
             */
        })
    });
});
```

## Compression

__no-kafka__ supports both SNAPPY and Gzip compression.

Enable compression in Producer:

```javascript
var Kafka = require('no-kafka');

var producer = new Kafka.Producer({
    clientId: 'producer',
    codec: Kafka.COMPRESSION_SNAPPY // Kafka.COMPRESSION_NONE, Kafka.COMPRESSION_SNAPPY, Kafka.COMPRESSION_GZIP
});
```

Alternatively just send some messages with specified compression codec (overwrites codec set in contructor):

```javascript
return producer.send({
    topic: 'kafka-test-topic',
    partition: 0,
    message: { value: 'p00' }
}, { codec: Kafka.COMPRESSION_SNAPPY })
```

By default __no-kafka__ will use synchronous compression and decompression (synchronous Gzip is not availble in node < 0.11).
Enable async compression/decompression with `asyncCompression` options:

Producer:

```javascript
var producer = new Kafka.Producer({
    clientId: 'producer',
    asyncCompression: true,
    codec: Kafka.COMPRESSION_SNAPPY
});
```

Consumer:

```javascript
var consumer = new Kafka.SimpleConsumer({
    idleTimeout: 100,
    clientId: 'simple-consumer',
    asyncCompression: true
});
```

## Connection

__no-kafka__ will connect to the hosts specified in `connectionString` constructor option unless it is omitted. In this case it will use KAFKA_URL environment variable or fallback to default `kafka://127.0.0.1:9092`. For better availability always specify several initial brokers: `10.0.1.1:9092,10.0.1.2:9092,10.0.1.3:9092`. The `kafka://` prefix is optional.

All network errors are handled by the library: producer will retry sending failed messages for configured amount of times, simple consumer and group consumer will try to reconnect to failed host, update metadata as needed as so on.

### SSL

Kafka 0.9 supports [encryption and authentication using SSL](http://kafka.apache.org/090/documentation.html#security_ssl).

To connect over SSL, include an `ssl` Object alongside your `connectionString` which contains two properties:
`clientCert` and `clientCertKey`.

If not specified,
these will populate from the `KAFKA_CLIENT_CERT` and `KAFKA_CLIENT_CERT_KEY` environment variables.
The ssl option defaults to `false` if no cert options or environment variables are found.

## Logging

You can differentiate messages from several instances of producer/consumer by providing unique `clientId` in options:

```javascript
var consumer1 = new Kafka.GroupConsumer({
    clientId: 'group-consumer-1'
});
var consumer2 = new Kafka.GroupConsumer({
    clientId: 'group-consumer-2'
});
```
=>

```
2016-01-12T07:41:57.884Z INFO group-consumer-1 ....
2016-01-12T07:41:57.884Z INFO group-consumer-2 ....
```

Change the logging level:

```javascript
var consumer = new Kafka.GroupConsumer({
    clientId: 'group-consumer',
    logger: {
        logLevel: 1 // 0 - nothing, 1 - just errors, 2 - +warnings, 3 - +info, 4 - +debug, 5 - +trace
    }
});
```

Send log messages to Logstash server(s) via UDP:

```javascript
var consumer = new Kafka.GroupConsumer({
    clientId: 'group-consumer',
    logger: {
        logstash: {
            enabled: true,
            connectionString: '10.0.1.1:9999,10.0.1.2:9999',
            app: 'myApp-kafka-consumer'
        }
    }
});
```

You can overwrite the function that outputs messages to stdout/stderr:

```javascript
var consumer = new Kafka.GroupConsumer({
    clientId: 'group-consumer',
    logger: {
        logFunction: console.log
    }
});
```

## Topic Creation

There is no Kafka API call to create a topic. Kafka supports auto creating of topics when their metadata is first requested (`auto.create.topic` option) but the topic is created with all default parameters, which is useless. There is no way to be notified when the topic has been created, so the library will need to ping the server with some interval. There is also no way to be notified of any error for this operation. For this reason, having no guarantees, __no-kafka__ won't provide topic creation method until there will be a specific Kafka API call to create/manage topics.

## License: [MIT](https://github.com/oleksiyk/kafka/blob/master/LICENSE)

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