Class: Kafka::Client

Inherits:
Object
  • Object
show all
Defined in:
lib/kafka/client.rb

Instance Method Summary collapse

Constructor Details

#initialize(seed_brokers:, client_id: "ruby-kafka", logger: nil, connect_timeout: nil, socket_timeout: nil, ssl_ca_cert_file_path: nil, ssl_ca_cert: nil, ssl_client_cert: nil, ssl_client_cert_key: nil, ssl_client_cert_key_password: nil, ssl_client_cert_chain: nil, sasl_gssapi_principal: nil, sasl_gssapi_keytab: nil, sasl_plain_authzid: '', sasl_plain_username: nil, sasl_plain_password: nil, sasl_scram_username: nil, sasl_scram_password: nil, sasl_scram_mechanism: nil, sasl_aws_msk_iam_access_key_id: nil, sasl_aws_msk_iam_secret_key_id: nil, sasl_aws_msk_iam_aws_region: nil, sasl_over_ssl: true, ssl_ca_certs_from_system: false, partitioner: nil, sasl_oauth_token_provider: nil, ssl_verify_hostname: true, resolve_seed_brokers: false) ⇒ Client

Initializes a new Kafka client.

Parameters:

  • seed_brokers (Array<String>, String) —

    the list of brokers used to initialize the client. Either an Array of connections, or a comma separated string of connections. A connection can either be a string of "host:port" or a full URI with a scheme. If there's a scheme it's ignored and only host/port are used.

  • client_id (String) (defaults to: "ruby-kafka") —

    the identifier for this application.

  • logger (Logger) (defaults to: nil) —

    the logger that should be used by the client.

  • connect_timeout (Integer, nil) (defaults to: nil) —

    the timeout setting for connecting to brokers. See BrokerPool#initialize.

  • socket_timeout (Integer, nil) (defaults to: nil) —

    the timeout setting for socket connections. See BrokerPool#initialize.

  • ssl_ca_cert (String, Array<String>, nil) (defaults to: nil) —

    a PEM encoded CA cert, or an Array of PEM encoded CA certs, to use with an SSL connection.

  • ssl_ca_cert_file_path (String, Array<String>, nil) (defaults to: nil) —

    a path on the filesystem, or an Array of paths, to PEM encoded CA cert(s) to use with an SSL connection.

  • ssl_client_cert (String, nil) (defaults to: nil) —

    a PEM encoded client cert to use with an SSL connection. Must be used in combination with ssl_client_cert_key.

  • ssl_client_cert_key (String, nil) (defaults to: nil) —

    a PEM encoded client cert key to use with an SSL connection. Must be used in combination with ssl_client_cert.

  • ssl_client_cert_key_password (String, nil) (defaults to: nil) —

    the password required to read the ssl_client_cert_key. Must be used in combination with ssl_client_cert_key.

  • sasl_gssapi_principal (String, nil) (defaults to: nil) —

    a KRB5 principal

  • sasl_gssapi_keytab (String, nil) (defaults to: nil) —

    a KRB5 keytab filepath

  • sasl_scram_username (String, nil) (defaults to: nil) —

    SCRAM username

  • sasl_scram_password (String, nil) (defaults to: nil) —

    SCRAM password

  • sasl_scram_mechanism (String, nil) (defaults to: nil) —

    Scram mechanism, either "sha256" or "sha512"

  • sasl_over_ssl (Boolean) (defaults to: true) —

    whether to enforce SSL with SASL

  • ssl_ca_certs_from_system (Boolean) (defaults to: false) —

    whether to use the CA certs from the system's default certificate store.

  • partitioner (Partitioner, nil) (defaults to: nil) —

    the partitioner that should be used by the client.

  • sasl_oauth_token_provider (Object, nil) (defaults to: nil) —

    OAuthBearer Token Provider instance that implements method token. See Sasl::OAuth#initialize

  • ssl_verify_hostname (Boolean, true) (defaults to: true) —

    whether to verify that the host serving the SSL certificate and the signing chain of the certificate have the correct domains based on the CA certificate

  • resolve_seed_brokers (Boolean) (defaults to: false) —

    whether to resolve each hostname of the seed brokers. If a broker is resolved to multiple IP addresses, the client tries to connect to each of the addresses until it can connect.



83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
 
# File 'lib/kafka/client.rb', line 83

def initialize(seed_brokers:, client_id: "ruby-kafka", logger: nil, connect_timeout: nil, socket_timeout: nil,
               ssl_ca_cert_file_path: nil, ssl_ca_cert: nil, ssl_client_cert: nil, ssl_client_cert_key: nil,
               ssl_client_cert_key_password: nil, ssl_client_cert_chain: nil, sasl_gssapi_principal: nil,
               sasl_gssapi_keytab: nil, sasl_plain_authzid: '', sasl_plain_username: nil, sasl_plain_password: nil,
               sasl_scram_username: nil, sasl_scram_password: nil, sasl_scram_mechanism: nil,
               sasl_aws_msk_iam_access_key_id: nil,
               sasl_aws_msk_iam_secret_key_id: nil, sasl_aws_msk_iam_aws_region: nil,
               sasl_over_ssl: true, ssl_ca_certs_from_system: false, partitioner: nil, sasl_oauth_token_provider: nil, ssl_verify_hostname: true,
               resolve_seed_brokers: false)
  @logger = TaggedLogger.new(logger)
  @instrumenter = Instrumenter.new(client_id: client_id)
  @seed_brokers = normalize_seed_brokers(seed_brokers)
  @resolve_seed_brokers = resolve_seed_brokers

  ssl_context = SslContext.build(
    ca_cert_file_path: ssl_ca_cert_file_path,
    ca_cert: ssl_ca_cert,
    client_cert: ssl_client_cert,
    client_cert_key: ssl_client_cert_key,
    client_cert_key_password: ssl_client_cert_key_password,
    client_cert_chain: ssl_client_cert_chain,
    ca_certs_from_system: ssl_ca_certs_from_system,
    verify_hostname: ssl_verify_hostname
  )

  sasl_authenticator = SaslAuthenticator.new(
    sasl_gssapi_principal: sasl_gssapi_principal,
    sasl_gssapi_keytab: sasl_gssapi_keytab,
    sasl_plain_authzid: sasl_plain_authzid,
    sasl_plain_username: sasl_plain_username,
    sasl_plain_password: sasl_plain_password,
    sasl_scram_username: sasl_scram_username,
    sasl_scram_password: sasl_scram_password,
    sasl_scram_mechanism: sasl_scram_mechanism,
    sasl_aws_msk_iam_access_key_id: sasl_aws_msk_iam_access_key_id,
    sasl_aws_msk_iam_secret_key_id: sasl_aws_msk_iam_secret_key_id,
    sasl_aws_msk_iam_aws_region: sasl_aws_msk_iam_aws_region,
    sasl_oauth_token_provider: sasl_oauth_token_provider,
    logger: @logger
  )

  if sasl_authenticator.enabled? && sasl_over_ssl && ssl_context.nil?
    raise ArgumentError, "SASL authentication requires that SSL is configured"
  end

  @connection_builder = ConnectionBuilder.new(
    client_id: client_id,
    connect_timeout: connect_timeout,
    socket_timeout: socket_timeout,
    ssl_context: ssl_context,
    logger: @logger,
    instrumenter: @instrumenter,
    sasl_authenticator: sasl_authenticator
  )

  @cluster = initialize_cluster
  @partitioner = partitioner || Partitioner.new
end

Instance Method Details

#alter_configs(broker_id, configs = []) ⇒ nil

Alter broker configs

Parameters:

  • broker_id (int) —

    the id of the broker

  • configs (Array) (defaults to: []) —

    array of config strings.

Returns:

  • (nil) 


595
596
597
 
# File 'lib/kafka/client.rb', line 595

def alter_configs(broker_id, configs = [])
  @cluster.alter_configs(broker_id, configs)
end

#alter_topic(name, configs = {}) ⇒ nil

Note:

This is an alpha level API and is subject to change.

Alter the configuration of a topic.

Configuration keys must match Kafka's topic-level configs.

Examples:

Describing the cleanup policy config of a topic

kafka = Kafka.new(["kafka1:9092"])
kafka.alter_topic("my-topic", "cleanup.policy" => "delete", "max.message.byte" => "100000")

Parameters:

  • name (String) —

    the name of the topic.

  • configs (Hash<String, String>) (defaults to: {}) —

    hash of desired config keys and values.

Returns:

  • (nil) 


672
673
674
 
# File 'lib/kafka/client.rb', line 672

def alter_topic(name, configs = {})
  @cluster.alter_topic(name, configs)
end

#apis ⇒ Object 



789
790
791
 
# File 'lib/kafka/client.rb', line 789

def apis
  @cluster.apis
end

#async_producer(delivery_interval: 0, delivery_threshold: 0, max_queue_size: 1000, max_retries: -1,, retry_backoff: 0, **options) ⇒ AsyncProducer

Creates a new AsyncProducer instance.

All parameters allowed by #producer can be passed. In addition to this, a few extra parameters can be passed when creating an async producer.

Parameters:

  • max_queue_size (Integer) (defaults to: 1000) —

    the maximum number of messages allowed in the queue.

  • delivery_threshold (Integer) (defaults to: 0) —

    if greater than zero, the number of buffered messages that will automatically trigger a delivery.

  • delivery_interval (Integer) (defaults to: 0) —

    if greater than zero, the number of seconds between automatic message deliveries.

Returns:

See Also:



337
338
339
340
341
342
343
344
345
346
347
348
349
350
 
# File 'lib/kafka/client.rb', line 337

def async_producer(delivery_interval: 0, delivery_threshold: 0, max_queue_size: 1000, max_retries: -1, retry_backoff: 0, **options)
  sync_producer = producer(**options)

  AsyncProducer.new(
    sync_producer: sync_producer,
    delivery_interval: delivery_interval,
    delivery_threshold: delivery_threshold,
    max_queue_size: max_queue_size,
    max_retries: max_retries,
    retry_backoff: retry_backoff,
    instrumenter: @instrumenter,
    logger: @logger,
  )
end

#brokers ⇒ Array<Kafka::BrokerInfo>

List all brokers in the cluster.

Returns:



796
797
798
 
# File 'lib/kafka/client.rb', line 796

def brokers
  @cluster.cluster_info.brokers
end

#close ⇒ nil

Closes all connections to the Kafka brokers and frees up used resources.

Returns:

  • (nil) 


810
811
812
 
# File 'lib/kafka/client.rb', line 810

def close
  @cluster.disconnect
end

#consumer(group_id:, session_timeout: 30, rebalance_timeout: 60, offset_commit_interval: 10, offset_commit_threshold: 0, heartbeat_interval: 10, offset_retention_time: nil, fetcher_max_queue_size: 100, refresh_topic_interval: 0, interceptors: [], assignment_strategy: nil) ⇒ Consumer

Creates a new Kafka consumer.

Parameters:

  • group_id (String) —

    the id of the group that the consumer should join.

  • session_timeout (Integer) (defaults to: 30) —

    the number of seconds after which, if a client hasn't contacted the Kafka cluster, it will be kicked out of the group.

  • offset_commit_interval (Integer) (defaults to: 10) —

    the interval between offset commits, in seconds.

  • offset_commit_threshold (Integer) (defaults to: 0) —

    the number of messages that can be processed before their offsets are committed. If zero, offset commits are not triggered by message processing.

  • heartbeat_interval (Integer) (defaults to: 10) —

    the interval between heartbeats; must be less than the session window.

  • offset_retention_time (Integer) (defaults to: nil) —

    the time period that committed offsets will be retained, in seconds. Defaults to the broker setting.

  • fetcher_max_queue_size (Integer) (defaults to: 100) —

    max number of items in the fetch queue that are stored for further processing. Note, that each item in the queue represents a response from a single broker.

  • refresh_topic_interval (Integer) (defaults to: 0) —

    interval of refreshing the topic list. If it is 0, the topic list won't be refreshed (default) If it is n (n > 0), the topic list will be refreshed every n seconds

  • interceptors (Array<Object>) (defaults to: []) —

    a list of consumer interceptors that implement call(Kafka::FetchedBatch).

  • assignment_strategy (Object) (defaults to: nil) —

    a partition assignment strategy that implements protocol_type(), user_data(), and assign(members:, partitions:)

Returns:



377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
 
# File 'lib/kafka/client.rb', line 377

def consumer(
    group_id:,
    session_timeout: 30,
    rebalance_timeout: 60,
    offset_commit_interval: 10,
    offset_commit_threshold: 0,
    heartbeat_interval: 10,
    offset_retention_time: nil,
    fetcher_max_queue_size: 100,
    refresh_topic_interval: 0,
    interceptors: [],
    assignment_strategy: nil
)
  cluster = initialize_cluster

  instrumenter = DecoratingInstrumenter.new(@instrumenter, {
    group_id: group_id,
  })

  # The Kafka protocol expects the retention time to be in ms.
  retention_time = (offset_retention_time && offset_retention_time * 1_000) || -1

  group = ConsumerGroup.new(
    cluster: cluster,
    logger: @logger,
    group_id: group_id,
    session_timeout: session_timeout,
    rebalance_timeout: rebalance_timeout,
    retention_time: retention_time,
    instrumenter: instrumenter,
    assignment_strategy: assignment_strategy
  )

  fetcher = Fetcher.new(
    cluster: initialize_cluster,
    group: group,
    logger: @logger,
    instrumenter: instrumenter,
    max_queue_size: fetcher_max_queue_size
  )

  offset_manager = OffsetManager.new(
    cluster: cluster,
    group: group,
    fetcher: fetcher,
    logger: @logger,
    commit_interval: offset_commit_interval,
    commit_threshold: offset_commit_threshold,
    offset_retention_time: offset_retention_time
  )

  heartbeat = Heartbeat.new(
    group: group,
    interval: heartbeat_interval,
    instrumenter: instrumenter
  )

  Consumer.new(
    cluster: cluster,
    logger: @logger,
    instrumenter: instrumenter,
    group: group,
    offset_manager: offset_manager,
    fetcher: fetcher,
    session_timeout: session_timeout,
    heartbeat: heartbeat,
    refresh_topic_interval: refresh_topic_interval,
    interceptors: interceptors
  )
end

#controller_broker ⇒ Kafka::BrokerInfo

The current controller broker in the cluster.

Returns:



803
804
805
 
# File 'lib/kafka/client.rb', line 803

def controller_broker
  brokers.find {|broker| broker.node_id == @cluster.cluster_info.controller_id }
end

#create_partitions_for(name, num_partitions: 1, timeout: 30) ⇒ nil

Create partitions for a topic.

the topic partitions to be added.

Parameters:

  • name (String) —

    the name of the topic.

  • num_partitions (Integer) (defaults to: 1) —

    the number of desired partitions for

  • timeout (Integer) (defaults to: 30) —

    a duration of time to wait for the new

Returns:

  • (nil) 


700
701
702
 
# File 'lib/kafka/client.rb', line 700

def create_partitions_for(name, num_partitions: 1, timeout: 30)
  @cluster.create_partitions_for(name, num_partitions: num_partitions, timeout: timeout)
end

#create_topic(name, num_partitions: 1, replication_factor: 1, timeout: 30, config: {}) ⇒ nil

Creates a topic in the cluster.

Examples:

Creating a topic with log compaction

# Enable log compaction:
config = { "cleanup.policy" => "compact" }

# Create the topic:
kafka.create_topic("dns-mappings", config: config)

Parameters:

  • name (String) —

    the name of the topic.

  • num_partitions (Integer) (defaults to: 1) —

    the number of partitions that should be created in the topic.

  • replication_factor (Integer) (defaults to: 1) —

    the replication factor of the topic.

  • timeout (Integer) (defaults to: 30) —

    a duration of time to wait for the topic to be completely created.

  • config (Hash) (defaults to: {}) —

    topic configuration entries. See the Kafka documentation for more information.

Returns:

  • (nil)

Raises:



619
620
621
622
623
624
625
626
627
 
# File 'lib/kafka/client.rb', line 619

def create_topic(name, num_partitions: 1, replication_factor: 1, timeout: 30, config: {})
  @cluster.create_topic(
    name,
    num_partitions: num_partitions,
    replication_factor: replication_factor,
    timeout: timeout,
    config: config,
  )
end

#delete_topic(name, timeout: 30) ⇒ nil

Delete a topic in the cluster.

Parameters:

  • name (String) —

    the name of the topic.

  • timeout (Integer) (defaults to: 30) —

    a duration of time to wait for the topic to be completely marked deleted.

Returns:

  • (nil) 


635
636
637
 
# File 'lib/kafka/client.rb', line 635

def delete_topic(name, timeout: 30)
  @cluster.delete_topic(name, timeout: timeout)
end

#deliver_message(value, key: nil, headers: {}, topic:, partition: nil, partition_key: nil, retries: 1) ⇒ nil

Delivers a single message to the Kafka cluster.

Note: Only use this API for low-throughput scenarios. If you want to deliver many messages at a high rate, or if you want to configure the way messages are sent, use the #producer or #async_producer APIs instead.

Parameters:

  • value (String, nil) —

    the message value.

  • key (String, nil) (defaults to: nil) —

    the message key.

  • headers (Hash<String, String>) (defaults to: {}) —

    the headers for the message.

  • topic (String) —

    the topic that the message should be written to.

  • partition (Integer, nil) (defaults to: nil) —

    the partition that the message should be written to, or nil if either partition_key is passed or the partition should be chosen at random.

  • partition_key (String) (defaults to: nil) —

    a value used to deterministically choose a partition to write to.

  • retries (Integer) (defaults to: 1) —

    the number of times to retry the delivery before giving up.

Returns:

  • (nil) 


160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
 
# File 'lib/kafka/client.rb', line 160

def deliver_message(value, key: nil, headers: {}, topic:, partition: nil, partition_key: nil, retries: 1)
  create_time = Time.now

  # We want to fail fast if `topic` isn't a String
  topic = topic.to_str

  message = PendingMessage.new(
    value: value,
    key: key,
    headers: headers,
    topic: topic,
    partition: partition,
    partition_key: partition_key,
    create_time: create_time
  )

  if partition.nil?
    partition_count = @cluster.partitions_for(topic).count
    partition = @partitioner.call(partition_count, message)
  end

  buffer = MessageBuffer.new

  buffer.write(
    value: message.value,
    key: message.key,
    headers: message.headers,
    topic: message.topic,
    partition: partition,
    create_time: message.create_time,
  )

  @cluster.add_target_topics([topic])

  compressor = Compressor.new(
    instrumenter: @instrumenter,
  )

  transaction_manager = TransactionManager.new(
    cluster: @cluster,
    logger: @logger,
    idempotent: false,
    transactional: false
  )

  operation = ProduceOperation.new(
    cluster: @cluster,
    transaction_manager: transaction_manager,
    buffer: buffer,
    required_acks: 1,
    ack_timeout: 10,
    compressor: compressor,
    logger: @logger,
    instrumenter: @instrumenter,
  )

  attempt = 1

  begin
    @cluster.refresh_metadata_if_necessary!

    operation.execute

    unless buffer.empty?
      raise DeliveryFailed.new(nil, [message])
    end
  rescue Kafka::Error => e
    @cluster.mark_as_stale!

    if attempt >= (retries + 1)
      raise
    else
      attempt += 1
      @logger.warn "Error while delivering message, #{e.class}: #{e.message}; retrying after 1s..."

      sleep 1

      retry
    end
  end
end

#describe_configs(broker_id, configs = []) ⇒ Array<Kafka::Protocol::DescribeConfigsResponse::ConfigEntry>

Describe broker configs

Parameters:

  • broker_id (int) —

    the id of the broker

  • configs (Array) (defaults to: []) —

    array of config keys.

Returns:



586
587
588
 
# File 'lib/kafka/client.rb', line 586

def describe_configs(broker_id, configs = [])
  @cluster.describe_configs(broker_id, configs)
end

#describe_group(group_id) ⇒ Kafka::Protocol::DescribeGroupsResponse::Group

Describe a consumer group

Parameters:

  • group_id (String) —

    the id of the consumer group

Returns:



680
681
682
 
# File 'lib/kafka/client.rb', line 680

def describe_group(group_id)
  @cluster.describe_group(group_id)
end

#describe_topic(name, configs = []) ⇒ Hash<String, String>

Note:

This is an alpha level API and is subject to change.

Describe the configuration of a topic.

Retrieves the topic configuration from the Kafka brokers. Configuration names refer to Kafka's topic-level configs.

Examples:

Describing the cleanup policy config of a topic

kafka = Kafka.new(["kafka1:9092"])
kafka.describe_topic("my-topic", ["cleanup.policy"])
#=> { "cleanup.policy" => "delete" }

Parameters:

  • name (String) —

    the name of the topic.

  • configs (Array<String>) (defaults to: []) —

    array of desired config names.

Returns:

  • (Hash<String, String>) 


654
655
656
 
# File 'lib/kafka/client.rb', line 654

def describe_topic(name, configs = [])
  @cluster.describe_topic(name, configs)
end

#each_message(topic:, start_from_beginning: true, max_wait_time: 5, min_bytes: 1, max_bytes: 1048576, &block) ⇒ nil

Enumerate all messages in a topic.

Parameters:

  • topic (String) —

    the topic to consume messages from.

  • start_from_beginning (Boolean) (defaults to: true) —

    whether to start from the beginning of the topic or just subscribe to new messages being produced.

  • max_wait_time (Integer) (defaults to: 5) —

    the maximum amount of time to wait before the server responds, in seconds.

  • min_bytes (Integer) (defaults to: 1) —

    the minimum number of bytes to wait for. If set to zero, the broker will respond immediately, but the response may be empty. The default is 1 byte, which means that the broker will respond as soon as a message is written to the partition.

  • max_bytes (Integer) (defaults to: 1048576) —

    the maximum number of bytes to include in the response message set. Default is 1 MB. You need to set this higher if you expect messages to be larger than this.

Returns:

  • (nil) 


555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
 
# File 'lib/kafka/client.rb', line 555

def each_message(topic:, start_from_beginning: true, max_wait_time: 5, min_bytes: 1, max_bytes: 1048576, &block)
  default_offset ||= start_from_beginning ? :earliest : :latest
  offsets = Hash.new { default_offset }

  loop do
    operation = FetchOperation.new(
      cluster: @cluster,
      logger: @logger,
      min_bytes: min_bytes,
      max_wait_time: max_wait_time,
    )

    @cluster.partitions_for(topic).map(&:partition_id).each do |partition|
      partition_offset = offsets[partition]
      operation.fetch_from_partition(topic, partition, offset: partition_offset, max_bytes: max_bytes)
    end

    batches = operation.execute

    batches.each do |batch|
      batch.messages.each(&block)
      offsets[batch.partition] = batch.last_offset + 1 unless batch.unknown_last_offset?
    end
  end
end

#fetch_group_offsets(group_id) ⇒ Hash<String, Hash<Integer, Kafka::Protocol::OffsetFetchResponse::PartitionOffsetInfo>>

Fetch all committed offsets for a consumer group

Parameters:

  • group_id (String) —

    the id of the consumer group

Returns:



688
689
690
 
# File 'lib/kafka/client.rb', line 688

def fetch_group_offsets(group_id)
  @cluster.fetch_group_offsets(group_id)
end

#fetch_messages(topic:, partition:, offset: :latest, max_wait_time: 5, min_bytes: 1, max_bytes: 1048576, retries: 1) ⇒ Array<Kafka::FetchedMessage>

Fetches a batch of messages from a single partition. Note that it's possible to get back empty batches.

The starting point for the fetch can be configured with the :offset argument. If you pass a number, the fetch will start at that offset. However, there are two special Symbol values that can be passed instead:

  • :earliest — the first offset in the partition.
  • :latest — the next offset that will be written to, effectively making the call block until there is a new message in the partition.

The Kafka protocol specifies the numeric values of these two options: -2 and -1, respectively. You can also pass in these numbers directly.

Example

When enumerating the messages in a partition, you typically fetch batches sequentially.

offset = :earliest

loop do
  messages = kafka.fetch_messages(
    topic: "my-topic",
    partition: 42,
    offset: offset,
  )

  messages.each do |message|
    puts message.offset, message.key, message.value

    # Set the next offset that should be read to be the subsequent
    # offset.
    offset = message.offset + 1
  end
end

See a working example in examples/simple-consumer.rb.

Parameters:

  • topic (String) —

    the topic that messages should be fetched from.

  • partition (Integer) —

    the partition that messages should be fetched from.

  • offset (Integer, Symbol) (defaults to: :latest) —

    the offset to start reading from. Default is the latest offset.

  • max_wait_time (Integer) (defaults to: 5) —

    the maximum amount of time to wait before the server responds, in seconds.

  • min_bytes (Integer) (defaults to: 1) —

    the minimum number of bytes to wait for. If set to zero, the broker will respond immediately, but the response may be empty. The default is 1 byte, which means that the broker will respond as soon as a message is written to the partition.

  • max_bytes (Integer) (defaults to: 1048576) —

    the maximum number of bytes to include in the response message set. Default is 1 MB. You need to set this higher if you expect messages to be larger than this.

Returns:



507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
 
# File 'lib/kafka/client.rb', line 507

def fetch_messages(topic:, partition:, offset: :latest, max_wait_time: 5, min_bytes: 1, max_bytes: 1048576, retries: 1)
  operation = FetchOperation.new(
    cluster: @cluster,
    logger: @logger,
    min_bytes: min_bytes,
    max_bytes: max_bytes,
    max_wait_time: max_wait_time,
  )

  operation.fetch_from_partition(topic, partition, offset: offset, max_bytes: max_bytes)

  attempt = 1

  begin
    operation.execute.flat_map {|batch| batch.messages }
  rescue Kafka::Error => e
    @cluster.mark_as_stale!

    if attempt >= (retries + 1)
      raise
    else
      attempt += 1
      @logger.warn "Error while fetching messages, #{e.class}: #{e.message}; retrying..."
      retry
    end
  end
end

#groups ⇒ Array<String>

Lists all consumer groups in the cluster

Returns:

  • (Array<String>) —

    the list of group ids



722
723
724
 
# File 'lib/kafka/client.rb', line 722

def groups
  @cluster.list_groups
end

#has_topic?(topic) ⇒ Boolean

Returns:

  • (Boolean) 


726
727
728
729
730
 
# File 'lib/kafka/client.rb', line 726

def has_topic?(topic)
  @cluster.clear_target_topics
  @cluster.add_target_topics([topic])
  @cluster.topics.include?(topic)
end

#last_offset_for(topic, partition) ⇒ Integer

Retrieve the offset of the last message in a partition. If there are no messages in the partition -1 is returned.

Parameters:

  • topic (String)
  • partition (Integer)

Returns:

  • (Integer) —

    the offset of the last message in the partition, or -1 if there are no messages in the partition.



755
756
757
758
759
 
# File 'lib/kafka/client.rb', line 755

def last_offset_for(topic, partition)
  # The offset resolution API will return the offset of the "next" message to
  # be written when resolving the "latest" offset, so we subtract one.
  @cluster.resolve_offset(topic, partition, :latest) - 1
end

#last_offsets_for(*topics) ⇒ Hash<String, Hash<Integer, Integer>>

Retrieve the offset of the last message in each partition of the specified topics.

Examples:

last_offsets_for('topic-1', 'topic-2') # =>
# {
#   'topic-1' => { 0 => 100, 1 => 100 },
#   'topic-2' => { 0 => 100, 1 => 100 }
# }

Parameters:

  • topics (Array<String>) —

    topic names.

Returns:

  • (Hash<String, Hash<Integer, Integer>>) 


771
772
773
774
775
776
777
778
 
# File 'lib/kafka/client.rb', line 771

def last_offsets_for(*topics)
  @cluster.add_target_topics(topics)
  topics.map {|topic|
    partition_ids = @cluster.partitions_for(topic).collect(&:partition_id)
    partition_offsets = @cluster.resolve_offsets(topic, partition_ids, :latest)
    [topic, partition_offsets.collect { |k, v| [k, v - 1] }.to_h]
  }.to_h
end

#partitions_for(topic) ⇒ Integer

Counts the number of partitions in a topic.

Parameters:

  • topic (String)

Returns:

  • (Integer) —

    the number of partitions in the topic.



736
737
738
 
# File 'lib/kafka/client.rb', line 736

def partitions_for(topic)
  @cluster.partitions_for(topic).count
end

#producer(compression_codec: nil, compression_threshold: 1, ack_timeout: 5, required_acks: :all, max_retries: 2, retry_backoff: 1, max_buffer_size: 1000, max_buffer_bytesize: 10_000_000, idempotent: false, transactional: false, transactional_id: nil, transactional_timeout: 60, interceptors: []) ⇒ Kafka::Producer

Initializes a new Kafka producer.

Parameters:

  • ack_timeout (Integer) (defaults to: 5) —

    The number of seconds a broker can wait for replicas to acknowledge a write before responding with a timeout.

  • required_acks (Integer, Symbol) (defaults to: :all) —

    The number of replicas that must acknowledge a write, or :all if all in-sync replicas must acknowledge.

  • max_retries (Integer) (defaults to: 2) —

    the number of retries that should be attempted before giving up sending messages to the cluster. Does not include the original attempt.

  • retry_backoff (Integer) (defaults to: 1) —

    the number of seconds to wait between retries.

  • max_buffer_size (Integer) (defaults to: 1000) —

    the number of messages allowed in the buffer before new writes will raise BufferOverflow exceptions.

  • max_buffer_bytesize (Integer) (defaults to: 10_000_000) —

    the maximum size of the buffer in bytes. attempting to produce messages when the buffer reaches this size will result in BufferOverflow being raised.

  • compression_codec (Symbol, nil) (defaults to: nil) —

    the name of the compression codec to use, or nil if no compression should be performed. Valid codecs: :snappy, :gzip, :lz4, :zstd

  • compression_threshold (Integer) (defaults to: 1) —

    the number of messages that needs to be in a message set before it should be compressed. Note that message sets are per-partition rather than per-topic or per-producer.

  • interceptors (Array<Object>) (defaults to: []) —

    a list of producer interceptors the implement call(Kafka::PendingMessage).

Returns:



275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
 
# File 'lib/kafka/client.rb', line 275

def producer(
  compression_codec: nil,
  compression_threshold: 1,
  ack_timeout: 5,
  required_acks: :all,
  max_retries: 2,
  retry_backoff: 1,
  max_buffer_size: 1000,
  max_buffer_bytesize: 10_000_000,
  idempotent: false,
  transactional: false,
  transactional_id: nil,
  transactional_timeout: 60,
  interceptors: []
)
  cluster = initialize_cluster
  compressor = Compressor.new(
    codec_name: compression_codec,
    threshold: compression_threshold,
    instrumenter: @instrumenter,
  )

  transaction_manager = TransactionManager.new(
    cluster: cluster,
    logger: @logger,
    idempotent: idempotent,
    transactional: transactional,
    transactional_id: transactional_id,
    transactional_timeout: transactional_timeout,
  )

  Producer.new(
    cluster: cluster,
    transaction_manager: transaction_manager,
    logger: @logger,
    instrumenter: @instrumenter,
    compressor: compressor,
    ack_timeout: ack_timeout,
    required_acks: required_acks,
    max_retries: max_retries,
    retry_backoff: retry_backoff,
    max_buffer_size: max_buffer_size,
    max_buffer_bytesize: max_buffer_bytesize,
    partitioner: @partitioner,
    interceptors: interceptors
  )
end

#replica_count_for(topic) ⇒ Integer

Counts the number of replicas for a topic's partition

Parameters:

  • topic (String)

Returns:

  • (Integer) —

    the number of replica nodes for the topic's partition



744
745
746
 
# File 'lib/kafka/client.rb', line 744

def replica_count_for(topic)
  @cluster.partitions_for(topic).first.replicas.count
end

#supports_api?(api_key, version = nil) ⇒ Boolean

Check whether current cluster supports a specific version or not

Parameters:

  • api_key (Integer) —

    API key.

  • version (Integer) (defaults to: nil) —

    API version.

Returns:

  • (Boolean) 


785
786
787
 
# File 'lib/kafka/client.rb', line 785

def supports_api?(api_key, version = nil)
  @cluster.supports_api?(api_key, version)
end

#topics ⇒ Array<String>

Lists all topics in the cluster.

Returns:

  • (Array<String>) —

    the list of topic names.



707
708
709
710
711
712
713
714
715
716
717
 
# File 'lib/kafka/client.rb', line 707

def topics
  attempts = 0
  begin
    attempts += 1
    @cluster.list_topics
  rescue Kafka::ConnectionError
    @cluster.mark_as_stale!
    retry unless attempts > 1
    raise
  end
end