Maciej Mensfeld edited this page Feb 28, 2018 · 21 revisions

Karafka is a complex tool, that contains multiple configuration options. To keep everything organized, all the configuration options were divided into three groups:

  • Karafka options - options directly related to Karafka framework and it's components
  • Connection pool options - options related to messages producers connection pool
  • Ruby-Kafka driver options - options related to Ruby-Kafka

To apply all those configuration options, you need to use the #setup method from the Karafka::App class (karafka.rb):

class App < Karafka::App
  setup do |config|
    config.client_id = 'my_application'
    config.backend = :inline
    config.batch_fetching = true
    config.batch_consuming = true
    config.kafka.seed_brokers = %w[kafka://]

Note: Karafka allows you to redefine most of the settings per each consumer group, which means that you can have specific custom configuration, that might differ from the default one configured on the app level. This allows you for example, to connect to multiple Kafka clusters.

Karafka configuration options

Option Required Value type Default Description
client_id true String - Application name that will be used as a client_id for Kafka cluster
backend false Symbol :inline Backend for consumption that we want to use (currently :inline or :sidekiq)
logger false Object Logger Logger instance
monitor false Object Monitor Monitor instance
consumer_mapper false Module Routing::ConsumerMapper Mapper for building consumer ids
topic_mapper false Module Routing::TopicMapper Mapper for hiding Kafka provider specific topic prefixes/postfixes, so internaly we use "pure" topics
parser false Module Karafka::Parsers::Json Default parser that will be used to parse and serialize both incoming and outgoing data
batch_fetching false Boolean true Should the incoming messages be fetched in batches, or one at a time
batch_consuming false Boolean false Should the incoming messages be consumed/processed in batches, or one at a time
persistent false Boolean true Should we operate in a single consumer instance across batches or create instance per batch
shutdown_timeout false Integer, nil 60 The number of seconds after which Karafka longer waits for the consumers to stop gracefully
params_base_class false Class Hash Base class for the dynamically built Karafka::Params::Params class. See Wiki for more details

Ruby-Kafka driver configuration options

We've listed here only the most important configuration options. If you're interested in all the options, please go to the config.rb file for more details.

Option Required Value type Default Description
kafka.seed_brokers true Array - Kafka server hosts. Karafka will discover whole cluster structure automatically
kafka.start_from_beginning false Boolean true Consume messages starting at the beginning or consume new messages that are produced at first run
kafka.offset_commit_interval false Integer 10 The interval between offset commits in seconds
kafka.offset_commit_threshold false Integer 0 The number of messages that can be consume before their offsets are committed
kafka.heartbeat_interval false Integer 10 The interval between heartbeats
kafka.ssl_ca_cert false String nil SSL CA certificate
kafka.ssl_client_cert false String nil SSL client certificate
kafka.ssl_client_cert_key false String nil SSL client certificate password
kafka.ssl_ca_certs_from_system false Boolean false Use the CA certs from your system's default

External components configurators

For additional setup and/or configuration tasks you can use the #after_init callback hooks. It is executed once per process, right after all the framework components are ready (including those dynamically built). It can be used for example to configure some external components that can be based on Karafka internal settings.

class App < Karafka::App
  # Setup and other things...

  # Once everything is loaded and done, assign Karafka app logger as a Sidekiq logger
  # @note This example does not use config details, but you can use all the config values
  #   to setup your external components
  after_init do |_config|
    Sidekiq::Logging.logger = Karafka::App.logger

Environment variables settings

There are several env settings you can use:

ENV name Default Description
KARAFKA_ENV development In what mode this application should boot (production/development/test/etc)
KARAFKA_BOOT_FILE app_root/karafka.rb Path to a file that contains Karafka app configuration and booting procedures

Kafka brokers auto-discovery

Karafka supports Kafka brokers auto-discovery during startup and on failures. You need to provide at least one Kafka broker, from which the entire Kafka cluster will be discovered. Karafka will refresh list of available brokers if something goes wrong. This allows it to be aware of changes that happen in the infrastructure (adding and removing nodes).

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