CONFIGURATION.md

Configuration

Deimos supports a succinct, readable syntax which uses pure Ruby to allow flexible configuration.

You can access any configuration value via a simple Deimos.config.whatever.

Nested configuration is denoted in simple dot notation: kafka.ssl.enabled. Headings below will follow the nested configurations.

Base Configuration

Config name	Default	Description
logger	Logger.new(STDOUT)	The logger that Deimos will use.
phobos_logger	Deimos.config.logger	The logger passed to Phobos.
metrics	Deimos::Metrics::Mock.new	The metrics backend use for reporting.
tracer	Deimos::Tracer::Mock.new	The tracer backend used for debugging.

Defining Producers

You can define a new producer thusly:

Deimos.configure do
  producer do
    class_name 'MyProducer'
    topic 'MyTopic'
    schema 'MyTopicSchema'
    namespace 'my.namespace'
    key_config field: :id

  # If config.schema.path is app/schemas, assumes there is a file in
  # app/schemas/my/namespace/MyTopicSchema.avsc
  end
end

You can have as many producer blocks as you like to define more producers.

Config name	Default	Description
class_name	nil	Class name of the producer class (subclass of Deimos::Producer.)
topic	nil	Topic to produce to.
schema	nil	Name of the schema to use to encode data before producing.
namespace	nil	Namespace of the schema to use when finding it locally.
key_config	nil	Configuration hash for message keys. See Kafka Message Keys

Defining Consumers

Consumers are defined almost identically to producers:

Deimos.configure do
  consumer do
    class_name 'MyConsumer'
    topic 'MyTopic'
    schema 'MyTopicSchema'
    namespace 'my.namespace'
    key_config field: :id

    # Setting to :inline_batch will invoke consume_batch instead of consume
    # for each batch of messages.
    delivery :batch

  # If config.schema.path is app/schemas, assumes there is a file in
  # app/schemas/my/namespace/MyTopicSchema.avsc
  end
end

In addition to the producer configs, you can define a number of overrides to the basic consumer configuration for each consumer. This is analogous to the listener config in phobos.yml.

Config name	Default	Description
class_name	nil	Class name of the consumer class (subclass of Deimos::Consumer.)
topic	nil	Topic to produce to.
schema	nil	This is optional but strongly recommended for testing purposes; this will validate against a local schema file used as the reader schema, as well as being able to write tests against this schema. This is recommended since it ensures you are always getting the values you expect.
namespace	nil	Namespace of the schema to use when finding it locally.
key_config	nil	Configuration hash for message keys. See Kafka Message Keys
group_id	nil	ID of the consumer group.
max_concurrency	1	Number of threads created for this listener. Each thread will behave as an independent consumer. They don't share any state.
start_from_beginning	true	Once the consumer group has checkpointed its progress in the topic's partitions, the consumers will always start from the checkpointed offsets, regardless of config. As such, this setting only applies when the consumer initially starts consuming from a topic
max_bytes_per_partition	512.kilobytes	Maximum amount of data fetched from a single partition at a time.
min_bytes	1	Minimum number of bytes to read before returning messages from the server; if max_wait_time is reached, this is ignored.
max_wait_time	5	Maximum duration of time to wait before returning messages from the server, in seconds.
force_encoding	nil	Apply this encoding to the message payload. If blank it uses the original encoding. This property accepts values defined by the ruby Encoding class (https://ruby-doc.org/core-2.3.0/Encoding.html). Ex: UTF_8, ASCII_8BIT, etc.
delivery	:batch	The delivery mode for the consumer. Possible values: :message, :batch, :inline_batch. See Phobos documentation for more details.
session_timeout	300	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	10	Interval between offset commits, in seconds.
offset_commit_threshold	0	Number of messages that can be processed before their offsets are committed. If zero, offset commits are not triggered by message processing
heartbeat_interval	10	Interval between heartbeats; must be less than the session window.
backoff	(1000..60_000)	Range representing the minimum and maximum number of milliseconds to back off after a consumer error.

Defining Database Pollers

These are used when polling the database via rake deimos:db_poller. You can create a number of pollers, one per topic.

Deimos.configure do
  db_poller do
    producer_class 'MyProducer'
    run_every 2.minutes
  end
end

Config name	Default	Description
producer_class	nil	ActiveRecordProducer class to use for sending messages.
run_every	60	Amount of time in seconds to wait between runs.
timestamp_column	:updated_at	Name of the column to query. Remember to add an index to this column!
delay_time	2	Amount of time in seconds to wait before picking up records, to allow for transactions to finish.
full_table	false	If set to true, do a full table dump to Kafka each run. Good for very small tables.
start_from_beginning	true	If false, start from the current time instead of the beginning of time if this is the first time running the poller.

Kafka Configuration

Config name	Default	Description
kafka.logger	Deimos.config.logger	Logger passed to RubyKafka.
kafka.seed_brokers	['localhost:9092']	URL for the Kafka brokers.
kafka.client_id	phobos	Identifier for this application.
kafka.connect_timeout	15	The socket timeout for connecting to the broker, in seconds.
kafka.socket_timeout	15	The socket timeout for reading and writing to the broker, in seconds.
kafka.ssl.enabled	false	Whether SSL is enabled on the brokers.
kafka.ssl.ca_cert	nil	A PEM encoded CA cert, a file path to the cert, or an Array of certs to use with an SSL connection.
kafka.ssl.client_cert	nil	A PEM encoded client cert to use with an SSL connection, or a file path to the cert.
kafka.ssl.client_cert_key	nil	A PEM encoded client cert key to use with an SSL connection.

Consumer Configuration

These are top-level configuration settings, but they can be overridden by individual consumers.

Config name	Default	Description
consumers.session_timeout	300	Number of seconds after which, if a client hasn't contacted the Kafka cluster, it will be kicked out of the group.
consumers.offset_commit_interval	10	Interval between offset commits, in seconds.
consumers.offset_commit_threshold	0	Number of messages that can be processed before their offsets are committed. If zero, offset commits are not triggered by message processing
consumers.heartbeat_interval	10	Interval between heartbeats; must be less than the session window.
consumers.backoff	(1000..60_000)	Range representing the minimum and maximum number of milliseconds to back off after a consumer error.
consumers.reraise_errors	false	Default behavior is to swallow uncaught exceptions and log to the metrics provider. Set this to true to instead raise all errors. Note that raising an error will ensure that the message cannot be processed - if there is a bad message which will always raise that error, your consumer will not be able to proceed past it and will be stuck forever until you fix your code. See also the fatal_error configuration. This is automatically set to true when using the TestHelpers module in RSpec.
consumers.report_lag	false	Whether to send the consumer_lag metric. This requires an extra thread per consumer.
consumers.fatal_error	proc { false }	Block taking an exception, payload and metadata and returning true if this should be considered a fatal error and false otherwise. E.g. you can use this to always fail if the database is available. Not needed if reraise_errors is set to true.

Producer Configuration

Config name	Default	Description
producers.ack_timeout	5	Number of seconds a broker can wait for replicas to acknowledge a write before responding with a timeout.
producers.required_acks	1	Number of replicas that must acknowledge a write, or :all if all in-sync replicas must acknowledge.
producers.max_retries	2	Number of retries that should be attempted before giving up sending messages to the cluster. Does not include the original attempt.
producers.retry_backoff	1	Number of seconds to wait between retries.
producers.max_buffer_size	10_000	Number of messages allowed in the buffer before new writes will raise BufferOverflow exceptions.
producers.max_buffer_bytesize	10_000_000	Maximum size of the buffer in bytes. Attempting to produce messages when the buffer reaches this size will result in BufferOverflow being raised.
producers.compression_codec	nil	Name of the compression codec to use, or nil if no compression should be performed. Valid codecs: :snappy and :gzip
producers.compression_threshold	1	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.
producers.max_queue_size	10_000	Maximum number of messages allowed in the queue. Only used for async_producer.
producers.delivery_threshold	0	If greater than zero, the number of buffered messages that will automatically trigger a delivery. Only used for async_producer.
producers.delivery_interval	0	if greater than zero, the number of seconds between automatic message deliveries. Only used for async_producer.
producers.persistent_connections	false	Set this to true to keep the producer connection between publish calls. This can speed up subsequent messages by around 30%, but it does mean that you need to manually call sync_producer_shutdown before exiting, similar to async_producer_shutdown.
producers.schema_namespace	nil	Default namespace for all producers. Can remain nil. Individual producers can override.
producers.topic_prefix	nil	Add a prefix to all topic names. This can be useful if you're using the same Kafka broker for different environments that are producing the same topics.
producers.disabled	false	Disable all actual message producing. Generally more useful to use the disable_producers method instead.
producers.backend	:kafka_async	Currently can be set to :db, :kafka, or :kafka_async. If using Kafka directly, a good pattern is to set to async in your user-facing app, and sync in your consumers or delayed workers.

Schema Configuration

Config name	Default	Description
schema.backend	:mock	Backend representing the schema encoder/decoder. You can see a full list here.
schema.registry_url	http://localhost:8081	URL of the Confluent schema registry.
schema.path	nil	Local path to find your schemas.

Database Producer Configuration

Config name	Default	Description
db_producer.logger	Deimos.config.logger	Logger to use inside the DB producer.
db_producer.log_topics	[]	List of topics to print full messages for, or :all to print all topics. This can introduce slowdown since it needs to decode each message using the schema registry.
db_producer.compact_topics	[]	List of topics to compact before sending, i.e. only send the last message with any given key in a batch. This is an optimization which mirrors what Kafka itself will do with compaction turned on but only within a single batch. You can also specify :all to compact all topics.

Configuration Syntax

Sample:

Deimos.configure do
  logger Logger.new(STDOUT)
  # Nested config field
  kafka.seed_brokers ['my.kafka.broker:9092']

  # Multiple nested config fields via block
  consumers do
    session_timeout 30
    offset_commit_interval 10
  end

  # Define a new producer
  producer do
    class_name 'MyProducer'
    topic 'MyTopic'
    schema 'MyTopicSchema'
    key_config field: :id
  end

  # Define another new producer
  producer do
    class_name 'AnotherProducer'
    topic 'AnotherTopic'
    schema 'AnotherSchema'
    key_config plain: true
  end

  # Define a consumer
  consumer do
    class_name 'MyConsumer'
    topic 'TopicToConsume'
    schema 'ConsumerSchema'
    key_config plain: true
    # include Phobos / RubyKafka configs
    start_from_beginning true
    heartbeat_interval 10 
  end

end

Note that all blocks are evaluated in the context of the configuration object. If you're calling this inside another class or method, you'll need to save things you need to reference into local variables before calling configure.