Class: Karafka::Routing::Topic

Inherits:
Object
  • Object
show all
Defined in:
lib/karafka/routing/topic.rb

Overview

Note:

‘#group` is the polymorphic reference to the owning group. Today this is always a ConsumerGroup, but the accessor is named generically in preparation for additional group types (e.g. KIP-932 share groups). `#consumer_group` is kept as an alias for backwards compatibility.

Topic stores all the details on how we should interact with Kafka given topic. It belongs to a group as from 0.6 all the topics can work in the same group It is a part of Karafka’s DSL.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(name, group) ⇒ Topic

Returns a new instance of Topic.

Parameters:

  • name (String, Symbol) —

    name of a topic on which we want to listen

  • group (Karafka::Routing::ConsumerGroup) —

    owning group of this topic. Polymorphic placeholder for future group types (e.g. share groups); today always a ConsumerGroup.



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# File 'lib/karafka/routing/topic.rb', line 45

def initialize(name, group)
  @name = name.to_s
  @group = group
  @attributes = {}
  @active = true
  # @note We use identifier related to the group that owns a topic, because from Karafka 0.6
  #   we can handle multiple Kafka instances with the same process and we can have same
  #   topic name across multiple groups
  @id = "#{group.id}_#{@name}"
  @consumer = nil
  @active_assigned = false
  @subscription_group_details = nil

  INHERITABLE_ATTRIBUTES.each do |attribute|
    instance_variable_set("@#{attribute}", nil)
  end
end

Instance Attribute Details

#consumer ⇒ Class

Returns consumer class that we should use.

Returns:

  • (Class) —

    consumer class that we should use



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# File 'lib/karafka/routing/topic.rb', line 96

def consumer
  if consumer_persistence
    # When persistence of consumers is on, no need to reload them
    @consumer
  else
    # In order to support code reload without having to change the topic api, we re-fetch the
    # class of a consumer based on its class name. This will support all the cases where the
    # consumer class is defined with a name. It won't support code reload for anonymous
    # consumer classes, but this is an edge case
    begin
      Object.const_get(@consumer.to_s)
    rescue NameError
      # It will only fail if the in case of anonymous classes
      @consumer
    end
  end
end

#group ⇒ Object (readonly) Also known as: consumer_group

Returns the value of attribute group.



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# File 'lib/karafka/routing/topic.rb', line 14

def group
  @group
end

#id ⇒ Object (readonly)

Returns the value of attribute id.



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# File 'lib/karafka/routing/topic.rb', line 14

def id
  @id
end

#name ⇒ Object (readonly)

Returns the value of attribute name.



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# File 'lib/karafka/routing/topic.rb', line 14

def name
  @name
end

#subscription_group ⇒ Object

Full subscription group reference can be built only when we have knowledge about the whole routing tree, this is why it is going to be set later on



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# File 'lib/karafka/routing/topic.rb', line 26

def subscription_group
  @subscription_group
end

#subscription_group_details ⇒ Object

Returns the value of attribute subscription_group_details.



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# File 'lib/karafka/routing/topic.rb', line 22

def subscription_group_details
  @subscription_group_details
end

Instance Method Details

#active(active) ⇒ Object

Allows to disable topic by invoking this method and setting it to ‘false`.

Parameters:

  • active (Boolean) —

    should this topic be consumed or not



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# File 'lib/karafka/routing/topic.rb', line 116

def active(active)
  # Do not allow for active overrides. Basically if this is set on the topic level, defaults
  # will not overwrite it and this is desired. Otherwise because of the fact that this is
  # not a full feature config but just a flag, default value would always overwrite the
  # per-topic config since defaults application happens after the topic config block
  unless @active_assigned
    @active = active
    @active_assigned = true
  end

  @active
end

#active? ⇒ Boolean

Returns should this topic be in use.

Returns:

  • (Boolean) —

    should this topic be in use



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# File 'lib/karafka/routing/topic.rb', line 139

def active?
  # Never active if disabled via routing
  return false unless @active

  Karafka::App.config.internal.routing.activity_manager.active?(:topics, name)
end

#consumer_class ⇒ Class

Note:

This is just an alias to the ‘#consumer` method. We however want to use it internally instead of referencing the `#consumer`. We use this to indicate that this method returns class and not an instance. In the routing we want to keep the `#consumer Consumer` routing syntax, but for references outside, we should use this one.

Returns consumer class that we should use.

Returns:

  • (Class) —

    consumer class that we should use



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# File 'lib/karafka/routing/topic.rb', line 134

def consumer_class
  consumer
end

#kafka=(settings = {}) ⇒ Object

Note:

It is set to ‘false` by default to preserve backwards compatibility

Often users want to have the same basic cluster setup with small setting alterations This method allows us to do so by setting ‘inherit` to `true`. Whe inherit is enabled, settings will be merged with defaults.

Parameters:

  • settings (Hash) (defaults to: {}) —

    kafka scope settings. If ‘:inherit` key is provided, it will instruct the assignment to merge with root level defaults



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# File 'lib/karafka/routing/topic.rb', line 84

def kafka=(settings = {})
  inherit = settings.delete(:inherit)

  @kafka = inherit ? Karafka::App.config.kafka.merge(settings) : settings
end

#subscription_name ⇒ String

Returns name of subscription that will go to librdkafka.

Returns:

  • (String) —

    name of subscription that will go to librdkafka



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# File 'lib/karafka/routing/topic.rb', line 91

def subscription_name
  name
end

#to_h ⇒ Hash

Note:

This is being used when we validate the group and its topics

Returns hash with all the topic attributes.

Returns:

  • (Hash) —

    hash with all the topic attributes



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# File 'lib/karafka/routing/topic.rb', line 148

def to_h
  map = INHERITABLE_ATTRIBUTES.map do |attribute|
    [attribute, public_send(attribute)]
  end

  map.to_h.merge!(
    id: id,
    name: name,
    active: active?,
    consumer: consumer,
    group_id: group.id,
    # Kept as a reference alongside `group_id` for backwards compatibility. Will be removed
    # in Karafka 3.0.
    consumer_group_id: group.id,
    subscription_group_details: subscription_group_details
  ).freeze
end