@type callback() ::
  (members :: [member_id()], partitions :: [partition()] ->
     %{required(member_id()) => [partition()]})

A function that can assign partitions.

members is a list of member IDs and partitions is a list of partitions that need to be assigned to a group member.

The return value must be a map with member IDs as keys and a list of partition assignments as values. For each member ID in the returned map, the assigned partitions will become the assignments argument to KafkaEx.GenConsumer.Supervisor.start_link/4 in the corresponding member process. Any member that's omitted from the return value will not be assigned any partitions.

example

Example

Given the following members and partitions to be assigned:

members = ["member1", "member2", "member3"]
partitions = [{"topic", 0}, {"topic", 1}, {"topic", 2}]

One possible assignment is as follows:

ExampleGenConsumer.assign_partitions(members, partitions)
#=> %{"member1" => [{"topic", 0}, {"topic", 2}], "member2" => [{"topic", 1}]}

In this case, the consumer group process for "member1" will launch two KafkaEx.GenConsumer processes (one for each of its assigned partitions), "member2" will launch one KafkaEx.GenConsumer process, and "member3" will launch no processes.

@type member_id() :: binary()

The ID (string) of a member of a consumer group, assigned by a Kafka broker.

@type partition() :: {topic(), partition_id()}

A partition of a single topic (embeds the name of the topic).

@type partition_id() :: integer()

The integer ID of a partition of a Kafka topic.

@type topic() :: binary()

The string name of a Kafka topic.