how client know the server's topology

[yonghua]

Hello,

I am seeing this doc:
https://github.com/zendesk/ruby-kafka  who says:
----
This behavior is controlled by the required_acks option to #producer and 
#async_producer:

# This is the default: all replicas must acknowledge.
producer = kafka.producer(required_acks: :all)
----


My question is that, how the client knows the server's topology?
including the replicas locations and number it must know for accepting 
all acknowledges.

Thanks.