Looking for pointers about replication internal working

[Han]

Hi,

I'm reading an old annotated version of the Cassandra paper (
https://docs.datastax.com/en/articles/cassandra/cassandrathenandnow.html)
,  and am curious about this annotation about "Replication" section:

Zookeeper usage was restricted to Facebook’s in-house Cassandra branch;
Apache Cassandra has always avoided it.

<snip>

Is there any paper or blog or other pointers to understand what Apache
Cassandra did to avoid Zookeeper?

Thanks!

Han