Internet-Security.com TCP port 2888 details

Apache ZooKeeper uses TCP port 2888 as the quorum peer port for follower-to-leader communication using its Zab (ZooKeeper Atomic Broadcast) protocol.
In standard configurations (zoo.cfg), entries like server.1=zk1:2888:3888 designate 2888 for peer replication traffic and 3888 for leader election.
Because ZooKeeper underpins many systems, deployments of Apache Kafka (pre-KRaft mode), Apache Hadoop/HDFS NameNode HA, Apache HBase, Apache SolrCloud, and Apache Storm typically have their ZooKeeper nodes listening on 2888 for intra-cluster communication.
Vendor/managed distributions such as Cloudera and Hortonworks/Ambari also run ZooKeeper with 2888 as the default peer port unless reconfigured.

TCP 2888