2181
Apache ZooKeeper distributed coordination service
Apache ZooKeeper
What is port 2181?
Port 2181 is used by Apache ZooKeeper, a distributed coordination service for large-scale distributed systems including Kafka, HBase, and Hadoop. It manages configuration data, naming, distributed synchronization, and group membership. An exposed ZooKeeper instance can leak sensitive cluster configuration and potentially allow an attacker to disrupt or take control of the entire distributed system.
Quick checks
$
nc -zv example.com 2181
$
nmap -p 2181 example.com
$
telnet example.com 2181