ZooKeeper

ZooKeeper is a centralized service for maintaining configuration information, naming, and providing distributed synchronization for large-scale clusters.

Distributed systems fail when coordination breaks: ZooKeeper prevents this by acting as a high-availability source of truth. It manages critical tasks like leader election (via ephemeral nodes), configuration management, and group membership for heavyweights like Hadoop, Kafka, and HBase. By using a hierarchical namespace similar to a file system (znodes) and the Zab consensus protocol, it ensures strict order and data consistency across thousands of nodes. It is the industry standard for turning chaotic distributed fleets into synchronized, reliable infrastructure.

https://zookeeper.apache.org/