3.Internals

ZooKeeper's leader-based atomic broadcast protocol, proposal ordering, quorum acknowledgment, recovery, and its distinction from Paxos/Raft.

Watch notifications, one-shot/re-registration semantics, ordering, disconnect gaps, and cache reconciliation.

The hierarchical znode namespace and why it resembles a filesystem while serving coordination metadata rather than files.

Persistent, ephemeral, sequential nodes; versions; ACLs; session ownership; and coordination semantics.

Majority-quorum availability, leader failover, ensemble sizing, and why more servers do not always increase fault tolerance.