Assigning leaders is trivial with something like zookeeper. But in this case it appears that the leader metadata is stored in a table of the database itself, which raises questions of operability if those tablets are unavailable.
YDB doesn't use Zookeeper. The system is built of tablets, every tablet implements distributed consensus algorithm. There are different types of tablets in the system, say SchemeShard is tablet that stores metadata, table schema for instance. DataShard stores table partition data.
