Apache Druid (incubating) uses Apache ZooKeeper (ZK) for management of current cluster state. The operations that happen over ZK are
We use the Curator LeadershipLatch recipe to do leader election at path
servedSegmentsPath are used for this.
Which signifies that they exist. They will also subsequently create a permanent znode at
And as they load up segments, they will attach ephemeral znodes that look like
loadQueuePath is used for this.
This znode will contain a payload that indicates to the Historical process what it should do with the given segment. When the Historical process is done with the work, it will delete the znode in order to signify to the Coordinator that it is complete.