ZooKeeper

Apache Druid supports ZooKeeper versions 3.5.x and above.

The operations that happen over ZK are

1. Segment “publishing” protocol from Historical
2. Segment load/drop protocol between and Historical
3. and MiddleManager task management

The and are used for this.

All processes publish themselves on the , specifically, they will create an ephemeral znode at

Which signifies that they exist. They will also subsequently create a permanent znode at

Processes like the Coordinator and can then watch these paths to see which processes are currently serving which segments.

The is used for this.

When the decides that a Historical process should load or drop a segment, it writes an ephemeral znode to