ZooKeeper is commonly used as a distributed key-value store. A lot of systems use it for storing configuration, doing service discovery, or for doing distributed locking.
This page aims to document the network protocol used by Zookeeper clients to talk to Zookeeper nodes.
Ports
| Service | Protocol | Port |
|---|---|---|
| Zookeeper | TCP | 2181 |
| ClickHouse Keeper | TCP | 9181 |
Protocol notes
When the client connects, it learns a session ID, which seems to be incremented by 1 for each new connection. So the server must be keeping track of the last session ID it gave out.
Integers are big-endian.
Message types
| Opcode | Name | Description |
|---|---|---|
| N/A | Handshake | To establish a connection |
| 1 | Create | Create a node |
Handshake
On connecting to a Zookeeper node, the client sends a handshake request packet. In return, the server responds with a handshake response packet.
These handshake packets are slightly different from all the other packets in that they do not contain the xid and packet type fields.
Client -> Server
| Length | Name | Description |
|---|---|---|
| 4 | Length | Length of the remaining packet |
| 4 | Protocol version | Protocol version number, always 0 |
| 4 | Last seen zxid | Last seen zxid |
blah blah blah
Server -> Client
blah blah blah
Some useful resources
- https://clickhouse.com/codebrowser/ClickHouse/src/Common/ZooKeeper/ZooKeeperConstants.h.html
- https://clickhouse.com/codebrowser/ClickHouse/src/Common/ZooKeeper/ZooKeeperCommon.cpp.html#277
- https://zookeeper.apache.org/doc/r3.9.1/zookeeperProgrammers.html
- https://zookeeper.apache.org/doc/r3.9.1/recipes.html