Apache ZooKeeper

Apache ZooKeeper 3.9, env-var driven like every container in this collection: the entrypoint renders zoo.cfg from typed variables, supervises the server with ezx, and exposes the shared composite health endpoint. Use it when you need ZooKeeper itself (legacy Kafka, other coordinators); Kafka 3.9+ images here run KRaft and do not need it.

Quickstart

bash

docker run -d \
  --name zookeeper \
  -v zookeeper-data:/opt/containers/data \
  -p 2181:2181 \
  ghcr.io/supanadit/containers/apache-zookeeper

Verify from another container:

bash

echo ruok | nc zookeeper 2181   # imok
curl -s http://localhost:8080/health

Configuration

Variable	Default	Description
`ZOOKEEPER_CLIENT_PORT`	`2181`	Client-facing port.
`ZOOKEEPER_TICK_TIME`	`2000`	Base tick unit in ms; heartbeats and timeouts are multiples of it.
`ZOOKEEPER_MAX_CLIENT_CNXNS`	`60`	Max concurrent connections per client IP.
`ZOOKEEPER_ADMIN_ENABLE_SERVER`	`false`	Enables the Jetty admin server (`ZOOKEEPER_ADMIN_SERVER_PORT`).
`ZOOKEEPER_ADMIN_SERVER_PORT`	`8081`	Admin server port — moved off 8080, which belongs to the ezx health API.
`ZOOKEEPER_DATA_DIR`	`/opt/containers/data`	Data dir; the transaction log lives in its `log/` subdirectory.
`ZOOKEEPER_CONFIG_DIR`	`/opt/containers/config`	Where `zoo.cfg` is generated (also honours `ZOOCFGDIR`).
`ZOOKEEPER_LOG_DIR`	`/opt/containers/logs`	Rotated application logs.
`ZOOKEEPER_USER` / `ZOOKEEPER_GROUP`	`zookeeper`	Account the server drops to.
`SLEEP_MODE`	`false`	Start the supervisor but not the server (debugging).

The container owns the data and log directories; ZooKeeper's own ZOO_* tuning knobs stay in zoo.cfg and are rendered from the variables above.

Health

The health check probes TCP on the client port, so /health reports healthy as soon as ZooKeeper accepts client connections. The ezx API listens on port 8080:

bash

curl -s http://localhost:8080/health

See Health & readiness for the full endpoint contract.

Ensemble (clustering)

A three-node ensemble is the smallest fault-tolerant configuration. The container has no dedicated clustering variables: ZooKeeper ensembles are declared with standard server.N lines, so append them by mounting a drop-in fragment alongside the generated config in /opt/containers/config:

yaml

services:
  zk-1:
    image: ghcr.io/supanadit/containers/apache-zookeeper
    volumes:
      - zk-1-data:/opt/containers/data
      - ./zk-1.cfg:/opt/containers/config/zoo.cfg.d/server.cfg:ro

Next steps

Configuration — how env vars become config files.
Volumes — the /opt/containers/* layout.
Apache Kafka — runs KRaft, no ZooKeeper required.