README.md 8.4 KB
Supported tags and respective Dockerfile links
For more information about this image and its history, please see the relevant manifest file (library/zookeeper). This image is updated via pull requests to the docker-library/official-images GitHub repo.
For detailed information about the virtual/transfer sizes and individual layers of each of the above supported tags, please see the repos/zookeeper/tag-details.md file in the docker-library/repo-info GitHub repo.
What is Apache Zookeeper?
Apache ZooKeeper is a software project of the Apache Software Foundation, providing an open source distributed configuration service, synchronization service, and naming registry for large distributed systems. ZooKeeper was a sub-project of Hadoop but is now a top-level project in its own right.
How to use this image
Start a Zookeeper server instance
$ docker run --name some-zookeeper --restart always -d zookeeper
This image includes EXPOSE 2181 2888 3888 (the zookeeper client port, follower port, election port respectively), so standard container linking will make it automatically available to the linked containers. Since the Zookeeper "fails fast" it's better to always restart it.
Connect to Zookeeper from an application in another Docker container
$ docker run --name some-app --link some-zookeeper:zookeeper -d application-that-uses-zookeeper
Connect to Zookeeper from the Zookeeper command line client
$ docker run -it --rm --link some-zookeeper:zookeeper zookeeper zkCli.sh -server zookeeper
... via docker-compose
Example docker-compose.yml for zookeeper:
version: '2'
services:
zoo1:
image: zookeeper
restart: always
ports:
- 2181:2181
environment:
ZOO_MY_ID: 1
ZOO_SERVERS: server.1=zoo1:2888:3888 server.2=zoo2:2888:3888 server.3=zoo3:2888:3888
zoo2:
image: zookeeper
restart: always
ports:
- 2182:2181
environment:
ZOO_MY_ID: 2
ZOO_SERVERS: server.1=zoo1:2888:3888 server.2=zoo2:2888:3888 server.3=zoo3:2888:3888
zoo3:
image: zookeeper
restart: always
ports:
- 2183:2181
environment:
ZOO_MY_ID: 3
ZOO_SERVERS: server.1=zoo1:2888:3888 server.2=zoo2:2888:3888 server.3=zoo3:2888:3888
This will start Zookeeper in replicated mode. Run docker-compose up and wait for it to initialize completely. Ports 2181-2183 will be exposed.
Please be aware that setting up multiple servers on a single machine will not create any redundancy. If something were to happen which caused the machine to die, all of the zookeeper servers would be offline. Full redundancy requires that each server have its own machine. It must be a completely separate physical server. Multiple virtual machines on the same physical host are still vulnerable to the complete failure of that host.
Consider using Docker Swarm when running Zookeeper in replicated mode.
Configuration
Zookeeper configuration is located in /conf. One way to change it is mounting your config file as a volume:
$ docker run --name some-zookeeper --restart always -d -v $(pwd)/zoo.cfg:/conf/zoo.cfg zookeeper
Environment variables
ZooKeeper recommended defaults are used if zoo.cfg file is not provided. They can be overridden using the following environment variables.
$ docker run -e "ZOO_INIT_LIMIT=10" --name some-zookeeper --restart always -d 31z4/zookeeper
ZOO_TICK_TIME
Defaults to 2000. ZooKeeper's tickTime
The length of a single tick, which is the basic time unit used by ZooKeeper, as measured in milliseconds. It is used to regulate heartbeats, and timeouts. For example, the minimum session timeout will be two ticks
ZOO_INIT_LIMIT
Defaults to 5. ZooKeeper's initLimit
Amount of time, in ticks (see tickTime), to allow followers to connect and sync to a leader. Increased this value as needed, if the amount of data managed by ZooKeeper is large.
ZOO_SYNC_LIMIT
Defaults to 2. ZooKeeper's syncLimit
Amount of time, in ticks (see tickTime), to allow followers to sync with ZooKeeper. If followers fall too far behind a leader, they will be dropped.
Replicated mode
Environment variables below are mandatory if you want to run Zookeeper in replicated mode.
ZOO_MY_ID
The id must be unique within the ensemble and should have a value between 1 and 255. Do note that this variable will not have any effect if you start the container with a /data directory that already contains the myid file.
ZOO_SERVERS
This variable allows you to specify a list of machines of the Zookeeper ensemble. Each entry has the form of server.id=host:port:port. Entries are separated with space. Do note that this variable will not have any effect if you start the container with a /conf directory that already contains the zoo.cfg file.
Where to store data
This image is configured with volumes at /data and /datalog to hold the Zookeeper in-memory database snapshots and the transaction log of updates to the database, respectively.
Be careful where you put the transaction log. A dedicated transaction log device is key to consistent good performance. Putting the log on a busy device will adversely affect performance.
License
View license information for the software contained in this image.
Supported Docker versions
This image is officially supported on Docker version 17.03.1-ce.
Support for older versions (down to 1.6) is provided on a best-effort basis.
Please see the Docker installation documentation for details on how to upgrade your Docker daemon.
User Feedback
Issues
If you have any problems with or questions about this image, please contact us through a GitHub issue. If the issue is related to a CVE, please check for a cve-tracker issue on the official-images repository first.
You can also reach many of the official image maintainers via the #docker-library IRC channel on Freenode.
Contributing
You are invited to contribute new features, fixes, or updates, large or small; we are always thrilled to receive pull requests, and do our best to process them as fast as we can.
Before you start to code, we recommend discussing your plans through a GitHub issue, especially for more ambitious contributions. This gives other contributors a chance to point you in the right direction, give you feedback on your design, and help you find out if someone else is working on the same thing.
Documentation
Documentation for this image is stored in the zookeeper/ directory of the docker-library/docs GitHub repo. Be sure to familiarize yourself with the repository's README.md file before attempting a pull request.