This project contains a Docker image meant to facilitate the deployment of Apache ZooKeeper on Kubernetes using StatefulSets.
Scaling is not currently supported. An ensemble’s membership cannot be updated in a safe way in ZooKeeper 3.4.10 (The current stable release).
Observers are currently not supported. Contributions are welcome.
Persistent Volumes must be used. emptyDirs will likely result in a loss of data.
The docker image contained in this repository is comprised of a base Ubuntu 16.04 image using the latest release of the OpenJDK JRE based on the 1.8 JVM (JDK 8u111) and the latest stable release of ZooKeeper, 3.4.10. Ubuntu is a much larger image than BusyBox or Alpine, but these images contain mucl or ulibc. This requires a custom version of OpenJDK to be built against a libc runtime other than glibc. No vendor of the ZooKeeper software supplies or verifies the software against such a JVM, and, while Alpine or BusyBox would provide smaller images, we have prioritized a well-known environment.
The image is built such that the ZooKeeper process is designated to run as a non-root user. By default, this user is zookeeper. The ZooKeeper package is installed into the /opt/zookeeper directory, all configuration is symlinked into the /usr/etc/zookeeper/, and all executables are symlinked into /usr/bin. The ZooKeeper data directories are contained in /var/lib/zookeeper. This is identical to the RPM distribution that users should be familiar with.
The Log Level configuration may be modified via the ZK_LOG_LEVEL environment variable as described above. However, the location of the log output is not modifiable. The ZooKeeper process must be run in the foreground, and the log information will be shipped to the stdout. This is considered to be a best practice for containerized applications, and it allows users to make use of the log rotation and retention infrastructure that already exists for K8s.
The zkMetrics script can be used to retrieve metrics from the ZooKeeper process and print them to stdout. A recurring Kubernetes job can be used to collect these metrics and provide them to a collector.
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