Apache ZooKeeper is an open source solution for managing synchronization of distributed applications. It provides monitoring and leader election services for ThingWorx nodes. At least three ZooKeeper nodes are recommended in a HA configuration. The number of ZooKeeper instances needs to be an odd number to maintain a quorum, with more instances providing higher availability.

The Connection Servers, ThingWorx Foundation, and Ignite all use ZooKeeper for service discovery. Service discovery is the ability for one application to automatically find instances of another application and react to changes in the available servers.

ThingWorx Foundation uses ZooKeeper for coordination across the ThingWorx nodes. It is used for singleton selection, which is basically the coordination of schedules and timers across the nodes so that no task is run more than once. It is also used for functional coordination to ensure a behavior is controlled across the cluster.

Prior to installing Zookeeper, read and understand all installation documents including documentation for any necessary prerequisite software such as Java. It is important to understand and apply proper settings, including security recommendations. When installing Java for ZooKeeper, PTC recommends disabling client-initiated renegotiation (or jdk.tls.rejectClientInitiatedRenegotiation=true).

You can download ZooKeeper from http://zookeeper.apache.org/releases.html. For version compatibility information, see the PTC Release Advisor.

You can find guidelines for deploying ZooKeeper in its Administration Guide at https://zookeeper.apache.org under Documentation, which includes supported platforms and required software. For ThingWorx HA, a clustered (multi-server) setup of ZooKeeper should be deployed. Apache refers to a ZooKeeper cluster as an ensemble.

Client port 2181 must be open between this server and Ignite, the Connection Server, and ThingWorx Foundation. The other ports listed below are required between the individual ZooKeeper nodes.