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.

Once a ThingWorx node gains leadership, it maintains a session with ZooKeeper and maintains the leadership position. If the session expires because the ThingWorx node fails to respond, the ZooKeeper service selects a ThingWorx standby node to be the next leader. The ThingWorx node is notified that it is now the leader and it takes the leadership position, fully connects to the database, and starts handling traffic.

ZooKeeper nodes also monitor each other’s status. If the active node fails, then a new ZooKeeper leader is elected. This provides high availability for the ZooKeeper service through an internal mechanism for these nodes. The ThingWorx servers are configured with the addresses of all ZooKeeper nodes, which enables them to find the current ZooKeeper leader.

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 (i.e. jdk.tls.rejectClientIntiatedRenegotiation=true).

ZooKeeper can be downloaded from: http://zookeeper.apache.org/releases.html.

Guidelines for deploying ZooKeeper are provided here, including supported platforms and required software: http://zookeeper.apache.org/doc/r3.4.5/zookeeperAdmin.html#ch_deployment

For ThingWorx HA, a clustered (multi-server) setup of ZooKeeper should be deployed. Apache refers a ZooKeeper cluster as an ensemble. Guidance for establishing a ZooKeeper ensemble is provided here: http://zookeeper.apache.org/doc/r3.4.5/zookeeperAdmin.html#sc_zkMulitServerSetup

With ZooKeeper up and running, ThingWorx HA can be activated. The following process configures ThingWorx to recognize and work with the ZooKeeper servers. One of the steps in this process is only necessary when one ZooKeeper ensemble is supporting multiple ThingWorx HA configurations.

At this point, all ThingWorx servers should be operating and can accessed. However, only one ThingWorx server should have access to the database and its content.