Brent Segner and Ryan O’Donnell explain how clustering works with Apache NiFi:
Although it is entirely possible to deploy NiFi in a single node configuration, this does not represent a best practice for an enterprise graded deployment and would introduce unnecessary risk into a production environment where scaling to meet demand and resiliency are paramount. In order to get around this concern, as of release 1.0.0, NiFi provides the ability to cluster nodes together using either an embedded or external Apache Zookeeper instance as a highly reliable distributed coordinator. While a simple Google search shows there is plenty of debate around whether it is better to use an embedded or external Zookeeper service as both sides have merit, for the sake of argument and this blog, we will use the embedded flavor in the deployment.
Click through for more information, including a walkthrough on configuration.