1. zeneventserver
In Zenoss 3.1.1 the event processing was managed by zenhub daemon because of that there was bottleneck in event processing which has caused some performance related issues, so to avoid that in Zenoss 4.x they have introduced new daemon zeneventserver.
zeneventserver daemon which is written in java, interact with Rabbitmq and fetch the events from zenevents queue[zenoss.queues.zep.zenevents]and insert into the events tables that are in zenoss_zep database where the events are getting stored.
Another responsibility of this daemon is to fetch the event related information like [resource, summary, last seen, first seen, severity etc.], in Java Script Object Notation [JSON] format so that it get displayed in zenoss UI also moves the event to zenoss zenoss.queues.zep.signal queue. Zenpack installation is taken care by this daemon. [Event Class creation while installing zenpack]