Delta Reporting and CFEngine are not centralized applications. Yes, I do describe DR as centralized reporting for CFEngine, but that is a simplistic view for easy consumption. Both CFEngine and Delta Reporting are far more flexible.
A typical installation of CFEngine has all agent hosts connecting to a single CFEngine server, but did you know that you can do more? In a DMZ you can deploy a DMZ mirror CFEngine server to act as a proxy between the DMZ host agents and the internal CFEngine server. The mirror is a server for DMZ agents and is itself an agent of the internal server. In isolated networks you can deploy additional CFEngine servers to support local agent hosts.
Delta Reporting's promise outcome and class log can be similarly distributed. Each CFEngine server loads DR's data to a database that can be local or remote. Multiple CFEngine servers can share the same DR database, and you can have isolated DR instances in high security networks.
It is no exaggeration that CFEngine is decentralized and scales enormously, and Delta Reporting was designed the same way.