Home > Communication Service Provider Solutions > Telecom Multicloud Foundation > Canonical > Guides > Reference Architecture—Canonical Charmed OpenStack (Ussuri) on Dell EMC Hardware > How MAAS works
MAAS has a tiered architecture with a central Postgres database backing a region controller regiond that deals with operator requests. Distributed rack controllers, or rackd, provide high-bandwidth services to multiple racks. The controller itself is stateless and horizontally scalable and only presents a REST API.
Rackd provides DHCP, PXE, TFTP, and other local services. They cache large items like operating system install images at the rack level for performance but maintain no exclusive state other than credentials to talk to the region controller.