The Agent would be a standalone service that acts as a sort of mirror to mdns. It would receive AXFR/IXFR, NOTIFYs, and other notifications and perform changes to a DNS server through a plugin-style backend. The agent is intended for deployments that may not be able to use mdns as a true DNS Master.
HTTP REST API service for Designate
Software service running on a central management node that stores information persistently in a backend storage using a configurable driver like SQLAlchemy or other.
Also known as mini dns. This is a dns server with limited capabilities like NOTIFY’s, AXFR’s and record queries. The pool manager uses mdns to transfer data to/from the pool servers.
A message queue, typically something like RabbitMQ or ZeroMQ
name server
A FQDN (or IP, but usually a FQDN) that is used to populate the NS Records of a Designate Managed Zone. Each Pool will have a set of Name Servers, which users then delegate to from their registrar.
A server, physical or virtual, running some aspect of the designate system.
A collection of pool servers sharing similar attributes. Different pools could have different capabilities - such as GeoIP / Round Robin DNS / Anycast.
pool manager
This is a service that is responsible for notifying pool servers of the changes that have occurred. It also updates central once the changes are live on the pool servers.
pool manager backend
A backend is used by the pool manager to transfer the data from storage to name servers. There are backends that support PowerDNS, BIND, & NSD.
pool server
The DNS servers that are updated by the pool manager. These need not be the same as the name servers. When they are different a mechanism outside of designate is needed to ensure the data on pool servers is consistent with that on the name servers.
private pool

A pool of ‘private’ DNS servers. These servers would typically allow non standard TLDs (.dev , .local etc), and may not have the same level of blacklist restrictions. They would be aimed at people with Neutron Networking, and VPC style set ups, where access to the DNS server would come from trusted networks (E.G. in-cloud - owned instances, and onsite resources connect by VPN)

This would allow customers to set DNS entries for internal servers, on domains that would not be available on the public pools, and have them accessible by internal users

secondary zone
A zone within Designate that has external Masters.
Optional Software Service that is configured to listen to events from the Nova or Neutron event queue and use the central service to generate simple A records for instances as they are created, and delete A records as they are deleted.
A backend for storing data/information persistently. Typically MongoDB or a SQL based server software.