The client part implements ZODB.Storage API, allowing NEO to be used as a drop-in replacement in any application using the Zope Object DataBase, including low-level client-side data caching. It uses the Multi-Queue caching algorythm, which improves memory usage efficiency when used as a 2nd-level cache as is the case with ZODB.
A master node is a process providing functions of sequential number generation (OIDs and TIDs), transaction control including object cache invalidation notifications for clients, and storage nodes load-balancing decisions. Due to its function, it is important for good performance for master node to be quickly reachable from any other node, limiting the distance between them.
A storage node is a process providing persistent storage space. This storage is used for database objects and associated transaction meta-data, and also contains NEO meta-data: current partition table and number generators state.
An admin node is a process listening for notifications from a master node and archiving them to provide administrator with cluster health monitoring. It also serves as an administrative command relay.
Neoctl is a comman-line tool to allow querying cluster state and issuing commands, such as adding or dropping a storage from cluster.
It is important to note that object data never goes through any node but storage and client.