Masters
Clients
Admin
NeoCTL
Storages
DB
DB
As NEO is distributed, different types of nodes are involved:
One of master nodes gets elected to become the "primary master node", other becoming "secondary master nodes". The primary handles all centralised tasks, such as OID/TID generation, cluster consistency checking and broadcasting cluster changes to all nodes. When a primary master falls, secondaries take over by restarting an election.
Storages nodes are responsible of load and store operations requested by client nodes. It contains replication facilities so they can mirror other storage nodes' cells. They embed a relational database that act as a key/value backend with transactional facilities.
Client nodes implements the Storage API and talk with the primary master and storage nodes on demand. Those nodes are multithreaded to fit with requirements of the ZODB API.
The admin node is the standard way to interact with NEO internals, it is for example required at bootstrap to decide which partition table should be used or collect statistical data.
NeoCTL is a command line utility to access admin node and control the cluster.