Node types v5
Data nodes
A data node in PGD is a node which runs a Postgres instance. It replicates data to all other data nodes. It also participates in the cluster wide Raft decision making around locking and leadership. It will be the member of one or more groups and by default will be a member of the "top level" group which spans all data nodes in the cluster.
Witness nodes
A witness node behaves like a data node in that it participates in the cluster wide Raft decision making around locking and leadership. It does not replicate or store data though. The purpose of a witness node is to be available to ensure a majority can be achieved when the cluster seeks a consensus. The Witness nodes section has more details.
Logical standby nodes
Logical standby nodes are nodes which recieve the logical data changes from another node and replicate them locally. They can be used to replace the node they are replicating, if that node should become unavailable, with some caveats. See Logical standby nodes for more details.
Physical standby nodes
Physical standby nodes are nodes which recieve the physical data changes from another node writing them locally. They can be used to replace the node they are recieving the changes from. See Physical standby nodes for further details.
Subscriber-only nodes
A subscriber-only node is a data node which, as the name suggests, only subscribes to changes in the cluster but does not replicate changes to other nodes. Subscriber-only nodes can be used as read-only nodes for applications. Subscriber-only nodes are created by taking a data node and adding it to a subscriber-only group. See Subscriber-only nodes and groups for more details.