What is a Cluster?

Most of all, cluster is a compatibility unit. It is set of modules that is developed by the same group of people, build and release at once.

Most of the reasoning that lead to creation of the concept can be found at our Installation Structure document.

What is the relation between a module and a cluster?

A module and a NB cluster are two incompatible terms. They are allowed to have various relations (1:1, 1:N, N:1, N:N), depending on source code organization in a module and installation structure in the final product (clusters). Module cluster may, but must not match a module. One cluster can be constructed from unlimited number of modules. Two clusters (in theory) can be constructed from different sub-trees of the same modules. One module (in theory) can host unlimited number of clusters.