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# 3.3.7 Cluster Formation

A cluster is represented by a group of servers that have a common leader. A cluster is a virtual non-existent (empty) node that describes a group of a server as one whole.

* Forming a cluster is only possible within the conditions specified by the topology (a node that joins the network receives a “license” to open its cluster
* Each cluster has a leader who collects data based on voting results. After a given number of rounds (also determined by the topology processor), a change of leader occurs. This leads to the change of all permalinks – those inside the cluster, and those leading inside it and outside as well.
* The change of permalinks is one of the transactions of the topological processor and is written inside the ledger.
* A cluster can have a limit on its width (number of nodes inside it) and depth (the number of other clusters connected to it by permalinks)
* In case of loss of connection on the existing permalinks, the remounting operation is provided. It performs the regrouping of nodes in the absence of communication with the “parent cluster.”