PRTG Manual: Install a Cluster
PRTG offers one single failover cluster in all licenses, including the Freeware Edition. A single failover cluster consists of two machines (master node and failover node) that each run one installation of PRTG. They are connected to each other and exchange configuration and monitoring data. You can run a cluster with up to five cluster nodes.
This feature is not available in PRTG Hosted Monitor.
For more information, see section Failover Cluster Configuration.
What is the clustering feature in PRTG?