The following describes NSP cluster redundancy rules:
At each site, a master is elected among the cluster of three VMs. In a DR deployment, the cluster in one site is designated as the primary, meaning it is the preferred active cluster. The site is referred to as the primary site. The second cluster and site are referred to as secondary and therefore act as the standby backup cluster or site.
The application processes at the standby site are shut down, but the neo4j and other databases are synchronized with the primary active site.
Switching to the secondary standby site can be initiated manually or by using an automated approach stemming from the loss of heartbeat between the primary and standby sites.
When the NSP cluster at the primary active site is down (two out of three servers must be inactive, shut down, or failed), the heartbeat mechanism between the primary and standby NSP clusters fails after three timeouts. This initiates the active role at the secondary standby site.
When the NSP cluster at the primary site is back up, the heartbeat mechanism between the primary/standby and secondary/active NSP clusters is restored. The primary site can be restored to the active role manually. Automatic reversion to the primary NSP cluster is not supported.