PostgreSQL Primary-Secondary Cluster with asynchronous replication.

Three member replica sets provide enough redundancy to survive most network partitions and other system failures. These sets also have sufficient capacity for many distributed read operations. Replica sets should always have an odd number of members. This ensures that elections will proceed smoothly. For more about designing replica sets, see the Replication overview.
More info at http://www.mongodb.org/

A set of MySQL/MariaDB cluster topologies for automatic installation and further discovery of new database nodes based on the pre-configured schemas.