|Traditionally, the expression cluster refers to a single instance of Postgres managing multiple databases; an EDB Ark database server cluster is a collection of high-availability Postgres server instances that reside in a cloud or on a traditional network.
When you create a new cluster (a group of replicated database servers),
EDB Ark initializes one or more Postgres instances (virtual machines) according to your specifications.
EDB Ark uses Postgres streaming replication to synchronize replicas in the cluster, and pgpool-II to implement load balancing and connection pooling among all active instances. Figure 2.1 provides a general overview of the EDB Ark architecture.
EDB Ark installs Postgres on each replica node in a read-only hot-standby role that automatically duplicates all data found on the master node, and all changes made to that data. In hot-standby mode, the data is available to service user queries providing read scalability to the cluster (see Figure 2.2)
. In addition, any schema changes made to the master are also replicated to the replica nodes, making development and deployment of application changes easy and seamless without interruption to normal operations.
EDB Ark automatically archives data at regular intervals; you can specify a convenient backup window and how many backups to retain when creating a database cluster.
EDB Ark also offers backup on demand - simply click the Backup icon to save a copy of the instance. Automatic backups are retained according to your specifications; on-demand backups are retained until you delete them. Each backup is a complete copy of the cluster; you can use a backup to restore a cluster.
EDB Ark makes it easy to scale a database cluster: