High Availability Routing for Postgres (HARP) v2.0
HARP 2.0 is a complete rewrite of HARP 1.0 and is currently in Beta status. It should not be used in any Production, Pre-Production, User Acceptance Testing, or other critical environment. It is supplied in its current form as-is for testing purposes only. While not likely, features, functionality, syntax, or other aspects may be changed without warning in future releases to facilitate a production-quality release.
High Availability Routing for Postgres (HARP) is a cluster management tool for Bi-directional Replication (BDR) clusters. The core design of the tool is to route all application traffic within a single data center or region to only one node at a time. This node, designated the Lead Master, acts as the principle write target to reduce the potential for data conflicts.
HARP leverages a distributed consensus model to determine availability of the BDR nodes in the cluster. On failure or unavailability of the Lead Master, HARP elects a new Lead Master and redirects application traffic accordingly.
Together with the core capabilities of BDR, this mechanism of routing application traffic to the Lead Master node enables fast failover and switchover without risk of data loss.
HARP requires BDR versions 3.6 and above.