PostgreSQL 12 High Availability Cookbook - Third Edition

Why HAProxy?

Part of improving our stack is to understand its weaknesses. Even our repmgr design called for the use of a virtual IP address. The primary complication here is that a virtual IP can be declared from anywhere and, if not properly managed, can lead to a split-brain scenario.

HAProxy doesn't have that limitation because every IP address acts as if it were the primary node. So, as long as we connect through the proxy port we choose during configuration, we're communicating with whichever node is the primary at that specific moment. HAProxy acts as a routing layer, rather than a single floating resource.