Introduction to pg_auto_failover¶
pg_auto_failover is an extension for PostgreSQL that monitors and manages failover for a postgres clusters. It is optimised for simplicity and correctness.
pg_auto_failover implements Business Continuity for your PostgreSQL services. pg_auto_failover implements a single PostgreSQL service using multiple nodes with automated failover, and automates PostgreSQL maintenance operations in a way that guarantees availability of the service to its users and applications.
To that end, pg_auto_failover uses three nodes (machines, servers) per PostgreSQL service:
- a PostgreSQL primary node,
- a PostgreSQL secondary node, using Synchronous Hot Standby,
- a pg_auto_failover Monitor node that acts both as a witness and an orchestrator.
The pg_auto_failover Monitor implements a state machine and relies on in-core PostgreSQL facilities to deliver HA. For example. when the secondary node is detected to be unavailable, or when its lag is reported above a defined threshold (the default is 1 WAL files, or 16MB, see the pgautofailover.promote_wal_log_threshold GUC on the pg_auto_failover monitor), then the Monitor removes it from the synchronous_standby_names setting on the primary node. Until the secondary is back to being monitored healthy, failover and switchover operations are not allowed, preventing data loss.