PostgreSQL 12 High Availability Cookbook - Third Edition

Why Patroni?

Patroni is the glue that binds these pieces together. It acts as a master coordinator and serves a number of roles. This is the process it uses on every PostgreSQL server:

1. It checks for the presence of an existing primary server in the Raft layer.
2. If no primary server is found, it inserts a key in the Raft layer claiming the primary role.
3. If this server is the primary, it signals the HAProxy layer to use it as the new redirection target.
4. If a primary server is found, it performs several checks and attempts to transform the current server into a replica.

Patroni repeats these steps every few seconds on every server where it is installed. As a consequence, some outages may result in race conditions where multiple replicas will ...