Automated Failover and High Availability in Postgress

Here's how this problem is solved in a professional PostgreSQL setup:

Automated Failover and High Availability (HA)

To handle a night-time failure, businesses use a specialized piece of software called a High Availability (HA) Manager or Cluster Manager. This software constantly watches the Primary and Standby databases and automatically executes the recovery steps if the Primary fails.

1. The Watchdog: The HA Manager

The HA Manager (popular examples include Patroni, repmgr, or Corosync/Pacemaker) acts as a "watchdog."

• Continuous Monitoring: It constantly checks the Primary database to see if it's responding.
• Failure Detection: If the Primary doesn't respond for a short, predetermined amount of time (e.g., 30 seconds), the manager declares it dead.
• Automatic Promotion: The manager automatically selects the most up-to-date Standby database and executes the promotion command (pg_ctl promote). The Standby immediately becomes the new Primary.

2. DNS/Connection Rerouting

Once the promotion is complete, the application needs to know where the new Primary is.

• The HA Manager updates a configuration setting (often a DNS record or a Virtual IP) to point the application traffic to the newly promoted server.
• The application starts sending all its write traffic to the new Primary.
• The system is now restored, and the old, failed Primary is left offline.

Key Benefits of Automation

This automated approach ensures the system recovers quickly without any human intervention: