A transactional application relies on a single Postgres database. If the database goes down — planned maintenance or hardware failure — the entire application is unavailable. Add a standby replica that can take over automatically.
A failover replica is a synchronized copy of the database that automatically promotes to primary when the original goes down, removing the database as a single point of failure. The benefit is high availability with an RTO of seconds to a few minutes instead of hours — most cloud providers automate the promotion, making database downtime a rare and brief event. Use it when database unavailability has critical business impact; accept that the replica may carry a small replication lag and that transactions not yet flushed on the primary at the moment of failure may be lost.
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