At a previous company, we hit a point where our PostgreSQL database was clearly becoming a bottleneck. The primary instance was responsible for every user-facing search request, including some heavy queries from long-time users with years of historical data. CPU usage kept climbing, and before long, we were already running on the largest instance size available. Vertical scaling had officially hit its limit.

Naturally, the next step was to introduce read replicas. On paper, it sounded straightforward. In reality, it wasn’t.