Operations
Every instance has a pool of 20 database connections. What is wrong with that plan?
Whether the candidate reasons about a shared, finite resource across the whole fleet rather than per instance.
The situation behind the question
A service runs 8 instances with a pool of 20. It scales to 40 instances under load. The Postgres instance allows 500 connections; a reporting tool holds 60, and a migration job needs 5. During the next spike, the migration cannot connect and the deploy fails halfway through.