fundamentals

The junior-filter question that still separates candidates who understand the model from those who memorised a definition. The answer is three mechanical differences and one economic one.

Roles versus users looks like syntax trivia and is actually a secrets-management position. The follow-ups about instance profiles and IRSA separate practitioners from tutorial graduates.

The right answer depends on who owns the truth: the platform, the caller, or nobody. At scale there is a fourth option most candidates miss, where your image pipeline publishes values instead of Terraform hunting for them.

The default answer is 'horizontal' because interviews reward it. The correct answer names the constraint that makes distribution expensive and knows when one big machine is the engineering choice.