What are invariants in system design?

Invariants are rules that must always hold true for your business logic — like a payment always linking to an order. Ignore them, invite bugs.

How do you find the transactional center?

Ask: Where's the authority for core state

Absolutely. Interviewers love candidates who prioritize logic over tools. Sketch invariants, then planes. Stand out.

🗄️ Databases & Backend

We've all chased shiny tools like Kafka before nailing the logic. Big mistake. Start with invariants for systems that actually work.

theAIcatchup Apr 08, 2026 4 min read

Start with invariants, not infrastructure — it's the foundation of reliable systems. 𝕏
Use the transactional center (e.g., Postgres) for core state to avoid distributed bugs. 𝕏
Scale reactively with the Four Plane Model: core, reactions, analytics, history. 𝕏

Published by

Ship faster. Build smarter.

#distributed systems #invariants #system design interview #system-design #transactional center

Get the best Developer Tools stories of the week in your inbox — no noise, no spam.

Originally reported by dev.to