Animated diagram: an OTP login and payment system. Requests flow from the app through a gateway to auth, OTP, sessions and the ledger. A traffic spike breaks the SMS provider until a queue is added, and a retry storm double-charges a payment until an idempotency key is added.
Design the system. Then watch it break.
System-design interview questions from a working solutions architect. Banking, login and identity, drawn from the naive version to the one that survives real traffic. Plus AI for Builders: real AI builds, with the design, the evals and the cost.
Interview questions, answered like the real system
The core series. Each video takes one question you could be asked in a system-design round, builds the naive answer first, breaks it under real traffic, and fixes it one component at a time.
The diagram at the top of this page is two of these: the OTP spike and the double charge.
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Design OTP login that survives 70M users
The naive SMS-OTP table, and the festival-night spike that melts it.
Login and identity
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How does UPI stay up on festival sale days?
The naive single-switch picture, and where a bank's side times out.
Banking and payments
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Design payment retries that never charge twice
The naive retry loop, and the idempotency keys that fix it.
Banking and payments
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Design passkey login for a bank
What changes in login design, and the recovery path that breaks it.
Login and identity
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Design session handling when one user logs in on two devices
The naive single token, and the logout that never lands.
Login and identity
AI for Builders
The second series. Each video starts from something that was actually built with AI, then shows how it works, where it breaks and what it costs. Fewer hot takes, more evidence.
- Architecture teardowns
- How a real AI system fits together, and the one trade-off that matters.
- Build logs
- A build with AI agents, from the design to the evals to the bill in rupees.
- India in context
- What an AI shift means for Indian companies, with local prices and numbers.
Made by a working architect
Architect Radio is one person: a software and solutions architect with a full-time job in the field. The questions are the ones architects really get asked to answer, and the examples stay anonymous: never a real company's internals.
Every script starts from real sources. The narration is in my own voice and the illustrations are drawn with AI, disclosed on every video. New videos every week, with Shorts in between.
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