System Design Classroom

Never Let the Model Choose the tenant_id

Tenant isolation was hard before AI. Agents, RAG, and AI-written code just made the blast radius bigger.

Oct 31 • Raul Junco

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Good Saga Design Starts with the Order of the Steps

Warning: this article might make you reopen a saga you already shipped.

Oct 22 • Raul Junco

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September 2026

AI Agents Just Rediscovered the Dual-Write Problem

The distributed-systems failure hiding between agent state and the real world.

Sep 26 • Raul Junco

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The Most Dangerous Agent Memory Was Once Correct

How outdated facts, changing policies, and stale indexes create confident but incorrect decisions.

Sep 12 • Raul Junco

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August 2026

Your AI Agent Won’t Crash. It Will Happily Pay an Invoice Without Approval

A practical guide to observing AI decisions with OpenTelemetry

Aug 22 • Raul Junco

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July 2026

Safe Database Rollback Starts Before Deployment

How to deploy schema changes without painting yourself into a corner.

Jul 25 • Raul Junco

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How to Survive the Recommendation Engine Question

Most engineers focus on the matching algorithm. The real test is separating generation from serving.

Jul 11 • Raul Junco

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June 2026

A Good System Design Tackles Down the Hot Path First

Before you add cache, replicas, queues, or microservices, understand where the system actually feels pressure.

Jun 13 • Raul Junco

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May 2026

Most System Design Mistakes Hide Between the Boxes

Five gaps your architecture diagrams don't show

May 30 • Raul Junco

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Bad Retries Can Break Good Systems

A practical guide to using backoff, jitter, retry budgets, idempotency, and circuit breakers in backend systems.

May 9 • Raul Junco

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April 2026

Event-Driven Systems Are Easy to Build but Hard to Keep Correct

4 ways event-driven systems fail without looking broken

Apr 25 • Raul Junco

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Consistency is negotiable. But the bill always lands somewhere.

Linearizable, causal, eventual, and quorum: how to pick the right consistency guarantee for each workflow in your system.

Apr 18 • Raul Junco

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