---
title: "Comment by Hayrullah Kar on \"Event-Driven Fundamentals: Why PulseCart Moved Off Request-Response\" | Hashnode"
description: "This is a phenomenal architectural write-up! Moving from tightly coupled orchestration to event-driven choreography is the exact inflection point where an e-com"
url: "https://hashnode.com/posts/event-driven-fundamentals-why-pulsecart-moved-off-request-response/6a361b93b730bb04633adf30/comment/6a38639dbf6b850c285ff834"
---

[Discussion](https://hashnode.com/posts/event-driven-fundamentals-why-pulsecart-moved-off-request-response/6a361b93b730bb04633adf30)

Comment [Event-Driven Fundamentals: Why PulseCart Moved Off Request-Response](https://hashnode.com/posts/event-driven-fundamentals-why-pulsecart-moved-off-request-response/6a361b93b730bb04633adf30)

[Hayrullah Kar](https://hashnode.com/@magesheet)

[Jun 21](https://hashnode.com/posts/event-driven-fundamentals-why-pulsecart-moved-off-request-response/6a361b93b730bb04633adf30/comment/6a38639dbf6b850c285ff834)

This is a phenomenal architectural write-up! Moving from tightly coupled orchestration to event-driven choreography is the exact inflection point where an e-commerce platform transitions from an MVP to a resilient, enterprise-grade system.

Your breakdown of the event taxonomy—specifically the distinction between an immutable fact (order.placed) and an orchestration command masquerading as an event—is a crucial lesson that many backend engineers learn the hard way. Validating the envelope contract via Pydantic before it ever touches the message broker is a beautiful pattern that keeps the pipeline loud and reliable.

If I can offer one supportive critique for the upcoming Day 2 topic: when you dive into Google Cloud Pub/Sub subscriptions, it would be awesome to see how you handle idempotency on the consumer side, especially since Pub/Sub guarantees at-least-once delivery.

Looking forward to the deep dive into dead-letter topics! Outstanding work!

[Madhav Bhasin](https://hashnode.com/@madhavbhasin)

[Jun 22](https://hashnode.com/posts/event-driven-fundamentals-why-pulsecart-moved-off-request-response/6a361b93b730bb04633adf30/comment/6a38639dbf6b850c285ff834#reply-6a396cdebf60a8e532dab634)

Thanks, glad it resonated! You're right that idempotency is exactly where Pub/Sub's at-least-once delivery bites people, so it's front and center in Day 2. I'm planning to cover deduplication keys on the consumer (carrying a stable event ID through the envelope and tracking processed IDs) alongside the dead-letter topic setup. Curious whether you've leaned more on broker-side dedup or handled it in the application layer — always interested in what's held up in production.