---
title: "Comment by Mateo Ruiz on \"How I built and scaled real‑time chat app from 2 to millions of users — without a rewrite?\" | Hashnode"
description: "One thing I really liked here is that the architecture optimizes for failure scenarios, not just happy-path throughput. The transactional outbox + CDC pattern s"
url: "https://hashnode.com/posts/how-i-built-and-scaled-real-time-chat-app-from-2-to-millions-of-users-without-a-rewrite/6a43c12fa4907beae8c291ed/comment/6a46467815814c6cc3f57a5b"
---

[Discussion](https://hashnode.com/posts/how-i-built-and-scaled-real-time-chat-app-from-2-to-millions-of-users-without-a-rewrite/6a43c12fa4907beae8c291ed)

Comment [How I built and scaled real‑time chat app from 2 to millions of users — without a rewrite?](https://hashnode.com/posts/how-i-built-and-scaled-real-time-chat-app-from-2-to-millions-of-users-without-a-rewrite/6a43c12fa4907beae8c291ed)

[Mateo Ruiz](https://hashnode.com/@mateoruiz)

[Jul 2](https://hashnode.com/posts/how-i-built-and-scaled-real-time-chat-app-from-2-to-millions-of-users-without-a-rewrite/6a43c12fa4907beae8c291ed/comment/6a46467815814c6cc3f57a5b)

One thing I really liked here is that the architecture optimizes for failure scenarios, not just happy-path throughput. The transactional outbox + CDC pattern solves the reliability problem first, and the scalability benefits naturally follow.

Another takeaway is your point about keeping the app tier stateless by pushing fanout downstream. That's a design choice that pays off long before you hit "millions of users" because deployments, scaling, and operations all become simpler.

Also appreciated the discussion around HTML-over-the-wire. Whether someone agrees with that choice or not, it's refreshing to see the trade-offs explained instead of treating any architecture as universally correct.

Great write-up that focuses on engineering decisions rather than just technology choices.

[Nguyen Engineer](https://hashnode.com/@finnng)

[Jul 6](https://hashnode.com/posts/how-i-built-and-scaled-real-time-chat-app-from-2-to-millions-of-users-without-a-rewrite/6a43c12fa4907beae8c291ed/comment/6a46467815814c6cc3f57a5b#reply-6a4b84a67e8d4647eccf4748)

Thank you. Let me know if you find any part worth extending for more detail.