---
title: "Dayul Lee (@dayul) | Hashnode"
description: "Management informs. Engineering decides.\nCode is strategy. Every architecture decision has a reason. Read the latest articles by Dayul Lee on Hashnode."
url: "https://hashnode.com/@dayul"
---

@dayul

# Dayul Lee

@dayul · Seoul, South Korea · Joined May 2026

Management informs. Engineering decides. Code is strategy. Every architecture decision has a reason.

### [Network Part 5 - CDN, WebSocket, and Idempotency: When the Parts Meet Traffic](https://lukyday.hashnode.dev/network-part-5-cdn-websocket-and-idempotency-when-the-parts-meet-traffic?utm_source=hashnode&utm_medium=feed)

Four real scenarios — image loading, real-time chat, global routing, and payment retries — where Parts 1–4 stop being theory and start being architecture decisions.

14 min read · [lukyday.hashnode.dev](https://lukyday.hashnode.dev/network-part-5-cdn-websocket-and-idempotency-when-the-parts-meet-traffic?utm_source=hashnode&utm_medium=feed)

[May 13](https://hashnode.com/posts/network-part-5-cdn-websocket-and-idempotency-when-the-parts-meet-traffic/6a04bc19a0c1540277626a29)

### [Network Part 4 - The Load Balancer as an Information Choice](https://lukyday.hashnode.dev/network-part-4-the-load-balancer-as-an-information-choice?utm_source=hashnode&utm_medium=feed)

From the limits of DNS round-robin to the trade-offs of L4/L7 load balancers — where you split traffic determines what your system can and cannot do.

10 min read · [lukyday.hashnode.dev](https://lukyday.hashnode.dev/network-part-4-the-load-balancer-as-an-information-choice?utm_source=hashnode&utm_medium=feed)

[May 12](https://hashnode.com/posts/network-part-4-the-load-balancer-as-an-information-choice/6a0333ec937b84f7798aed18)

### [Network Part 3 - How HTTP Outgrew TCP](https://lukyday.hashnode.dev/network-part-3-how-http-outgrew-tcp?utm_source=hashnode&utm_medium=feed)

From HOL Blocking to QUIC — how HTTP/1.1, HTTP/2, and HTTP/3 each made a different call on what to keep and what to let go, read through Path Dependency and the Innovator's Dilemma.

8 min read · [lukyday.hashnode.dev](https://lukyday.hashnode.dev/network-part-3-how-http-outgrew-tcp?utm_source=hashnode&utm_medium=feed)

[May 11](https://hashnode.com/posts/network-part-3-how-http-outgrew-tcp/6a01df77fca21b0d4b2b3732)

### [Network Part 2 - The Cost of a TCP Handshake](https://lukyday.hashnode.dev/network-part-2-the-cost-of-a-tcp-handshake?utm_source=hashnode&utm_medium=feed)

The structural cost of TCP's 3-way handshake — what RTT and TIME\_WAIT mean under high-volume traffic, and why Transaction Cost Theory explains the birth of Keep-Alive.

5 min read · [lukyday.hashnode.dev](https://lukyday.hashnode.dev/network-part-2-the-cost-of-a-tcp-handshake?utm_source=hashnode&utm_medium=feed)

[May 8](https://hashnode.com/posts/network-part-2-the-cost-of-a-tcp-handshake/69fde56d3c7289793162a940)

### [Network Part 1 - The OSI Model as a Fault Map](https://lukyday.hashnode.dev/network-part-1-the-osi-model-as-a-fault-map?utm_source=hashnode&utm_medium=feed)

How to read the OSI model as a bottleneck diagnostic tool — the distinct failure modes of L4 and L7, and why Conway's Law explains the layered design.

5 min read · [lukyday.hashnode.dev](https://lukyday.hashnode.dev/network-part-1-the-osi-model-as-a-fault-map?utm_source=hashnode&utm_medium=feed)

[May 7](https://hashnode.com/posts/network-part-1-the-osi-model-as-a-fault-map/69fc905b5133a7775e5f204c)