Level Up Coding System Design Newsletter

How Discord Fans Out One Message to a Million Users

A case study in fanout, bottlenecks, and the engineering decisions behind Discord's scale.

32 mins ago • Nikki Siapno

1

June 2026

LLMs: The Essential Guide

Most engineers only see the API layer. Here's what's happening underneath.

Jun 26 • Nikki Siapno

33

4

MCP Clearly Explained

Plus: Big upgrades are coming to LUC. Vote on what you'd like to see first.

Jun 15 • Nikki Siapno

44

3

5

May 2026

REST vs GraphQL vs gRPC

The tradeoffs behind resource-driven, query-driven, and method-driven APIs.

May 28 • Nikki Siapno

35

7

Service Discovery in Distributed Systems Clearly Explained

How modern systems dynamically locate healthy services as infrastructure constantly changes.

May 13 • Nikki Siapno

17

2

Docker vs Kubernetes

(4 min read) | The real difference that actually matters, how to decide, where teams go wrong, and more...

May 11 • Nikki Siapno

35

2

2

OAuth Clearly Explained

(4 min read) | OAuth flow, three different tokens, three different jobs, what OAuth actually solves, where OAuth systems usually break, and more

May 1 • Nikki Siapno

99

1

11

April 2026

Infrastructure as Code Clearly Explained

The IaC workflow that actually works, why it matters in practice, security risks you can't ignore, and more...

Apr 27 • Nikki Siapno

18

3

Redis Clearly Explained

How Redis works under the hood, where it fits in the stack, where it shines, and when NOT to use it.

Apr 21 • Nikki Siapno

84

3

10

Database Indexing Clearly Explained

(4 minutes) | What indexes really do, index types, how the optimizer decides, when they help (and when they hurt), and the right mental model

Apr 13 • Nikki Siapno

46

1

7

Circuit Breakers: How to Stop Small Failures from Spreading

(4 Minutes) | What they are, what triggers a trip, why they help so much, observability, and when to use them (and when not to)

Apr 9 • Nikki Siapno

20

3

March 2026

REST APIs Properly Explained

(4 minutes) | Constraints, trade-offs, when not to use it, and more

Mar 31 • Nikki Siapno

66

2

8