Is system In Pain

Learn system design the painful way — the way that sticks. Build real systems, run traffic through them, and watch them break.

Deterministic simulator — same architecture, same result, every time. No signup.

↘ flip the scenario

SIM · TINYURL-1PASSING

traffic

100 req/min

p99

142ms

avail

99.9%

score

DATABASE OVERLOADCACHE MISS STORMQUEUE BACKLOGAPI TIMEOUTRATE LIMIT REACHEDREGIONAL OUTAGESERVER CRASHNETWORK LATENCY SPIKEREPLICATION LAGCONNECTION POOL EXHAUSTEDDATABASE OVERLOADCACHE MISS STORMQUEUE BACKLOGAPI TIMEOUTRATE LIMIT REACHEDREGIONAL OUTAGESERVER CRASHNETWORK LATENCY SPIKEREPLICATION LAGCONNECTION POOL EXHAUSTED

Learning through cause & effect.

THE LOOP →

Build

Drag components onto the canvas and wire a real architecture.

Simulate

Run live traffic through a deterministic engine — packets and all.

Observe

Watch nodes saturate, queues back up, bottlenecks turn red.

Optimize

Scored on latency, cost, resilience. Never on checkboxes.

One server → planet scale.

Foundations

TinyURL · Pastebin · Write Firehose

Surviving Traffic

Flash Sale · Lean Startup · Event Pipeline

Scaling Reads & Writes

Global Reads · Viral Scale · Read Replica

Resilience & Security

Always On · Bot Flood · Overwhelmed

Break your first system.

Five levels. A deterministic engine. Zero diagrams to memorize.

systemInPain.com — the Duolingo of system design