SystemDesignCosmos Distributed Systems & Scale
High-Scale Distributed Systems Architecture Visualizer

Master System Design & Scale.

Interactive visualizers for Consistent Hashing rings, Raft consensus leader elections, distributed Token/Leaky bucket rate limiters, CAP Theorem network partitions, Circuit Breakers, Kafka partition rebalances, Write-Ahead Log (WAL) crash recovery, and back-of-the-envelope capacity estimations.

Explore 20 Concepts Capacity Calculator
Distributed Partitioning Engine

Consistent Hashing Ring & Virtual Nodes

Hash Ring Range: [0x00000000 ➔ 0xFFFFFFFF] (0° ➔ 360°)4 Active Nodes
Server A
Ring Position: 45°
Server B
Ring Position: 135°
Server C
Ring Position: 225°
Server D
Ring Position: 315°
Clockwise Key Routing Map:
user_849 (70°)➔ Server B
session_91 (190°)➔ Server C
cart_102 (340°)➔ Server A
Ring Event Log:

Consistent Hash Ring initialized with 4 physical servers.

Distributed Consensus Engine

Raft Leader Election & Quorum Replicated Log

QUORUM HEALTHY (5/5 Nodes Alive)
Current Term Epoch: 1Quorum Threshold: 3 of 5 Votes
Node 1
Leader
Term: 1
Log Entries: 2
Node 2
Follower
Term: 1
Log Entries: 2
Node 3
Follower
Term: 1
Log Entries: 2
Node 4
Follower
Term: 1
Log Entries: 2
Node 5
Follower
Term: 1
Log Entries: 2
Consensus Event Log:

Raft 5-node cluster running smoothly in Term 1. Node 1 is Leader.

API Gateway Traffic Shaping

Distributed Rate Limiter Simulator

TOKEN-BUCKET ALGORITHM
Current Gateway Capacity Utilization:8 / 10 Tokens Available
Traffic Gateway Log:

Rate Limiter running. Token bucket has 8/10 tokens available.

Distributed Systems Tradeoffs

CAP Theorem & Network Partition Explorer

Node 1 (US Data Center):
Balance: $100
Status: Accepting Writes
Node 2 (EU Data Center):
Balance: $100
Fails Writes (Preserves Strict Consistency)
Resilience & Fault Tolerance

Circuit Breaker & Cascading Failure Prevention Stepper

STATE: CLOSED
1. CLOSED (Normal)

All traffic passes through. Failures counted: 0/5

2. OPEN (Fast-Fail)

100% traffic rejected immediately. DB given breathing room.

3. HALF-OPEN (Canary)

Sends 1 trial probe request to test backend recovery.

Circuit Event Log:

Circuit Breaker is CLOSED (Normal healthy operation). Traffic flowing to downstream DB.

Distributed Event Streaming

Kafka Partition Log & Consumer Group Rebalance

Topic: orders-stream (3 Partitions)
Partition #0Offset: 2
Append-Only Commit Log:
Order #101[0]
Order #104[1]
Assigned: Consumer A
Partition #1Offset: 2
Append-Only Commit Log:
Order #102[0]
Order #105[1]
Assigned: Consumer B
Partition #2Offset: 2
Append-Only Commit Log:
Order #103[0]
Order #106[1]
Assigned: Consumer C
Kafka Broker Event Log:

Kafka Topic "orders-stream" running with 3 partitions and 3 consumers.

Database Storage Engine & Durability

Write-Ahead Log (WAL) & Crash Recovery Stepper

ACID DURABILITY PROTECTED
Volatile In-Memory Buffer (RAM):Live
Balance: $100

Volatile memory subject to power failure loss.

Persistent Write-Ahead Log (NVMe):fsync() committed
TX#101: init balance=100
Execution Trace:

Database running normally. Ready to execute transaction.

Horizontal Database Partitioning

Database Sharding & Range-Key Routing Engine

Target: Shard 3
Test User Shard Key Routing (e.g. Email):
Shard #1Users A - H
Shard 1 (DB Cluster US-East)
Existing Records:
alice@corp.io
charlie@dev.net
bob@test.com
Shard #2Users I - P
Shard 2 (DB Cluster US-West)
Existing Records:
jack@scale.com
lisa@cloud.org
mike@ops.io
Shard #3Users Q - Z
Shard 3 (DB Cluster EU-Central)
Existing Records:
rachel@arch.net
sam@db.io
zack@data.ai
Distributed Cache Strategy

Cache-Aside vs Write-Through vs Write-Behind

CACHE-ASIDE
Execution Flow Diagram:
1. Client Application
2. Redis / Memcached
3. PostgreSQL Database
Staff Architect Estimation Engine

Back-of-the-Envelope Capacity & Scale Calculator

Scale: 50M DAU
Daily Active Users (DAU):50 Million
Reads / User / Day:40 Reads
Writes / User / Day:4 Writes
Item Payload Size:2 KB
Peak Read QPS (2.5x):
57,870 QPS

Avg: 23,148 QPS

Peak Write QPS (2.5x):
5,788 QPS

Avg: 2,315 QPS

Yearly Storage:
135.8 TB / Year

+381 GB / Day

80/20 RAM Cache Size:
763 GB RAM

20% of daily read data

20 In-Depth Lessons

Write-Ahead Logs, Circuit Breakers, Bulkheads, Kafka consumer partitions, XFetch early expiration, and PACELC.

Raft Consensus Lab

Kill leaders, simulate heartbeats, trigger candidate elections, and verify quorum log replication.

Staff Flashcards

Master tough FAANG Staff Architect interview questions on quorum math, XFetch proofs, and WAL crash recovery.