System Design Cheat Sheet: 1-Page Architecture Guide
Latency Numbers, Back-of-the-Envelope Math, and 4-Step Architecture Framework
The 4-Step System Design Interview Framework 1-Page Cheatsheet
Step 1: Scoping & Requirements (5-7 min)
When to use: Never start drawing right away
Clarify 3 core functional requirements and 3 non-functional requirements (Availability 99.99%, latency < 100ms, read/write QPS).
Step 2: Capacity Estimation (5 min)
When to use: Round numbers for mental math
DAU -> QPS -> Storage per day (QPS * size * 86,400) -> 5-year storage -> Memory for 80/20 cache rule.
Step 3: High-Level Architecture (10-15 min)
When to use: Client -> CDN -> Gateway -> Services
Draw load balancer, application stateless servers, database (Primary/Replica), cache layer, and asynchronous worker queues.
Step 4: Deep Dive & Bottlenecks (15 min)
When to use: Scale from single server to distributed
Address Single Point of Failure (SPOF), DB sharding keys, cache invalidation, replication lag, and rate limiting.
Database & Storage Selection Matrix 1-Page Cheatsheet
Relational (PostgreSQL / MySQL)
When to use: ACID transactions, financial ledger, complex JOINs
Scale with read replicas, connection pooling (PgBouncer), and sharding by customer_id.
NoSQL Key-Value (DynamoDB / Redis)
When to use: Fast O(1) lookups by primary key, user session store
Partition key distributes data across shards automatically. Low operational overhead.
Columnar / Search (Elasticsearch / ClickHouse)
When to use: Full-text search, analytical logs, aggregations
Inverted index for substring queries; columnar compression for high-throughput scans.