/System-Design-Cheatsheet

System Design Cheatsheet

  1. Functional Requirements
  2. Non-Functional Requirements
  3. High-Level Architecture
  4. Deep-Dive into a single Service

Functional Requirements

  • Be comprehensive - Create full list of features and discuss what to include in the focus
  • If there are multiple data types, describe them all
  • Always add:
    • Monitoring / Resilience
    • Usage Analytics
    • Payment flow
    • Authentication
    • Full-Text Search / filtering by category
  • Reduce: e.g. don't describe the CDN functionality if it is not the scope
  • Are we talking CRUD - Create Remove Update Delete?

Non-Functional Requirements

Assumptions

  • CAP theorem: Prioritize Availability vs. Consistency
  • Read heavy (10,000/1) vs. write heavy (50/1)
    • Get a specific number
      • Number of users /Daily active users
      • Number of Writes = Reads * x
    • Purchase rate: 1/1000
    • Requests/Queries per seconds "qpr"
    • How big is one entry
    • Multiple data types with different sizes?
  • Availability:
    • Reduncancy
  • Response time: If < 50ms, we need geo-location
    • Where are users located?
  • Storage: If unlimited, plan for 3 years of storage
    • A day has 100,000 seconds
    • 3 years have 1000 days = 100,000,000 seconds
  • Throughput
    • 1 GBit per second = 100 Megabyte per second
  • Hotspots (Time vs. DB entry)
    • Assume 1000x than average for hotspot
Queries per second
Google Search 60K qps

SLA - Service-Level Agreements

99.9 (3 nines) 99.999 (5) 99.9999 (6)
Daily 86s 0.86s 0.086s
Monthly 43m 28s 26s 2.6s
Yearly 8h 41m 38s 5m 13s 31s

o MTTD: Mean Time to Detection o MTBF: Mean Time Between Failures o MTTR: Mean Time To Respond / Recover

High-Level Architecture

API Definition

  • Translate Functional Requirements into API Calls (only interface)
  • Triggered by API call or BATCH processing?
  • Public API vs. internal API

Architectural Components in general

  • Memcache
    • Caching Strategy: LRU
  • Load Balancer
  • Message Queue
  • Timeseries DB
  • Relational DB
  • Key-Value Store

Security

  • Authentication
  • IDOR
  • SSRF (in case of CDN)
  • CSFR
  • XSS

Deep Dive into individual service

Prepare:

  • Quad Tree
  • Reverse Index