Comment System Low-Level Design
7 min read Requirements Users can post comments on content items (posts, videos, products) Threaded replies (nested comments) up to N levels deep […] Read article
System Design
System Design
Session Management System Low-Level Design
6 min read What is Session Management? Session management maintains the authenticated state of a user across multiple HTTP requests. HTTP is stateless Read article
System Design
Event Sourcing System Low-Level Design
7 min read What is Event Sourcing? In a traditional system, the database stores the current state: “Account balance = $500.” In event Read article
System Design
CI/CD Pipeline System Low-Level Design
7 min read What is a CI/CD Pipeline? CI (Continuous Integration): automatically build and test code on every commit. CD (Continuous Delivery/Deployment): automatically Read article
System Design
Email Delivery System Low-Level Design
7 min read Requirements Send transactional emails (password reset, order confirmation, notifications) and marketing emails (campaigns, newsletters) 100M emails/day, peak 10K/second during campaigns Read article
System Design
Cache System Low-Level Design (LRU, Write Policies, Redis Cluster)
7 min read Why Caching? A cache stores copies of frequently-accessed data in fast storage (RAM) to avoid expensive re-computation or round trips Read article
System Design
Log Aggregation System Low-Level Design
6 min read What is a Log Aggregator? A log aggregator collects logs from distributed services, normalizes them, stores them for search, and Read article
System Design
Secret Manager System Low-Level Design
7 min read What is a Secret Manager? A secret manager stores and distributes sensitive credentials (API keys, database passwords, TLS certificates, OAuth Read article
Algorithms, Coding Interview Questions, Heap
Two Heaps Interview Pattern
6 min read The Two Heaps Pattern Two heaps maintain the lower and upper halves of a data stream, allowing O(1) access to Read article
System Design
Webhook Delivery System Low-Level Design
6 min read What is a Webhook? A webhook is a user-defined HTTP callback. When an event occurs in a platform (payment succeeded, Read article
Algorithms, Coding Interview Questions, Data Structures
Matrix Traversal Interview Patterns
7 min read Grid Traversal Fundamentals Most matrix problems involve: (1) BFS from one or multiple source cells, (2) DFS to explore connected Read article
System Design
Rate Limiting System Low-Level Design (Token Bucket, Leaky Bucket)
6 min read Why Rate Limiting? Rate limiting protects services from abuse, ensures fair usage, and prevents cascading failures from traffic spikes. Applied Read article
System Design
Invoice and Billing System Low-Level Design
7 min read Requirements Generate invoices for subscriptions and one-time purchases Support multiple billing cycles: monthly, annual, usage-based Apply discounts, taxes, and proration Read article
System Design
Multi-Region Architecture Low-Level Design
6 min read Why Multi-Region? Single-region deployments fail entirely during a cloud provider AZ or region outage. Multi-region provides: (1) High availability — Read article
System Design
Online Auction System Low-Level Design
7 min read Requirements Users can create auction listings with a start price, reserve price, and end time Users place bids; highest bid Read article