Secret Manager System Low-Level Design
What is a Secret Manager? A secret manager stores and distributes sensitive credentials (API keys, database passwords, TLS certificates, OAuth […]
Design, System Design
Algorithms, Coding Interview Questions, Heap
Two Heaps Interview Pattern
The Two Heaps Pattern Two heaps maintain the lower and upper halves of a data stream, allowing O(1) access to
Design, System Design
Webhook Delivery System Low-Level Design
What is a Webhook? A webhook is a user-defined HTTP callback. When an event occurs in a platform (payment succeeded,
Algorithms, Coding Interview Questions, Data Structures
Matrix Traversal Interview Patterns
Grid Traversal Fundamentals Most matrix problems involve: (1) BFS from one or multiple source cells, (2) DFS to explore connected
Design, System Design
Rate Limiting System Low-Level Design (Token Bucket, Leaky Bucket)
Why Rate Limiting? Rate limiting protects services from abuse, ensures fair usage, and prevents cascading failures from traffic spikes. Applied
Design, System Design
Invoice and Billing System Low-Level Design
Requirements Generate invoices for subscriptions and one-time purchases Support multiple billing cycles: monthly, annual, usage-based Apply discounts, taxes, and proration
Design, System Design
Multi-Region Architecture Low-Level Design
Why Multi-Region? Single-region deployments fail entirely during a cloud provider AZ or region outage. Multi-region provides: (1) High availability —
Design, System Design
Online Auction System Low-Level Design
Requirements Users can create auction listings with a start price, reserve price, and end time Users place bids; highest bid
Design, System Design
Content Feed System Low-Level Design
Requirements Generate a personalized feed of posts ranked by relevance/recency for each user Supports follow relationships: see posts from users
Design, System Design
Search Suggestions (Autocomplete) System Low-Level Design
Requirements Return top-k (k=10) query suggestions as a user types, within 100ms Suggestions ranked by search frequency or relevance score
Design, System Design
Location Tracking System Low-Level Design
Requirements Track real-time location of mobile assets (drivers, delivery couriers, field workers) 1M active devices sending location updates every 4
Design, System Design
Data Pipeline System Low-Level Design
What is a Data Pipeline? A data pipeline is a sequence of data processing steps: collect → transform → store
Algorithms, Coding Interview Questions, Data Structures
Ordered Map (TreeMap / SortedList) Interview Patterns
When to Use an Ordered Map (Sorted Dict / TreeMap) An ordered map maintains keys in sorted order with O(log
Design, System Design
Permission and Authorization System Low-Level Design
Permission Models Overview Three main models: ACL (Access Control List): per-resource list of who can do what. Simple, fine-grained, but
Design, System Design
Coupon and Discount System Low-Level Design
Requirements Create and manage discount coupons (percentage, fixed amount, free shipping) Apply coupon to a cart: validate, compute discount, prevent