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Lessons (28)

• Edge, Platform & Frontend Delivery

  … Do not put database credentials or heavy, long-running work in an edge runtime just because it is …

• Premiere-Night Video Streaming

  … Serve video through CDN edges and regional shields. At a 99% byte hit ratio the origin still needs …

• Graphs: BFS & DFS

  … a set of nodes (vertices) connected by edges . mermaid flowchart LR A((Home)) --- B((Park)) A --- C((School …

• Design a URL Shortener

  … A disabled link must not remain served indefinitely from an edge cache. How to prove it worked Load …

• Networking, DNS and Traffic Routing

  … Monitor DNS TTL/propagation, edge health, connection errors, regional latency and uneven load. A DNS answer is not …

• DSA Interview Patterns Cheat Sheet

  … 2. Examples: work one normal example and one edge case by hand. 3. Brute force: say it out …

• Onion Architecture & Clean vs Hexagonal vs Onion

  … Infrastructure is at the edge and depends on the centre, through interfaces owned by the centre. ![The same …

• CloudFront: Faster Websites and Safer File Delivery

  … CloudFront can serve a cached copy from a nearby edge location. On a cache miss, it fetches the …

• Scaling, Load Balancing & Rate Limiting

  … 3. TLS termination: decrypt HTTPS at the edge, then use HTTPS or a private network to the backend …

• Linked Lists

  … The dummy head Many edge cases come from "what if I need to change the head?" A fake …

• Trees & Binary Search Trees

  … no children Edge The link between parent and child Depth of a node Number of edges from the …

• Serverless Architecture

  … concurrency for latency-critical paths, or edge runtimes (Cloudflare Workers, Vercel Edge) with near-zero cold starts. Designing …

• Prompting and Structured Outputs

  … show one or two examples when they clarify edge cases. Ask for structured output For application logic, prefer …

• AI Evaluation, Safety, and Security

  … Collect representative, permissioned examples that cover routine cases, edge cases, ambiguous input, and known failure modes. Keep evaluation …

• Node.js and Express

  … a larger app Keep HTTP details at the edge and business rules in plain functions you can test …

• Proxies, APIs and Real-Time Protocols

  … reverse proxy at the edge, request APIs, queues and persistent real-time connections](/img/system-design-l6/protocols …

• Caching & Redis

  … BC["Browser cache<br/ Cache-Control"] -- CDN["CDN edge<br/ images, JS, pages"] -- LB[Load balancer] -- App["App …

• Capacity Planning, SLOs and Error Budgets

  … schedule reliability work. Capacity review checklist Layer Ask --- --- Edge Can it absorb bots/assets and rate-limit fairly …

• Collaborative Document Editing & Real-Time Sync

  … ops + presence -- E[Edge / L7 LB<br/ route by docId] C -- REST: open, history, comments -- API[Doc API …

• Clean Architecture

  … business logic in the centre, infrastructure at the edges. When NOT to use it For a small script …

• Practical Lab: S3 File Upload and CloudFront Delivery with NestJS

  … If you do overwrite a file, force the edge to refetch: bash aws cloudfront create-invalidation --distribution-id …

• API Gateway, BFF & Service Discovery

  … API key TLS termination Handle HTTPS at the edge Request aggregation One client call → fetch from 3 services …

• Frontend Performance & Core Web Vitals

  … Faster server response (TTFB): cache HTML at the edge (SSG/ISR), use a CDN, speed up slow queries …

• Vertical Slice Architecture & the Modular Monolith

  … domain model in the centre + adapters at the edge. --- Part 2: The Modular Monolith The big idea An …

• 10,000 Users Do Not Need 10,000 Database Connections

  … open HTTP connections describes demand at the application edge. The pool size describes how much database work one …

• Backend Design Scenarios

  … Where does it live, and what happens if it goes down? Put enforcement at the edge or API …

• Domain-Driven Design: Strategic Design

  … and events cluster together, you've found the edges of bounded contexts (here: Ordering, Billing, Fulfilment). Strategic design …

• C4 Architecture Diagrams: Context, Container, Component and Code

  … Those details live at the edges, behind components with focused responsibilities. What belongs here—and what does not …