Design Password Manager (1Password / LastPass) - System Design
A password manager looks like a trivial CRUD app. Store some login records, sync them across the user’s phone and laptop, auto-fill them …
Read MoreDesign Single Sign-On (SSO / OAuth Provider) - System Design
Single Sign-On sounds like a login screen. It is not. It is a token factory that a hundred applications trust, sitting at the center of an …
Read MoreDesign UPI / PhonePe (Real-Time Payments) - System Design
“Scan a QR, money leaves your HDFC account and lands in a shopkeeper’s SBI account in three seconds” sounds like one API call. It is not. …
Read MoreeBPF Makes Production Debugging Feel Like Cheating - A Practical Intro for App Engineers
The last time a service of mine went slow in production and the dashboards showed nothing, I did what every application engineer does: added …
Read MoreDesign a CAPTCHA Service - System Design
Everyone pictures a CAPTCHA as a picture of squiggly text. “Render some distorted letters, ask the user to type them, check the string, …
Read MoreDesign Reverse Image Search (Google Images) - System Design
Reverse image search looks like a search problem, and it is - but not the kind you get from an inverted index of words. A user hands you a …
Read MoreDesign Shazam (Audio Fingerprinting) - System Design
You hold your phone up to a speaker in a loud cafe, capture five seconds of a song you half-recognize, and a moment later the screen names …
Read MoreKafka Consumer Lag Is Lying to You - How to Measure and Fix It Properly
Every Kafka incident review I have sat in has the same slide near the end: a graph of consumer lag that stayed flat and green for the entire …
Read MoreDesign a Distributed Lock Service (ZooKeeper / etcd) - System Design
There is a small category of infrastructure that is boring on the surface and terrifying underneath: the thing that every other service …
Read MoreDesign Google Translate - System Design
Google Translate looks like a text box: you type “hello,” you get “hola,” done. That intuition survives one short sentence. The moment you …
Read MoreDesign S3 (Object Storage) - System Design
An object store looks like a hash map with two methods: PUT(key, bytes) and GET(key) -> bytes. That framing is exactly why it is hard. A …
Read MoreClickHouse Is Not Just for Big Data - When to Replace PostgreSQL for Analytics
Most teams do not choose ClickHouse. They run away from PostgreSQL until it stops working, panic, and reach for whatever managed analytics …
Read MoreDesign Apple Find My / Google Find My Device - System Design
Find My looks like a location-tracking problem and it is, but the interesting half is a paradox: you must locate a device that is offline - …
Read MoreDesign Snapchat / Instagram Stories - System Design
Stories look like a photo feed with a countdown, and people design them like one. That is the trap. A story is not a permanent post you …
Read MoreDesign Voice Assistant (Alexa) - System Design
You say “Alexa, what’s the weather in Bangalore tomorrow?” and about eight hundred milliseconds later a speaker on your kitchen counter says …
Read MoreDesign a Spam / Fraud Detection Pipeline - System Design
Everyone thinks fraud detection is a set of if statements. “Block logins from Nigeria, flag transactions over $5000, rate-limit signups per …
Read MoreDesign Gmail (Email Service Backend) - System Design
Email looks like a solved problem. It is 40 years old, the protocol fits on a napkin, and every framework ships a send_mail() in three …
Read MoreDesign Truecaller (Crowdsourced Caller ID) - System Design
An unknown number rings your phone and, before you pick up, the screen says “Rajesh Kumar - Reported as spam 240 times.” You have never …
Read MoreTool-Calling Patterns That Actually Work in Production AI Agents
Most agent tutorials show the same thing: define one tool, let the model call it once, print the result, declare victory. That is not an …
Read MoreCI/CD for AI Applications Is Different - What Changes When Your Logic Lives in a Prompt
A git commit does not capture what your AI application actually does. You can freeze every line of Python, tag the release, and deploy the …
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