Microsoft L65 Interview Experience
Summary
I interviewed for a Senior Backend / Ads / Distributed Systems role at Microsoft, navigating 5 rounds that thoroughly assessed my skills in coding, system design, and behavioral aspects, including deep dives into advertising, payment systems, and analytics.
Full Experience
Interview Experience – Senior Backend / Ads / Distributed Systems (5 Rounds)
🔹 Round 1 – Coding + Ads Fundamentals
Focus Areas:
- Project deep dive
- 3–4 behavioral questions
- Complete Ads ecosystem explanation
- Advertiser → DSP → Ad Exchange → SSP → Publisher
- Real-time bidding (RTB) flow
- Ranking & auction basics
- End-to-end ad serving lifecycle
Coding Question:
- Map of Map encoding problem
- Required graph search
- Implemented, executed, and discussed optimizations
🔹 Round 2 – Ads HLD + Search + ML
1️⃣ Design HLD for Microsoft Bing Ads
Designed high-level architecture similar to Microsoft Bing Ads.
Covered:
- Campaign setup & management
- Budget pacing
- Ranking logic & quality score
- Auction mechanism
- Publisher integration via SSP
- End-to-end ads delivery flow
2️⃣ Search API Design
Problem:
Design an API for: “Plumbers near Kondapur”
Discussion Points:
- Data ingestion pipeline
- Indexing (inverted index + geo-spatial indexing)
- Semantic matching
- Hybrid retrieval (BM25 + embeddings)
- Ranking signals & personalization
3️⃣ ML & LLM Discussion
- Random Forest vs SVM
- RAG (Retrieval-Augmented Generation) with LLMs
- Trade-offs: classical ML vs LLM-based systems
- Agentic frameworks for automation in ads optimization
🔹 Round 3 – Payment System Design (Razorpay-like)
Designed a payment gateway system similar to Razorpay.
Covered:
Payment Flow
- App → Gateway → Bank
- OTP handling
- 3DS flow
- Callback/webhook handling
Reliability & Safety
- Idempotency keys
- Retry mechanisms
- Handling bank timeouts
- Double debit protection
System Concerns
- DDoS protection
- Fraud detection
- Rate limiting
- Observability
Integration & UX
- Integration across app, gateway, and bank APIs
- Localization & language support
- UI rendering based on user country/currency
🔹 Round 4 – Hiring Manager + Bar Raiser (Onsite)
System Design: Website Activity Analytics
Requirement:
- Track clicks/actions/users
- 18-month lookback
- 5-minute granularity
- Filter by language, country, and other attributes
Discussion Points:
- Event-based schema (fact + dimension tables)
- SQL vs Time-Series DB
- Partitioning strategy & pruning
- Logged-in vs logged-out user tracking
- Data pipelines & SLAs
Advanced Topics
- Bloom Filters
- Count-Min Sketch
- Hashing in Redis
- Sampling & standard deviation use cases
- Transformer architecture basics
- Effect of Temperature, Top-K, Top-P on LLM outputs
- AI tool adoption metrics & measuring agentic AI impact
🔹 Round 5 – (LLD) - Onsite
Coding on Whiteboard
- LRU Cache (write code on board)
System & Behavioral Discussion
- Eviction strategies
- Caching trade-offs
- Reason for leaving
- Leadership & conflict handling
- Notice period expectations
Interview Questions (6)
Map of Map Encoding Problem
I was given a map of map encoding problem that required graph search. I had to implement the solution, execute it, and discuss optimizations.
Design High-Level Architecture for Microsoft Bing Ads
I was asked to design a high-level architecture similar to Microsoft Bing Ads. This included campaign setup & management, budget pacing, ranking logic & quality score, auction mechanism, publisher integration via SSP, and the end-to-end ads delivery flow.
Design Search API for Local Services
I needed to design an API for the search query: 'Plumbers near Kondapur'. Discussion points included data ingestion pipeline, indexing (inverted index + geo-spatial indexing), semantic matching, hybrid retrieval (BM25 + embeddings), ranking signals & personalization.
Design a Payment Gateway System (Razorpay-like)
I designed a payment gateway system similar to Razorpay. This involved detailing the payment flow (App → Gateway → Bank, OTP handling, 3DS flow, Callback/webhook handling), reliability & safety considerations (Idempotency keys, Retry mechanisms, Handling bank timeouts, Double debit protection), system concerns (DDoS protection, Fraud detection, Rate limiting, Observability), and integration & UX aspects (Integration across app, gateway, and bank APIs, Localization & language support, UI rendering based on user country/currency).
Design Website Activity Analytics System
The requirement was to design a system to track clicks/actions/users with an 18-month lookback and 5-minute granularity, allowing filtering by language, country, and other attributes. Discussion points included event-based schema (fact + dimension tables), SQL vs Time-Series DB, partitioning strategy & pruning, logged-in vs logged-out user tracking, and data pipelines & SLAs.
Implement LRU Cache
I was asked to implement an LRU (Least Recently Used) Cache on the whiteboard.