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Microsoft·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
May 2026

Summary

Microsoft system design round, one question about building a URL shortener from scratch. Pretty open-ended and they clearly wanted to see how far you'd push the architecture before they had to prompt you.

Questions Asked (1)

Q1

Design and architect a link shortening service similar to Bit.ly. Walk through the full system.

System DesignTechnical Trade-offsAPI & Integrations
Author's notes

I started with the basic encode/decode flow and felt pretty good about that part.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints (e.g., scale, read/write ratio, latency, custom aliases, analytics). Then propose a high-level architecture covering API design, data model, and key components like ID generation, storage, and caching. Finally, dive into trade-offs and optimizations for scalability and reliability.

Pro tip: Demonstrate awareness of Microsoft's emphasis on scalability and reliability by discussing how to handle hot keys and global distribution. Also, mention cost considerations and how to leverage cloud services like Azure for deployment.

1. Clarify Requirements

Ask questions to understand functional and non-functional requirements: expected traffic (e.g., 100M URLs/day), read/write ratio (e.g., 100:1), latency targets, custom aliases, expiration, analytics, and security.

2. High-Level Design

Outline the core components: API gateway, application servers, ID generator, database, cache, and analytics. Sketch the flow for shortening and redirecting URLs.

3. Deep Dive into Key Components

Discuss ID generation strategies (e.g., base62 encoding of auto-increment IDs, hash-based, or distributed counters), database schema (key-value store like Redis or Cassandra), and caching for hot URLs.

4. Scalability and Reliability

Address partitioning/sharding, replication, load balancing, and handling failures. Discuss how to avoid single points of failure and ensure low-latency redirects globally.

5. Trade-offs and Optimizations

Compare design choices (e.g., SQL vs NoSQL, pre-generation vs on-demand ID generation) and discuss optimizations like CDN, edge caching, and rate limiting.

Key Points to Mention

  • ID generation: base62 encoding, distributed unique ID generation (e.g., Snowflake), and collision avoidance.
  • Data storage: choice of database (e.g., DynamoDB, Cassandra) for high write throughput and low-latency reads; schema design.
  • Caching: using Redis or Memcached to cache hot URLs and reduce database load; cache eviction policies.
  • API design: RESTful endpoints for shortening and redirecting; handling custom aliases and expiration.
  • Scalability: sharding by key, replication for fault tolerance, and global distribution via CDN.
  • Analytics: asynchronous logging of click events for analytics without impacting redirect latency.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.