Lilly Tech Systems
API & System Coding Challenges
The systems interview format: build real infrastructure components in code. REST APIs with authentication and pagination, rate limiters using token buckets and sliding windows, LRU and LFU caches, message queues with dead letter handling, and distributed patterns like consistent hashing and circuit breakers — all implemented from scratch in Python.
Your Learning Path
Follow these lessons in order to build every major system component from scratch, or jump to any topic you need to review.
1. System Implementation in Interviews
What system coding interviews expect, how they differ from whiteboard design, and the Python-first approach to building infrastructure components.
2. Build REST APIs
Implement CRUD APIs, pagination with cursors and offsets, authentication middleware with JWT, and structured error handling from scratch.
3. Implement Rate Limiters
Build fixed window, sliding window log, token bucket, and leaky bucket rate limiters. Understand trade-offs and when to use each.
4. Implement Caches
Build LRU cache with O(1) operations, LFU cache, TTL-based expiration cache, and write-through cache with consistency guarantees.
5. Queues & Pub/Sub
Implement an in-memory message queue, priority queue scheduler, pub/sub system with topics, and dead letter queue with retry logic.
6. Distributed Patterns
Implement consistent hashing for sharding, bloom filters for membership testing, circuit breakers for fault tolerance, and retry with exponential backoff.
7. Patterns & Tips
System implementation patterns, testing strategies for infrastructure code, common interview pitfalls, and a comprehensive FAQ.
What You'll Learn
By the end of this course, you will be able to:
Build Production-Grade APIs
Design and implement REST APIs with authentication, pagination, rate limiting, and proper error handling — the components every backend system needs.
Implement Core Infrastructure
Build rate limiters, caches, and queues from scratch using only Python standard library. Understand the data structures and algorithms behind each component.
Code Distributed Patterns
Implement consistent hashing, bloom filters, circuit breakers, and retry mechanisms. Turn whiteboard designs into working code.
Ace Systems Interviews
Answer the most common systems coding question: "Implement X from scratch." Confidently build any infrastructure component under interview pressure.