System Design

Interview-ready answer

I would separate the write path that creates a short code from the read-heavy redirect path. The API validates the destination, generates a unique code, and stores the mapping with expiry and ownership metadata. Redirects use a cache in front of durable storage, with careful handling for missing or expired codes. I would clarify traffic and reliability requirements first, then address abuse controls, analytics, and cache consistency.

Interview-ready answer

A rate limiter decides whether a request is allowed under a policy such as N requests per identity per time interval. I would place it at an API gateway or service boundary, choose an algorithm such as token bucket based on burst behavior, and use atomic state updates when limits are shared across instances. The design must define identity, response headers, storage failures, and whether temporary inconsistency is acceptable.