Design a short link management platform for businesses (similar to Rebrandly or Short.io). Unlike a basic URL shortener, this system supports: custom branded domains (e.g., links.acme.com/sale), custom aliases chosen by the user, link expiration with configurable TTLs, password-protected links, A/B testing (one short link rotating between multiple destination URLs), and team-based access control. The platform serves 500 million redirects per day across 100,000 business accounts.
In your 90-second answer, cover: - Multi-tenant architecture supporting custom domains - How you route requests for thousands of custom domains to the correct tenant - Link expiration at scale (millions of links expiring daily) - A/B split routing logic and how you ensure statistical validity - Access control model for teams and link ownership
Constraints: redirect latency must be under 50ms at p99. Links must stop working within 60 seconds of expiration.
How to approach it
- Hint 1
Custom domains require wildcard DNS or a reverse proxy that maps incoming Host headers to tenant configurations -- think about how NGINX or Envoy can route based on the Host header.
- Hint 2
For sub-60-second expiration accuracy, you cannot rely on batch cleanup jobs. Consider storing expiry in the cache layer and checking it on every redirect request.
- Hint 3
A/B testing at the redirect layer means the routing service must be stateless but deterministic -- consider hashing the visitor identifier to assign a consistent variant.
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