Design Affiliate Marketing System

Problem Statement: Affiliate Marketing Platform

An affiliate marketing platform pays partners (publishers) a commission for sales they drive to a merchant — and the engineering challenge is that it spans two systems with opposite requirements: a low-latency traffic layer (the click redirect a shopper hits) and an auditable financial layer (the commission ledger finance reconciles and pays out). Amazon Associates, CJ, and ShareASale all draw exactly this line, separating traffic acquisition from financial settlement.

The core flow: a publisher places a tracked URL, a shopper clicks it (the platform records the click and redirects to the merchant in milliseconds), the shopper later buys, the merchant fires a conversion event, the platform attributes that sale to the publisher's click, accrues a commission, and eventually pays out the accumulated commissions in a batch. The two halves never mix latency profiles: the redirect must be near-instant (a slow redirect loses the sale), while the settlement must be penny-perfect and auditable (finance pays real money to real partners).

The interviewer is listening for whether you treat the click stream as an append-only event log and the commission as a deterministic projection of those events under a versioned rule set — the same ledger discipline as loyalty and gift cards, applied to attribution. And whether you take attribution seriously as the hard problem: last-click versus multi-touch is a real debate, attribution windows (a 30-day cookie) matter, and fraud (cookie stuffing, self-referrals, click spam) is a first-class threat because affiliates are paid to drive traffic and some will game it.

The failure that defines the design: a shopper clicks an affiliate link in Safari, whose Intelligent Tracking Prevention blocks the third-party cookie, so the click is never recorded — and when the sale happens, no publisher gets credit. This 'lost last-click' is why modern affiliate tracking moves to first-party, server-side click recording, not browser cookies alone.