Goldman Sachs System Design Interview: Design a Notification Service

A notification service takes a request from some other system ("tell this user their trade confirmation is ready") and turns it into a message the person receives. At a bank it's usually a shared internal platform. Many applications call it, and none of them want to run their own email and SMS plumbing. So the problem has two halves. The delivery half is the familiar one: queue the work, send through a provider, retry on failure. The platform half is what makes it interesting. Ten or fifteen apps share one pipe, so one misbehaving app can hurt all the others, and every app wants to know what happened to its messages.

The Goldman Sachs angle

Candidates report this prompt in Goldman's Superday Software Design and Architecture round, and sometimes in a VP hiring manager round, at every level from Analyst to VP. The framing varies by panel. Some candidates get the multi-tenant platform for 10 to 15 apps with email, SMS, a data model, the tech stack, the APIs and a reporting service. Others get a low-level version focused on classes, relationships and design patterns. One reported variant starts from the app side: a user submits a form, and you trace which APIs fire after Submit and how the result reaches them. Expect to be asked for the entities first. Candidates describe being asked to list them before anything else, and Goldman panels tend to drift into database choice, Kafka internals and Java concurrency wherever the design gives them an opening.

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