Design a system (initially one node/server) that could handle requests on the scale of millions. It should return a unique id for each request (The id should be unique in sense that there would be only one such id ever generated)

Functional requirements (FR)

Identify the primary actors and support their core create, read, update, and lifecycle actions.
Enforce the domain rules and constraints stated in the original prompt.
Provide appropriate search, status, history, or reporting capabilities for the use case.
Give operators a way to inspect failures and safely perform permitted administrative actions.

Define availability, latency, throughput, and growth targets from the intended workload.
Preserve data correctness during concurrent operations, retries, and dependency failures.
Protect user and business data with authentication, authorization, and auditable access.
Plan for observability, recovery, deployment safety, and cost as usage grows.

Define the scale, success measures, and operational ownership before committing to an architecture.
Compare at least two viable approaches and explain the trade-offs, migration path, and failure behavior.
Identify the riskiest assumptions and how you would validate them with data or a staged rollout.