Adobe System Design: Scalable Subscription Management

You are asked to design a scalable backend subscription management system for a SaaS product that handles the complete subscription lifecycle: sign-ups, billing cycles, renewals, cancellations, upgrades/downgrades, and access enforcement.

Focus on a modular backend architecture with clear APIs for frontend clients and other services. Describe how you will integrate with payment gateways (e.g., Stripe) via webhooks and idempotent endpoints, store durable subscription and billing history, and emit events for downstream consumers (notifications, analytics, entitlement services). Explain how you will ensure strong consistency for billing operations (prevent double charges) while supporting high throughput and bursts.

High-level flow/stages you should cover:

• User-facing APIs: create/retrieve/modify subscriptions with idempotency, validation, and rate limiting.
• Payment integration: webhook handling, reconciliation, retries, and refund/proration rules.
• Billing scheduler: reliable cron/worker-based renewals with distributed locks to avoid duplicate billing.
• Event pipeline: publish subscription events to a message bus for notifications and access updates.
• Data persistence: transactional relational schema for subscriptions and billing ledger, plus read-replicas and partitioning for scale.

Skill signals to demonstrate: distributed systems design (scalability, partitioning), transactional integrity for billing, secure payment handling (PCI considerations, tokenization), API design (idempotency, error handling), observability (SLA metrics, reconciliation), and multi-tenant data modeling. Be prepared to discuss trade-offs (strong vs. eventual consistency), failure modes, and migration strategies for plan changes or billing logic.