Metered billing as durable, auditable workflows

The problem

Revenue operations — plans, quotas, usage aggregation, overage pricing, invoicing — had to be reliable and auditable. No lost usage, no double-counting, and safe to retry when something fails midway.

The approach

• ▸Built the whole billing pipeline as durable Temporal workflows with per-activity retryability, so a failure resumes instead of corrupting state.
• ▸Architected the backend around contract-based dependency injection across eight modules, with swappable in-memory adapters for isolated testing.
• ▸Validated inputs and money math with Zod schemas and a Vitest suite covering the edge cases that cost real money.

The outcome

• ✓Billing that survives crashes and retries safely — no lost or double-counted usage.
• ✓Clean module boundaries that make the system testable and cheap to change.
• ✓Usage aggregation, overage pricing, and invoice generation running as one auditable flow.

Stack