UsageFlow – Usage-Based Billing & Webhook Platform

UsageFlow is a multi-tenant SaaS platform that enables applications to track usage events, configure pricing plans, generate invoices, and deliver billing events to external systems via reliable webhooks. It is designed as a developer-first, production-oriented system, inspired by real-world billing platforms like Stripe.

📋 Table of Content

• 🚀 Key Features
• 🧠 Architecture Overview
• 🛠️ Tech Stack
• 🔐 Security Practices
• 📈 Why This Project Matters

🚀 Key Features

• Multi-Tenant Architecture
  • Organizations with role-based access control (RBAC)
  • Single active subscription per organization
• Usage Tracking
  • Secure ingestion via API keys
  • Event-based usage collection
• Flexible Pricing Engine
  • Metrics (API calls, users, etc.)
  • Plans with base price + per-metric overages
• Subscription & Invoicing
  • Plan activation per organization
  • Invoice generation per billing period
• Reliable Webhooks
  • Durable event storage
  • Background delivery with retries
  • Secure HMAC signature verification
  • Delivery logs & observability UI
• Audit Logging
  • Track all sensitive actions (plans, keys, subscriptions, webhooks)
• Background Workers
  • Usage aggregation
  • Invoice generation
  • Webhook delivery via BullMQ
• Validation using Zod

🧠 Architecture Overview

UsageFlow is built with a decoupled, event-driven architecture:

• Next.js App
  • Dashboard UI
  • Authenticated server actions
  • Public ingestion API
• PostgreSQL (Prisma)
  • Source of truth for all data
• Redis + BullMQ
  • Background job queue
• Worker Service
  • Usage aggregation
  • Invoice generation
  • Webhook delivery

🛠️ Tech Stack

• Frontend / Backend: Next.js (App Router), TypeScript
• Auth: NextAuth
• Database: PostgreSQL (Prisma ORM)
• Queue & Cache: Redis (BullMQ)
• Workers: Node.js + BullMQ Workers
• Deployment: Vercel (App), Railway / Render (Worker)

🔐 Security Practices

• API keys stored as hashed values
• Webhook secrets shown only once
• HMAC-signed webhook payloads
• Strict server-side RBAC enforcement
• No sensitive logic on the client

📈 Why This Project Matters

UsageFlow is not a CRUD app.

It demonstrates real SaaS engineering concepts:

• Multi-tenancy
• Event-driven systems
• Background processing
• Reliable webhooks
• Observability & auditability