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Event-Driven Microservices Architecture

How to Architect a B2B Wholesale Marketplace

Architecting a B2B wholesale marketplace requires a robust, scalable, and flexible system to manage diverse vendors, complex pricing models, high-volume orders, and intricate logistics. An event-driven microservices approach enables independent development, resilient operations, and seamless integration with external systems essential for B2B transactions.

Recommended architecture pattern

Recommended tech stack

Frontend

Next.js (React) with TypeScript; Enables server-side rendering (SSR) for improved SEO and performance, crucial for product discovery, and provides a robust framework for complex UIs.

Backend

Node.js (TypeScript) with NestJS framework; Offers excellent performance for I/O-bound operations, ideal for API gateways and microservices, and TypeScript enhances code quality and maintainability.

Database

PostgreSQL with PostGIS extensions; Provides strong ACID compliance for transactional data (orders, users), flexible JSONB for semi-structured product attributes, and PostGIS for potential location-based logistics or vendor search.

Real-time / Messaging

Apache Kafka; High-throughput, fault-tolerant platform for real-time data streams and asynchronous communication between microservices, crucial for inventory updates, order status, and analytics.

Infrastructure

Kubernetes on AWS EKS; Provides robust container orchestration for microservices, ensuring high availability, scalability, and efficient resource utilization across environments.

Authentication

Auth0; Enterprise-grade identity and access management (IAM) platform, simplifying user authentication (SSO, MFA) and authorization for both buyers and sellers with role-based access control (RBAC).

Key third-party services

Stripe Connect for payments (escrow, payouts); Algolia for advanced product search and filtering; Twilio for SMS/email notifications (order updates, alerts); AWS S3 for media storage (product images, documents).

Core components

Key data model

Entity	Key fields	Notes
User	id, email, passwordHash, role, organizationId	index on organizationId, email
Organization	id, name, type (Buyer/Seller), address, contactInfo	index on name
Product	id, name, description, sku, vendorId, categoryId, attributes (JSONB)	index on vendorId, categoryId, sku
Inventory	id, productId, vendorId, quantityAvailable, location	unique index on productId, vendorId, location
PriceList	id, name, organizationId (buyer/seller), productId, minQuantity, maxQuantity, unitPrice	index on organizationId, productId
Order	id, buyerOrgId, vendorOrgId, status, totalAmount, shippingAddress, billingAddress, createdAt	index on buyerOrgId, vendorOrgId, status
OrderItem	id, orderId, productId, quantity, unitPrice, lineTotal	index on orderId, productId
Transaction	id, orderId, paymentGatewayRef, amount, status, type (payment/payout), createdAt	index on orderId, paymentGatewayRef

Core API endpoints

Method	Endpoint	Purpose
POST	/auth/login	Authenticate user and issue JWT.
POST	/organizations	Register a new buyer or seller organization.
GET	/products?category=X&vendorId=Y	Search and filter products with pagination.
GET	/products/{id}/pricing?buyerOrgId=Z&quantity=Q	Get dynamic pricing for a specific product and buyer.
POST	/orders	Create a new order with multiple line items.
GET	/orders/{id}	Retrieve details of a specific order.
PUT	/orders/{id}/status	Update order status (e.g., shipped, delivered).
PUT	/inventory/{productId}/adjust	Adjust inventory levels for a product.
GET	/vendors/{id}/products	Retrieve all products listed by a specific vendor.
POST	/rfq	Submit a Request for Quote.

Scaling considerations

• Real-time Inventory Updates: Implement event-driven updates via Kafka, using optimistic locking or sagas for complex inventory transactions across multiple vendors.
• Complex Pricing Calculations: Cache frequently accessed price lists and implement a dedicated, horizontally scalable pricing engine service to handle high-volume dynamic price lookups.
• High-Volume Order Processing: Utilize message queues (Kafka) to decouple order submission from processing, enabling asynchronous and resilient order fulfillment workflows.
• Advanced Product Search: Offload search functionality to a dedicated search engine (e.g., Algolia, Elasticsearch) for fast, faceted, and typo-tolerant queries, scaling independently from the database.
• Vendor Data Ingestion & Sync: Build robust data pipelines with message queues and ETL tools to handle batch and real-time synchronization from diverse vendor ERP/PIM systems.
• API Rate Limiting & Throttling: Implement API gateways with rate limiting to protect backend services from abuse and ensure fair usage across integrated vendor/buyer systems.

Security & compliance

• PCI-DSS Compliance: Use a PCI-compliant payment gateway (e.g., Stripe Connect) for all payment processing, avoiding direct handling or storage of sensitive cardholder data on internal systems.
• Data Privacy (GDPR/CCPA): Implement robust access controls, data anonymization/encryption at rest and in transit, and clear data retention policies for all user and organizational data.
• Role-Based Access Control (RBAC): Enforce granular permissions for different user roles (e.g., buyer, seller admin, sales rep) to ensure users only access authorized data and functionalities.
• Supply Chain Integrity: Implement robust vendor verification processes, audit logs for all critical actions (e.g., inventory adjustments, order status changes), and secure API integrations.
• Regular Security Audits & Penetration Testing: Conduct recurring third-party security assessments and penetration tests to identify and remediate vulnerabilities proactively.

Estimated monthly cost

Want a tailored build estimate? Try the free software cost estimator or the tech stack finder.

Suggested build plan

Phase	Timeframe	Deliverables
Phase 1: Foundation & Core Services	Weeks 1-12	User/Org management, Product Catalog MVP, Basic Order Placement, Auth0 integration, Infrastructure setup (IaC)
Phase 2: Marketplace & Vendor Enablement	Weeks 13-24	Advanced Product Catalog (attributes, media), Inventory Management, Dynamic Pricing Engine, Vendor Onboarding workflow, Payment Integration (Stripe Connect)
Phase 3: Advanced Features & Integrations	Weeks 25-36	RFQ system, Order Fulfillment workflows, Shipping integrations, Analytics dashboard, ERP/WMS integration APIs, Search optimization (Algolia)
Phase 4: Optimization & Scaling	Weeks 37-48	Performance tuning, Load testing, Disaster recovery planning, Advanced monitoring & alerting, Security hardening, New feature rollout process

Frequently asked questions

How do we handle complex B2B pricing models like tiered pricing, volume discounts, and custom contracts?

Implement a dedicated Dynamic Pricing Engine microservice. This service will ingest various pricing rules, buyer-specific contracts, and real-time inventory data to calculate the final price for any product and quantity, ensuring accuracy and flexibility.

What's the best way to integrate with diverse vendor ERP/WMS systems for inventory and order updates?

Establish an Integration Hub service utilizing an event-driven architecture (Kafka). Vendors can publish inventory updates or order statuses as events, and our system consumes them. For outbound, we can offer webhooks or APIs, tailoring integration points as needed.

How do we ensure data consistency and prevent race conditions with real-time inventory updates across multiple vendors?

Utilize an event-driven approach with a dedicated Inventory & Availability service. Inventory updates are published as events, and the service processes them sequentially. For critical operations like reservations, implement optimistic locking or sagas to ensure atomicity and consistency.

What are the key considerations for managing secure payments and vendor payouts in a marketplace?

Leverage a PCI-compliant payment gateway like Stripe Connect, which handles escrow, payment processing, and automated payouts to vendors. This minimizes your PCI burden and provides robust fraud detection and compliance features.

How can we provide a fast and relevant product search experience with a large and varied catalog?

Integrate with a specialized search service like Algolia or Elasticsearch. This allows for advanced indexing, faceted search, typo tolerance, and personalized results, providing a superior user experience compared to database-driven search.

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