Architecture Decisions › 📁 Core Architecture › ADR-0003: Adopt Microservices Architecture
ADR-0003
✓ Accepted Context Diagram

Adopt Microservices Architecture

Status

Accepted

Category

Core Architecture

Context

Our ShopFlow e-commerce platform has grown from a simple monolithic application to support multiple business domains including user management, product catalog, inventory, orders, payments, and shipping. The current monolithic architecture is experiencing several challenges:

Current Pain Points:

  • Deployment of any change requires full system deployment
  • Scaling individual components independently is impossible
  • Technology stack is locked to Java/Spring Boot across all domains
  • Team coordination overhead increases with team size
  • Database contention between different business functions
  • Outage in one component affects the entire platform

Business Requirements:

  • Support for 10x user growth over next 2 years
  • Faster time-to-market for new features
  • Different teams want to use different technology stacks
  • Need for independent scaling of high-traffic components (search, checkout)
  • Requirement for higher availability and fault isolation

We evaluated three architectural approaches:

  1. Continue with Monolith: Improve current architecture with better modularization
  2. Microservices: Decompose into separate services by business domain
  3. Modular Monolith: Hybrid approach with strong module boundaries

Decision

We will adopt a microservices architecture, decomposing our platform by business domains with clear service boundaries.

Target Architecture

C4Context title System Context - ShopFlow E-commerce Platform Person(customer, "Customer", "Shops for products online") Person(admin, "Admin", "Manages products and orders") System_Boundary(shopflow, "ShopFlow Platform") { System(web, "Web Application", "React SPA") System(mobile, "Mobile App", "React Native") System(gateway, "API Gateway", "Request routing and auth") System(user, "User Service", "Authentication & profiles") System(catalog, "Catalog Service", "Product information") System(inventory, "Inventory Service", "Stock management") System(cart, "Cart Service", "Shopping cart state") System(order, "Order Service", "Order processing") System(payment, "Payment Service", "Payment processing") System(shipping, "Shipping Service", "Delivery management") System(notification, "Notification Service", "Email/SMS alerts") } System_Ext(stripe, "Stripe", "Payment processing") System_Ext(shippo, "Shippo", "Shipping carriers") System_Ext(sendgrid, "SendGrid", "Email delivery") Rel(customer, web, "Browses products, places orders") Rel(customer, mobile, "Mobile shopping") Rel(admin, web, "Manages platform") Rel(web, gateway, "API calls", "HTTPS") Rel(mobile, gateway, "API calls", "HTTPS") Rel(gateway, user, "Authentication") Rel(gateway, catalog, "Product queries") Rel(gateway, inventory, "Stock checks") Rel(gateway, cart, "Cart operations") Rel(gateway, order, "Order management") Rel(gateway, payment, "Payment processing") Rel(gateway, shipping, "Shipping updates") Rel(payment, stripe, "Process payments") Rel(shipping, shippo, "Shipping APIs") Rel(notification, sendgrid, "Send emails")

Service Boundaries

  • User Service: Authentication, authorization, user profiles
  • Catalog Service: Product information, categories, search
  • Inventory Service: Stock levels, availability, reservations
  • Cart Service: Shopping cart state, session management
  • Order Service: Order lifecycle, order history
  • Payment Service: Payment processing, refunds
  • Shipping Service: Delivery options, tracking
  • Notification Service: Email, SMS, push notifications

Consequences

Positive:

  • Independent deployability enables faster release cycles
  • Teams can choose appropriate technology stacks for their domains
  • Individual services can be scaled based on demand
  • Fault isolation prevents cascading failures
  • Better alignment with business domains and teams
  • Easier to understand and maintain individual services

Negative:

  • Increased operational complexity (monitoring, deployment, networking)
  • Network latency between service calls
  • Data consistency challenges across service boundaries
  • More complex testing scenarios (integration, end-to-end)
  • Higher infrastructure costs initially
  • Need for new skills in distributed systems

Neutral:

  • Requires investment in DevOps tooling and practices
  • Team structure will need to align with service boundaries
  • Service communication patterns need to be established
  • Monitoring and observability become critical
  • Data migration strategy needed for existing monolith

Migration Strategy

  • Phase 1: Extract User and Notification services (low coupling)
  • Phase 2: Extract Catalog and Inventory services
  • Phase 3: Extract Order, Payment, and Shipping services
  • Phase 4: Extract Cart service and decompose remaining monolith
  • Maintain API compatibility during migration
  • Use Strangler Fig pattern for gradual migration

This ADR establishes our architectural foundation for scaling ShopFlow as a microservices platform.