Migrating Monolithic ERP to Microservices Architecture
Decomposing a monolithic ERP system into microservices is a multi-year initiative that, when executed correctly, transforms a rigid, tightly-coupled codebase into independently deployable services that evolve at different speeds. The strangler fig pattern, where new microservices gradually replace monolith functionality while both systems coexist, is the only production-proven approach for ERP decomposition. Attempting a full rewrite is a known anti-pattern with a 70% failure rate.
Domain Decomposition for ERP Systems
ERP microservices decomposition follows domain-driven design (DDD) principles, identifying bounded contexts that map to business capabilities. In an ERP system, natural domain boundaries exist between Order Management, Inventory, Manufacturing, Finance, Procurement, and HR. Each bounded context becomes a candidate microservice with its own data store, API, and deployment lifecycle. The critical challenge is untangling shared database tables that span multiple domains.
- Map ERP modules to bounded contexts using event storming workshops with business stakeholders: identify where data ownership naturally belongs and where integration events cross boundaries
- Start with the least-coupled domain: typically Reporting/Analytics or Customer Portal, which read data from the monolith but rarely write back, minimizing two-way integration complexity
- Decompose the shared ERP database into per-service databases using the database-per-service pattern, with eventual consistency between services via domain events
- Define anti-corruption layers at each service boundary to translate between the legacy ERP data model and the new microservice domain models without contaminating either
- Plan for a 2-3 year migration timeline: extract 2-3 services per quarter, validate each extraction with production traffic, and iterate based on operational feedback
Implementing the Strangler Fig Pattern
The strangler fig pattern places an API gateway or routing layer in front of the monolithic ERP that selectively routes requests to either the legacy system or the new microservices. As each microservice reaches production readiness, the router shifts traffic from the monolith to the microservice. The monolith shrinks over time until it can be retired. This pattern keeps the existing ERP operational throughout the entire migration.
- Deploy an API gateway (Kong, AWS API Gateway, or Azure API Management) in front of the ERP monolith that routes 100% of traffic to the legacy system initially
- Extract the first microservice (e.g., Customer Service) with its own database, deploy it alongside the monolith, and route 10% of traffic to it for validation (canary deployment)
- Implement change data capture (CDC) using Debezium or AWS DMS to replicate data changes between the monolith database and microservice databases during the coexistence period
- Gradually increase traffic routing to each microservice: 10% canary, 25% validation, 50% parallel, 100% cutover, with automated rollback if error rates exceed 1%
Event-Driven Integration Between ERP Services
Microservices replacing ERP functionality must communicate asynchronously through domain events rather than direct API calls to avoid recreating monolithic coupling. An event bus (Apache Kafka, AWS EventBridge, or Azure Event Grid) carries domain events like OrderPlaced, InventoryAdjusted, and InvoicePosted between services. Each service publishes events when its domain state changes and subscribes to events from other domains it depends on.
- Deploy Apache Kafka ($0.10/hour on AWS MSK for kafka.t3.small) or AWS EventBridge ($1.00/million events) as the central event bus for inter-service communication
- Define a canonical event schema registry using Apache Avro or JSON Schema to ensure all services agree on event structure with backward-compatible schema evolution
- Implement the saga pattern for distributed transactions that span multiple services: e.g., a sales order creation saga coordinating inventory reservation, credit check, and order confirmation
- Design events as immutable facts with business meaning (OrderShipped, PaymentReceived) rather than technical CRUD operations (RecordUpdated, RowInserted) to enable future service evolution
- Build event replay capability so new microservices can reconstruct their state from the event log when first deployed, eliminating the need for complex data migration scripts
Netray AI agents map your ERP domain boundaries, generate microservice API contracts, and build event-driven integration patterns that keep your legacy ERP running during migration. Learn more.
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