Monolith vs Microservices: The Strangler Fig Migration Playbook

Decomposing an established enterprise monolith into microservices is one of the highest-risk undertakings an engineering leadership team can face. A naive "big bang rewrite" almost always fails due to creeping requirements and continuous business drift.

The Strangler Fig Architecture Pattern

The Strangler Fig pattern migrates functionality incrementally by placing an API Gateway or reverse proxy in front of the legacy application. New capabilities are implemented as microservices, and existing routes are systematically peeled away from the monolith until it can be safely decommissioned.

[Inbound Client Traffic]
                   |
           [Envoy API Gateway]
            /               \
  (Legacy Routes)       (Modernized Routes)
          /                   \
   [Legacy Monolith]      [New Microservices]
   [Relational DB]        [PostgreSQL / Kafka]

Handling Shared Data & Dual Writing

The hardest part of microservices decomposition is not the business logic—it is the database. When two services need access to customer or order data, avoid cross-service database queries. Instead, employ Change Data Capture (CDC) via Debezium and Kafka to stream updates asynchronously.

When to Stay on a Modular Monolith

Microservices introduce distributed system complexity: network latency, partial failure modes, saga transaction rollbacks, and distributed tracing overhead. If your team is under 25 engineers and your domain boundaries are still evolving, a clean, well-tested modular monolith in Go or TypeScript is often the superior architectural choice.

// Decision Matrix:
if (teamSize < 30 && domainIsFluid) {
    chooseArchitecture("Modular Monolith"); // High velocity, simple deployment
} else if (independentDeployabilityNeeded && highConcurrencyHotspots) {
    chooseArchitecture("Strangler Microservices"); // Scalable, bounded contexts
}