From Monolith to Microservices: A 7-Step Migration Strategy

Rewriting a 10-year-old monolith from scratch is a recipe for disaster. It takes too long, and you lose business features during the rewrite. The "Strangler Fig" pattern is the only safe way to migrate critical systems.

The 7-Step Strategy

1. Identify Boundaries: Use Domain-Driven Design (DDD) to identify bounded contexts. The "User Profile" or "Notification" modules are usually good candidates to start.
2. Setup the Cloud Foundation: Build your Landing Zone in AWS/Azure with proper networking and security.
3. Create the Anti-Corruption Layer: Build an API Gateway that routes traffic. This allows you to switch traffic between the old monolith and the new microservice transparently.
4. Build the First Microservice: Extract the simplest module. Build it as a containerized service.
5. Shadow Traffic: Route real production traffic to the new service in "shadow mode" (fire and forget) to test performance without impacting users.
6. Cutover: Once confident, switch the API Gateway to route live traffic to the new service.
7. Decommission: Remove the old code from the monolith. Repeat.

Is it slow? Yes. Is it safe? Absolutely. We preserved 99.9% uptime for a regional retailer during a peak-season migration using this exact method.