Migrating from monolith to microservices - lessons learned

Great write-up! We did a similar migration from a Rails monolith. A few additions:

Saga Pattern: For distributed transactions, we used the saga pattern with choreography (events) for simple flows and orchestration for complex multi-step processes. This was crucial for order processing where multiple services need to coordinate.

Event Sourcing: For critical data, we implemented event sourcing which gave us a complete audit trail and the ability to rebuild state. This was especially valuable during the migration to verify data consistency.

The most underrated advice: invest heavily in observability BEFORE breaking apart the monolith. You need distributed tracing (we used Jaeger) to debug issues across service boundaries.

14 months is actually pretty fast for that kind of migration. We took 2 years for a similar-sized project.

One pattern that saved us was the "Branch by Abstraction" approach. Instead of big-bang switching, we created abstraction layers in the monolith that could route traffic to either the old code or the new service. This let us migrate gradually and roll back instantly if something went wrong.

For data consistency, we ended up using the Outbox Pattern - writing events to a local outbox table in the same transaction as the data change, then publishing those events asynchronously. This gave us exactly-once delivery semantics.