Hey everyone,

I’m working on refactoring a very traditional, synchronously-designed service (think legacy monolith) into a set of modern microservices, and I keep hitting the same architectural wall: When is the complexity of Event-Driven Architecture (EDA) actually worth it over simple REST/gRPC?

In theory, EDA (Kafka, RabbitMQ, SQS/SNS) is the obvious winner for massive scalability, decoupling, and high throughput. But in practice, we all know the cost:

Debugging is a nightmare: Tracing a single user flow through 5 different asynchronous events across 3 different services requires intense observability tooling (and a prayer).

The Choreography Trap: When you need a guaranteed, immediate response from a chain of operations (e.g., “Charge Customer -> Update Inventory -> Send Confirmation”), managing that transactional consistency asynchronously requires implementing complex patterns like Sagas, which adds massive overhead.

We have a new internal service, the User Profile Aggregator, that needs to ingest data from 7 separate domain services and return one canonical JSON payload in < 100ms.

My question to the experienced programmers here:

For high-throughput, latency-sensitive aggregation tasks like this, do you prioritize:

A. The simplicity of Synchronous Fan-Out (The Aggregator service calls all 7 REST endpoints in parallel)? You risk tightly coupled services and long-tail latency, but the code is simple to debug.

B. The decoupling of Event-Driven Materialized Views (The Aggregator subscribes to all events and maintains its own local, eventually consistent DB)? You solve the latency and coupling issues, but you introduce consistency and debugging hell. 1.

Have you found a “sweet spot” hybrid pattern that minimizes the complexity of Sagas/Eventual Consistency?

Honestly, this kind of system design is where the real complexity of programming lives, and it’s almost impossible to solve with a simple Google search. If you are serious about digging into the concrete architectural patterns for scaling systems like this—with actual diagrams and solution blueprints—I highly recommend the conversations over at r/OrbonCloud. That community is really focused on sharing those deep, actionable solutions that go beyond the theory.