Choose a style; keep the code easy to change

A small team sharing one transaction model may benefit from one deployable process with cohesive packages. Separate services become useful when independent scaling, ownership or delivery outweighs coordination costs. A folder named services does not make a monolith distributed, and a network hop does not make a boundary clean.

Early returns keep a short function focused on its successful operation. Names should explain domain meaning; return errors at the layer able to add useful context. Avoid a generic helper that hides the important policy decision from its caller.

Ask whether one business change requires edits across unrelated packages; whether error ownership is clear; whether interfaces have real consumers; and whether tests describe observable behavior instead of private function calls. Keep formatting with gofmt, document surprising contracts, and remove abstractions that do not pay for their indirection. No architecture style eliminates concurrency, capacity or consistency tradeoffs.

Monolith and microservices describe deployment and ownership boundaries. Layered, hexagonal, Clean and Onion describe responsibility and source dependencies. Vertical slices organize change around features; MVC organizes presentation. DDD is a modeling approach, CQRS separates write and read models, and event sourcing chooses a state history as authority. A modular monolith can use hexagonal ports, vertical slices and CQRS together. Record the quality goal before comparing scores.

First choose code organization: packages by capability, layers or vertical slices. Next choose state coordination: local transactions, asynchronous events or event history. Finally choose deployment topology: one executable, functions or independent services. These are different axes. A modular monolith can use hexagonal boundaries and CQRS; a microservice can still have tangled internal code. Describe the constraint a choice solves before comparing editorial ratings. Scores are scenario-specific recommendations, not performance measurements.

A useful decision record contains the workload, team ownership, correctness requirements, candidate approaches, chosen tradeoff and what evidence would reopen the decision. For a small team, one deployable with local transactions may beat independently deployable services despite an ambitious diagram. Revisit when measured scaling, fault isolation or team release independence becomes a constraint. Do not migrate because a style receives a higher score in a different scenario.

Review one request from input validation to durable effect and response. Who owns the transaction? Who retries? Where is authorization enforced? Which boundary receives a deadline, and which log identifies the operation without exposing credentials? Then inspect tests at these seams. Small functions alone cannot repair contradictory ownership or undefined failure recovery. Prefer the simplest architecture that makes the required guarantees testable and operationally understandable.