Golang DDD Architecture

Use this skill to shape a Go service so it stays easy to change, test, and reason about as business logic grows.

Start Here

• Check whether the service is complex enough to justify the pattern.
• Keep the design smaller for simple CRUD or authentication flows where read and write shapes are mostly identical and business rules are thin.
• Use the full workflow when handlers keep growing if trees, models are reused across boundaries, or dependencies are hard to mock or untangle.

Workflow

1. Inventory entry points and use cases.

• Start from HTTP handlers, gRPC services, CLI commands, message consumers, and scheduled jobs.
• Rewrite the supported operations in business language before moving code around.

1. Draw the boundary map.

• ports are inbound transport and serialization only.
• app orchestrates use cases.
• domain owns business rules and invariants.
• adapters talk to databases, queues, external APIs, files, and other infrastructure.

1. Enforce dependency direction.

• domain depends on nothing outside itself.
• app may import domain but not concrete transport or adapter packages.
• ports and adapters may import inward layers.
• Fix import cycles by moving interfaces inward or by splitting responsibilities, not by flattening everything into one package.

1. Place interfaces next to the consumer.

• Define interfaces in the package that needs the behavior.
• Keep them narrow and use-case-oriented.
• Inject implementations from the composition root.

1. Separate models that change for different reasons.

• Do not reuse one struct for DB rows, API responses, Pub/Sub payloads, and domain state unless their change cadence is truly the same.
• Accept data duplication when it removes coupling. DRY is usually more valuable for behavior than for data.

1. Keep main boring.

• Use main as the composition root.
• Wire repositories, clients, handlers, and configuration there.
• Do not hide business logic, validation, or workflow branching there.

1. Leave the codebase more testable than you found it.

• Domain rules should be unit-testable without mocks.
• Application orchestration should be testable with tiny handwritten mocks.
• Adapter behavior should be covered with integration tests.

Use These References

• Read [references/architecture-rules.md](references/architecture-rules.md) for layer rules, package layouts, and anti-patterns.
• Read [references/naming-and-models.md](references/naming-and-models.md) when naming, model boundaries, or shared-struct tradeoffs are the hard part.

Deliverables

• a clear layer map or package plan,
• dependency direction that compiles without import-cycle hacks,
• constructors or wiring points in the composition root,
• explicit model boundaries,
• a short backlog of follow-up refactors if the system is too tangled for one pass.