Service Boundaries and Ownership on Brian Faust

Boundaries Follow Work Without Becoming Destiny

Tue, 01 Oct 2024 00:00:00 +0000

We had a small team, so every service was officially owned by everyone. In practice, a developer could finish five hours of work in a specialist application and then spend three weeks integrating and testing it against the legacy API.

The delay was not a queue in front of another team. There was no other team. It came from a system which had evolved across years, changing commercial priorities, agencies, freelancers, and eventually an internal development team. Each period left decisions which made sense under its own pressure. Their combined cost appeared in the next change.

Enforce Architecture at the Cheapest Reliable Layer

Sun, 01 Sep 2024 00:00:00 +0000

The rule says Domain must not depend on Infrastructure.

Code review misses this reference:

final class Order extends \Illuminate\Database\Eloquent\Model
{
}

A quick substring scan catches it. The same scan also rejects a harmless docblock which names EloquentOrderRepository while explaining what Domain must not do.

The first check is unreliable because a person must notice every occurrence. The second is unreliable because text is not a PHP dependency. A token-aware source check catches the executable reference and ignores the prose.

Name the Independent Thing

Thu, 01 Aug 2024 00:00:00 +0000

Both diagrams say microservices.

The first has four HTTP endpoints and four repositories. They share one database, move on one release train, page one on-call rotation, and require a coordinated deployment when the shared schema changes.

The second can release Payments without Ordering, lose the Payments process without losing unrelated Ordering work, rotate payment credentials inside one data zone, and send repair to a staffed Payments owner.

The label is identical. The operating contract is not.

A Module Is Cheaper Than a Network Boundary

Mon, 01 Jul 2024 00:00:00 +0000

The payment was captured. Ordering does not know that.

Its request reached Payments, the capture became durable, and the response disappeared on the way back. Ordering now has a pending order and a timeout. Retrying without a stable identity may charge twice. Treating the timeout as a decline may abandon a real capture.

Inside one process and transaction, that particular ambiguity does not exist. The payment and order commit together or roll back together. Moving Payments across a network has bought a separate release and failure boundary. It has also replaced a return value with a protocol for identity, uncertainty, and repair.

Decompose by Change, Not by Layer

Sat, 01 Jun 2024 00:00:00 +0000

A cancellation rule changes: refuse cancellation after warehouse handoff.

In a conventional layered application, the work touches a controller, an application service, a domain policy, a repository, a migration, and tests. If the organization mirrors those directories, one business decision becomes a project for API, backend, and database teams.

The next change adds a covering index for order lookup. It touches only the persistence layer and changes no business decision.