Overview
This case study demonstrates a minimal approach to platform-level contract design using two separate repositories:
- platform: a public, versioned contract repository
- contract-consumer: a separate repository that consumes those contracts in real code
No frameworks. No infrastructure. Just contracts and usage.
1. The problem: implicit contracts
In many systems, service boundaries are defined implicitly:
- API shapes live in controllers
- Event payloads are copied across services
- Error formats drift over time
This works until teams or services move at different speeds. The goal here was simple:
Make contracts explicit, versioned, and independently consumable.
2. Contract-first, not service-first
The platform repository contains only:
- Versioned contracts (contracts/v1)
- Event payload shapes
- Standard HTTP response formats
- Public error codes
- Lightweight runtime guards
What it explicitly does not contain:
- Business logic
- Framework code
- Environment or infrastructure details
Contracts are treated as stable artifacts, not implementation details.
3. Consumption as proof, not theory
A contract repository alone proves nothing.
The contract-consumer repository exists to answer one question:
Can a real service consume this without friction?
To validate this:
- The platform repo is consumed as a git submodule
- Contracts are imported as if they were an external package
-
A small handler-style function demonstrates:
- input validation
- error code usage
- trace propagation
- standard response shaping
This turns architectural intent into executable proof.
4. Reproducibility matters
The consumer repository is intentionally runnable by anyone:
- clean clone
- install dependencies
- run the example
Even environment edge cases (such as /tmp mounted with
noexec) are documented, because real systems fail in real
environments.
If a design cannot be reproduced, it cannot be trusted.
5. Why this structure scales
This approach scales not by adding complexity, but by adding clarity:
- New contract versions live alongside old ones
- Services choose when to upgrade
- Contracts change slower than implementations
- Consumers validate contracts by using them, not by reading docs
The result is not a framework, but a boundary.
Closing thought
Platforms do not fail because of missing abstractions. They fail because boundaries are unclear.
This case study shows that even a minimal, boring setup can dramatically improve how services communicate if contracts are treated as first-class citizens.