Designing Modular Service Boundaries

Modularity is not about having many repositories. It is about reducing coupling and preserving delivery speed.

Boundary rules I use

• Separate services by business capability, not by technical layer.
• Keep contracts explicit and versioned.
• Share as little runtime state as possible.
• Fail fast on contract drift.

Warning signs

• One service cannot deploy without three others.
• Every change requires synchronized releases.
• Teams cannot explain ownership in one sentence.

A modular system should make change easier, not harder.