API First Design

Importance of Information Hiding and Interface Design

• Emphasized the principle of information hiding in microservices design, especially not exposing internal domain data structures to external consumers.
• Highlighted the risk of leaky abstractions when teams directly expose their domain models.
• Stressed that the first integration step should be agreeing on the API or interface, whether it’s RESTful HTTP or a message-based pattern.
• Encouraged designing the interface or message schema before implementation begins.

Collaborative API Schema Definition

• Illustrated the need for cross-team collaboration when introducing new integrations, such as inventory and customer service systems in an e-commerce example.
• Both teams collaborated briefly to define and agree on the schema for messages/events before implementation started.
• Noted that this approach creates a contract between systems, allowing parallel, decoupled development.
• The process works for both synchronous (REST APIs) and asynchronous (event-driven) integration patterns.

Benefits of Contract-First Approach

• Allows independent progress for different teams because each knows the interface contract.
• Supports asynchronous workflows, where it doesn’t matter which team finishes first.
• Ensures that interfaces remain flexible, scalable, and more consumable as system requirements change.
• Instills a mindset that designs for external exposure by default, leading to better crafted APIs and contracts.

Suggested Action Items

• Always collaborate with integration partners to define schemas/contracts before building integrations.
• Document agreed-upon interfaces or schemas to ensure clarity and long-term maintainability.
• Apply the contract-first approach both for internal and external/API integrations.