At the core of the keynote is a deceptively simple challenge: can an application run without a user interface or a database? Cockburn uses this question to demonstrate how Ports & Adapters shifts the architectural focus toward the application core. By placing interfaces (ports) inside the application and keeping all technical implementations (adapters) outside, the business logic becomes independent of specific technologies.

The talk walks through concrete examples in Java and Ruby, illustrating how driving ports, driven ports, and their adapters interact. Cockburn emphasizes that adapters always live outside the application boundary – a detail that is frequently misunderstood in practice. This separation enables applications to replace databases, UIs, or external services without modifying the core logic, and without requiring extensive rewrites.

A recurring theme throughout the keynote is the role of tests. Cockburn argues that tests are not just consumers of the application, but its first and most important users. Automated tests, built against the ports of the application, are what ultimately prevent business logic from leaking into infrastructure code – and vice versa. Without such tests, architectural boundaries tend to erode over time, regardless of how clearly they are documented.

Key Takeaways:

1. Ports & Adapters focuses on inside vs. outside, not on layers
2. Interfaces for both driving and driven ports belong inside the application
3. Adapters always live outside the application boundary
4. Tests act as the first and most critical user of the system
5. Clear folder and package structures significantly support architectural clarity
6. The approach enables long-term evolution without rewriting the core

The keynote is aimed at software architects and developers working on long-lived systems who want to design software that can adapt to changing technologies while keeping the core stable.