The Parnas Suite

The change request is supposed to affect just one field. Before Daniel Reeves has finished reading it, twenty-three teams have been invited to discuss the impact.

Daniel has spent years helping to build Meridian, a bank's modern customer platform. Its services have clear owners, its teams deploy independently, and its architecture follows the accepted principles. Yet ordinary changes require extraordinary coordination, and a screen can tell a customer something that no part of the system has established as true.

When three unusual external reviewers arrive, they ask questions Daniel thought he could answer. What does the system promise? Which decisions belong together? What is each boundary protecting? And how much of the complexity comes from the business itself?

The Parnas Suite is a story about software design inside a large organisation, where technical choices become entangled with deadlines, supplier contracts, professional reputations and careers. Through design reviews, production incidents and a small experiment, Daniel and his colleagues begin to reconsider ideas they have spent years defending. Their disagreements have consequences, and even a working design must survive the organisation that will maintain it.

Written for developers, architects and technical leaders, the book explores modularity, data, transactions, user interfaces and the knowledge needed to keep a system understandable. It returns to some of software engineering's foundational ideas and asks what happens when familiar principles become rules whose reasons nobody remembers.