Migrating 426 Nancy API endpoints to ASP.NET Core controllers

In 2021, Octopus Deploy transitioned its API framework from the outdated NancyFx to ASP.NET controllers to standardize and streamline its API development process. This decision addressed the confusion caused by a custom layer built on NancyFx and capitalized on the broader developer familiarity with ASP.NET. The migration process involved a strategic plan dubbed Derisk, Enable, Finish, which allowed both frameworks to coexist temporarily, facilitating a gradual transition. Initial tests showed improved performance with ASP.NET, and the team, consisting of four engineers, spent six months migrating 40% of the API endpoints. The migration strategy focused on derisking by analyzing, testing, and verifying endpoints, enabling by targeting less complex endpoints, and finishing by leveraging developer domain knowledge to continue migrations during routine changes. The process emphasized the importance of documentation, celebrating milestones, and collaborative efforts among the engineering team, acknowledging the complexity and repetitive nature of the task while highlighting the significant time investment required for such an undertaking.