As the architecture of Cloud Foundry on Kubernetes evolves, more and more components are shifting towards Kubernetes-native designs, with the objective of making CF more and more a first-class citizen in the Kubernetes ecosystem. A big part of this effort is centred around adopting the Kubernetes programming model, based on Custom Resource Definitions and controllers. Eirini has been one of the first components to do so. In this talk Giuseppe will give an overview of the Kubernetes programming model, describe how Kubernetes controllers work, and discuss the challenges the Eirini team faced while building a CRD-based API to replace their existing REST API.