The role of controller-runtime manager in Kubernetes operators

In a Kubernetes environment, the controller-runtime manager plays a pivotal role in efficiently managing resources through controllers and operators, offering an alternative to client-go. This package is integral to projects like Kubebuilder and Operator SDK, simplifying the creation of Kubernetes operators by implementing minimal requirements for starting with Kubernetes controllers. Controllers and operators in Kubernetes observe resources such as Deployments to ensure they conform to desired states, with operators being application-specific controllers like the Prometheus operator. The architecture of these controllers involves observing resources, informing events, maintaining a local cache, and using work queues for reconciliation. The controller-runtime manager coordinates shared dependencies such as clients and caches, ensuring optimal performance by utilizing a shared cache for all registered controllers. This framework allows the efficient management of Kubernetes resources by reducing the load on the Kubernetes API server. The manager oversees the operation of controllers, ensuring they effectively manage resources like Pods, and is crucial for the operation of operators, integrating with components including webhooks, metric servers, and leader elections.