pkg/runtime

This package contains a set of concrete structs and helper functions that provide a common controller implementation for an AWS service.

The top-level container struct in the package is ServiceController. A single instance of ServiceController is created (using NewServiceController()) from the cmd/controller/main.go file that contains the ACK controller entrypoint for a specific AWS service API.

ServiceController primarily serves as a way to glue the upstream sigs.k8s.io/controller-runtime (here on called ctrlrt for short since that alias we use in the ACK codebase to refer to that upstream repository) machinery together with ACK types that handle communication with the AWS service API.

The main ctrlrt types that ServiceController glues together are the ctrlrt.Manager and ctrlrt.Reconciler types. The ctrlrt.Manager type is used to bind a bunch of sigs.k8s.io/client-go and sigs.k8s.io/apimachinery infrastructure together into a common network server/listener structure. The ctrlrt.Reconciler type is an interface that provides a single Reconcile() method whose job is to reconcile the state of a single custom resource (CR) object.

The ServiceController.BindControllerManager() method accepts a ctrlrt.Manager object and is responsible for creating a reconciler for each kind of CR that the service controller will handle.

But how does the ServiceController know what kinds of CRs that it will handle?

There is a ServiceController.WithResourceManagerFactories() method that sets the ServiceController's collection of objects that implement the types.AWSResourceManagerFactory interface.

These resource manager factories produce objects that implement the types.AWSResourceManager interface, which is basic CRUD+L operations for a particular AWS resource against the backend AWS service API. The types.AWSResourceManagerFactory.For() method returns a types.AWSResourceManager object that has been created to handle a specific AWS service API resources for one AWS account. In this way, the single service controller can manage resources across multiple AWS accounts.

Resource manager factories are registered with a Registry object that is package-scoped to the individual service controller's services/{service}/pkg/resource package. See the example service's pkg/resource/registry.go file for how this package-scoped registry works. Individual resource manager factories are registered with this package-scoped Registry object using an init() call within a file named {resource}_manager_factory.go. For example, the Book resource in the example service's pkg/resource package has its resource manager factory registered in the init() function in the pkg/resource/book_resource_manager_factory.go file.