Controller

The CAP controller uses client-go from Kubernetes, which provides the tools and utilities needed to interact with the Kubernetes API server and manage the custom resources defined by CAP Operator.

The controller uses Informers to watch certain resources and invokes registered event handlers when these resources are modified. To streamline the processing of such notifications, rate-limiting queues are implemented that store changes and allow processing of items in independent reconciliation threads (goroutines). This design enables sequential processing of changed items and avoids conflicts.

The following namespaced custom resources are reconciled by the CAP controller:

• CAPApplication: Defines a high-level application, its domains, and the consumed SAP BTP services.
• CAPApplicationVersion: A child resource of CAPApplication that contains container images used to deploy application components (workloads) of a specific version.
• CAPTenant: A child resource of CAPApplication that corresponds to an SAP BTP subaccount subscribed to the application.
• CAPTenantOperation: Represents a provisioning, deprovisioning, or upgrade operation on a tenant, scheduled as a child resource of a CAPTenant and executed as a sequence of specified steps.

Parent-child relationships between custom resources are established by defining owner references for the children.