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 included in 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, which store the changes and allow the processing of these items in independent reconciliation threads (go routines). Such a design allows sequential processing of the changed items and avoids conflicts.

The following namespaced custom resources have been defined to be reconciled by the CAP controller:

• CAPApplication: defines a high-level application, its domains, and the consumed SAP BTP services
• CAPApplicationVersion: defines a child resource of the CAPApplication, which contains container images that will be used to deploy application components (workloads) of a specific version
• CAPTenant: represents a child resource of the CAPApplication which corresponds to an SAP BTP subaccount subscribed to the application
• CAPTenantOperation: represents a provisioning, deprovisioning, or upgrade operation on a tenant that is 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.