The programmatic way of writing a custom resource definition allows us to do a little bit more than the declarations. It lets us introuduce dynamic behavior. We do this by calling the methods from the client-go package for create, update and delete of the resource to use with Kubernetes API server. These methods are referred to as the ‘clientset’ because they use the corresponding methods from the Kubernetes apiextensions library. We connect to the API server from within the cluster using InClusterConfig method from the package. So far all of these methods are just calls with appropriate parameter and checks of return values.

With the example involving backup of user data, we have shown that the packing and unpacking of an archive can be described with a custom resource called Backup. This resource can then be scoped to the corresponding resource for whom the backup makes sense. The availability of the custom resource implies that we can use K8S API and CLI to request it.
We have also shown that that bytes of the backup can be inlined into the outgoing K8s representation from the api-server in both yaml and json format which allows the user to use such things as jsonpath to go directly to the archive data and download it as a file with standard command line arguments.
It is also possible to make the K8s API directly transfer the archive bytes with its own resource. This resource would then be decoded into a file. There is no limit on the bytes sent over the API response so the size of the archive can be arbitrary. It would be better that the preparation of the archive be decoupled from its transfer because the transfer might be interrupted. It is also important that the archive be properly cleaned up if it is persisted locally since they can be of any size.
Why is the scope and purpose of this custom resource for an archive important ? It helps the users’ data to be packaged from project to project regardless of what it comprises of and where it is stored – file, blob, stream. This portability of data independent from the logic and the platform improves mobility and productivity for the end-user.