Crossplane Split Architecture

The first issue we need to tackle is managing multiple provider configs for provider helm and Kubernetes. They need to be able to connect to the service clusters from the control cluster.

Connection details are only available on the control cluster. They are not propagated to the service clusters.

There are various services were the connection details are saved directly into the instance namespaces. By splitting the control cluster from the service cluster, this won’t be possible anymore. Instead of writing the connection details directly into the instance namespaces, we’ll have to wrap them into separate secrets and deploy them via provider-kubernetes.

The backend deletion protection webhooks need to be able to check against the composites on the control cluster.

So each of the service clusters also needs a connection back to the control cluster, in order for the webhooks to do the lookups.

By splitting the control clusters from the service clusters it gets even more important to cleanly differentiate between Crossplane Managed Resources and plain Kubernetes resources.

Managed resources need to always be deployed on the control cluster. They will not be available on the service clusters.

Usually those objects implement the resource.Managed interface. But unfortunately not all the objects do that, for example ProviderConfigs and Usages. Ideally the runtime should take care of wrapping objects automatically.