Take the example of deploying serverless functions and a cloud based datastore (like CosmosDB) with a 3rd-party DNS service. Kubernetes operators are a poor fit for this, as they presume the existence of a Kubernetes cluster.
To me it looks like CNAB invents a new way of describing and deploying an application that looks nothing like a Kubernetes API while Crossplane is trying to use the existing Kubernetes API tooling to interoperate with and leverage that ecosystem.
Just because you are using a Kubernetes API doesn't mean you are presuming a Kubernetes cluster IMHO. The work being done with virtual kubelet[1] illustrates that.
So, I guess I am confused. You have users that want to package their app in containers, and run those containers. However, those users don't want to use Kubernetes APIs to do it? Why?
[1] https://docs.google.com/document/d/1RmHXdLhNbyOWPW_AtnnowaRf...
I know there's lots of love for Kubernetes, containers, and operators -- with me too. Still we can't and shouldn't presume the existence of Kubernetes or Kubernetes APIs to solve the problems CNAB is tackling.
"A bundle is comprised of a bundle definition and at least one invocation image. The invocation image's job is to install zero or more components into the host environment. Such components MAY include (but are not limited to) containers, functions, VMs, IaaS and PaaS layers, and service frameworks."
So, the very first step of CNAB is to run a container. And CNAB invents a new way of configuring, lifecycling, etc, this container image.
[1] https://github.com/deislabs/cnab-spec/blob/master/100-CNAB.m...
One of the examples we show is an electron app that provides a desktop installer experience for a cloud-based distributed application. We presume a container runtime for this.
We expect CNAB to play nicely with Kubernetes lifecycle management, but taking a hard dependency on Kubernetes was not deemed advantageous to CNAB's design goals.
Most of the examples are primarily container-based and the specification reflects that. We will definitely have to do a better job fleshing out the design with alternative invocation image types than OCI/docker. The azure-vm driver is one such (experimental) example.
Hope this helps!
But I see CNAB falling into the same trap as Helm, and many of the package managers before them (including newer variants with things like charm/juju), an archive with some notion of lifecycle events is not enough. Even though it's cute that lifecycle events are encapsulated in containers making it easier to manage their runtime dependencies.
What I think makes Crossplane's model more attractive is the notion of building on top of Kubernetes design and leveraging things like the operator pattern[2]. Now application stacks can do more interesting actions during their lifecycle, which can work to preserve availability during an event (like upgrading your application stack). Crossplane is about expanding the management of resources beyond just containers running in your cluster, but to any resource you can model in the K8s control plane and writing software that can react to events related to those resources.
[1] https://blog.upbound.io/introducing-crossplane-open-source-m... [2] https://coreos.com/operators/