Open Application Model is a specification for describing applications. Rudr is an implementation of the Open Application Model specification. Rudr runs on Kubernetes, though Open Application Model can be implemented on non-Kubernetes platforms.
Open Application Model is designed to introduce separation of concerns (SoC) into Kubernetes.
In Kubernetes today, developer information is freely intermingled with operator information. We wanted to create a way to distinguish between these two roles so that developers could deliver an artifact that describes their microservice, and operators could apply another artifact that configures and instantiates that microservice.
In the OAM model, a ComponentSchematic describes a developer's view of a microservice, and an ApplicationConfiguration describes an application operator's view of how a component is deployed into the cluster.
Rudr implements core workload types defined by OAM spec on Kubernetes platform, and also provides necessary utilities for implementing extension workloads/traits. In this sense, Knative is a promising implementation candidate for "serverless workload type" and "scale to zero" trait in Rudr. See related issue for more information.
Essentially, the OAM spec defines a set of concepts/rules to makes it easier for different components from different parties to compose as an application. For example, a developer could easily deploy an application composed by a Knative Serving instance consumes a AWS RDS instance by simply defining two components in OAM world.
You can describe existing applications as Open Application Model applications. See our migration guide.
Helm is a package manager for Kubernetes, and provides a way to package and distribute Kubernetes applications.
Open Application Model is just an application model that, thanks to Rudr, runs on Kubernetes. You can bundle your Open Application Model applications as Helm charts and deploy them using Helm. Here is an example of how to do that.
Kompose is a tool for manipulating Kubernetes YAML documents. It is also compatible with Open Application Model/Rudr.
Cloud Native Application Bundles (CNAB) is a format for packaging and distributing distributed applications, including applications created using OAM. For its part, OAM does not define or prescribe a packaging format. But it works well with CNAB (as well as with Helm).
When targeting more than one implementation of OAM, developers may find CNAB a better packaging fit than Helm.
Currently, all traits are built into Rudr. However, our plan is to make it possible for custom traits to be written and deployed into a Rudr cluster.
If you write a custom trait and integrate it with Rudr, consider opening a pull request. We are interested in adding more traits.
Currently, no. Scopes are fixed according to the Open Application Model spec.
Does Rudr support "extended workload types" as described in the Open Application Model specification
No. That section of the specification is a draft, and we are not yet supporting it.
On occasion, we have been asked why Rudr is written in Rust instead of Go. There is no requirement in the Kubernetes world that Kubernetes controllers be written in Go. Many languages implement the Kubernetes API and can be used for creating controllers. We decided to write Rudr in Rust because the language allows us to write Kubernetes controllers with far less code. Rust's generics make it possible to quickly and succinctly describe custom Kubernetes API resources without requiring developers to run code generators. And Rust's Kubernetes library can easily switch between Kubernetes versions with ease. We recognize that Rust might not be to everyone's taste (and neither is Go). However, we are confident that Rust is a solid choice for writing maintainable and concise Kubernetes applications.