RukPak

RukPak runs in a Kubernetes cluster and defines an API for installing cloud native bundle content.

Introduction

RukPak is a pluggable solution for the packaging and distribution of cloud-native content and supports advanced strategies for installation, updates, and policy. The project provides a content ecosystem for installing a variety of artifacts, such as Git repositories, Helm charts, OLM bundles, and more onto a Kubernetes cluster. These artifacts can then be managed, scaled, and upgraded in a safe way to enable powerful cluster extensions.

At its core, RukPak is a small set of APIs, packaged as Kubernetes CustomResourceDefinitions, and controllers that watch for those APIs. These APIs express what content is being installed on-cluster and how to create a running instance of the content.

Components

RukPak is composed of a few primary APIs: Bundle, Instance, and ProvisionerClass

Bundle

A Bundle represents content that needs to be made available to other consumers in the cluster. Much like the contents of a container image need to be pulled and unpacked in order for Pods to start using them, Bundles are used to reference content that may need to be pulled and should be unpacked. In this sense, Bundle is a generalization of the image concept, and can be used to represent any type of content.

Bundles do nothing on their own - they require a Provisioner to unpack and make their content available in-cluster. They can be unpacked to any arbitrary storage medium such as a PersistentVolume or ConfigMap. Each Bundle has an associated spec.class field which indicates the Provisioner that should be watching and unpacking that particular bundle type.

Example Bundle

apiVersion: core.rukpak.io/v1alpha1
kind: Bundle
metadata: 
  name: example-operator.v0.9.3
spec:
  class: rukpack.io/k8s
  refs:
  - file://content
  volumeMounts:
  - mountPath: /content
    configMap:
      name: local 
      namespace: plumbus

Instance

The Instance API points to a Bundle and indicates that it should be “active”. This includes pivoting from older versions of an active bundle. Instance may also include an embedded spec for a desired Bundle.

Much like Pods stamp out instances of container images, Instances stamp out an instance of Bundles. Instance can be seen as a generalization of the Pod concept.

The specifics of how an Instance makes changes to a cluster based on a referenced Bundle is defined by the ProvisionerClass and the Provisioner that is configured to handle that ProvisionerClass.

Example Instance

apiVersion: core.rukpak.io/v1alpha1
kind: Instance
metadata:
  name: resolved-654adh
spec:
  selector: 
    matchLabels:
      subscription: etcd-operator
  bundle:
    name: resolved-654adh
    spec:
      class: rukpack.io/k8s
      refs:
      - file://content
      volumeMounts:
      - mountPath: /content
        configMap:
          name: resolved-654adh-content
          namespace: olm

ProvisionerClass

ProvisionerClass defines a configuration for a Provisioner. Provisioners are controllers that understand Instance, Bundle, and ProvisionerClass APIs and take action.

Each Provisioner has a unique id. For example, a Provisioner that understands bundles composed of arbitrary Kubernetes YAML manifests can have the id: rukpack.io/k8s.

A ProvisionerClass specifies a specific configuration of provisioning (i.e. settings to interpret Instance and Bundle APIs). A Provisioner will only operate on Instance and Bundle objects that reference a ProvisionerClass that contain the provisioner’s unique id.

If this seems familiar, it is the same pattern that is used by StorageClass / PeristentVolume / PersistentVolumeClaim in Kubernetes. This design is meant to be extendable to support Bundles and Instances backed by different content sources.

Example ProvisionerClass

apiVersion: core.rukpak.io/v1alpha1
kind: ProvisionerClass
metadata:
  name: <good name>
provisioner: <unique id>
# parameters has no schema, is provisioner-specific
parameters: {}

Contributing

RukPak is a community-based open source project, and all are welcome to get involved.