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The Cluster Bundle: Declarative Kubernetes Cluster Management
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README.md

Cluster Bundle

GoDoc

Note: This is not an officially supported Google product

The Cluster Bundle is a Kubernetes-related project developed to improve the way we package and release Kubernetes software. It was created by the Google Kubernetes team, and was developed based on our experience managing Kubernetes clusters and applications at scale in both GKE and GKE On-Prem.

It is currently experimental (Pre-Alpha) and will have frequent, breaking changes until the API settles down.

Installation

Most users will interact with Cluster Bundle objects via the command line interface bundlectl.

To install, run:

go install github.com/GoogleCloudPlatform/k8s-cluster-bundle/cmd/bundlectl

Packaging in the Cluster Bundle

Packaging in Cluster Bundle revolves around a new type, called the Component:

  • Component: A versioned collection of Kubernetes objects. A component should correspond to a logical application. For example, we might imagine components for each of Etcd, Istio, KubeProxy, and CoreDNS.
  • ComponentBuilder: An intermediate type that allows for easier creation of component objects.

The Cluster Bundle APIs are minimal and focused on the problem of packaging Kubernetes objects into a single unit. It is assumed that some external deployment mechanisms like a command line interface or an in-cluster controller will consume the components and apply the Kubernetes objects in the component to a cluster.

Components

Here's how you might use the Component type to represent Etcd:

apiVersion: bundle.gke.io/v1alpha1
kind: Component
spec:

  # A human readable name for the component.
  componentName: etcd-component

  # SemVer version for the component representing any and all changes to the
  # component or included object manifests. This should not be tied to the
  # application version.
  version: 30.0.2

  # A list of included Kubernetes objects.
  objects:
  - apiVersion: v1
    kind: Pod
    metadata:
      name: etcd-server
      namespace: kube-system
    spec:
      containers:
      - command:
        - /bin/sh
        - -c
        - |
          exec /usr/local/bin/etcd
    # ... and so on

Some notes about components:

  • Components have a name and version. The pair of these should be a unique identifier for the component.
  • Objects must be Kubernetes objects -- they must have apiVersion, kind, and metadata. Other than that, there are no restrictions on what objects can be contained in a component.

You can see more about examples of components in the examples directory.

Building

To make it easier to create components, you can use the ComponentBuilder type:

apiVersion: bundle.gke.io/v1alpha1
kind: ComponentBuilder

componentName: etcd-component

version: 30.0.2

# File-references to kubernetes objects that make up this component.
objectFiles:
- url: file:///etcd-server.yaml

ComponentBuilders can be built into Components with:

bundlectl build --input-file=my-component.yaml

During build, objects are inlined, which means they are imported directly into the component.

Raw-text can also be imported into a component. When inlined, this text is converted into a ConfigMap and then added to the objects list:

apiVersion: bundle.gke.io/v1alpha1
kind: Component
spec:
  canonicalName: data-blob
  version: 0.1.0
  rawTextFiles:
  - name: data-blob
    files:
    - url: file:///some-data.txt

Patching

The Cluster Bundle library provides a new type called the PatchTemplate to perform Kustomize-style patching to objects in component. These are Go-templates that are applied to the objects in a component via StrategicMergePatch or, if the object is not a Kubernetes Object, via JSONPatch.

For example, if you have the following PatchTemplate specified as an object in a component:

apiVersion: bundle.gke.io/v1alpha1
kind: PatchTemplate
template: |
  apiVersion: v1
  kind: Pod
  metadata:
    namespace: {{.namespace}}

and the following Kubernetes object in the same component:

apiVersion: v1
kind: Pod
metadata:
  name: etcd-server
spec:
  containers:
  - command:
    - /bin/sh
    - -c
    - |
      exec /usr/local/bin/etcd
  # etc...

and you specified following options YAML file:

namespace: foo-namespace

Then, running the bundlectl command like so:

bundlectl patch --input-file=etcd-component.yaml --options-file=options.yaml

produces:

apiVersion: v1
kind: Pod
metadata:
  name: etcd-server
  namespace: foo-namespace
spec:
  containers:
  - command:
    - /bin/sh
    - -c
    - |
      exec /usr/local/bin/etcd
  # etc...

For more examples of Patching and Patch-Building, see the examples directory.

Options Schema for PatchTemplates

Additionally, you can provide an OpenAPIv3 schema to validate and provide defaults for options applied to patch templates. Extending the example above, we can provide defaulting and validation for our namespace parameter.

apiVersion: bundle.gke.io/v1alpha1
kind: PatchTemplate
template: |
  apiVersion: v1
  kind: Pod
  metadata:
    namespace: {{.namespace}}
optionsSchema:
  properties:
    namespace:
      type: string
      pattern: '^[a-z0-9-]+$'
      default: dev-ns

Here, we require the namespace parameter to be a string that must match the regex pattern. Additionally, if the namespace parameter is not supplied, then we default namespace to dev-ns.

Filtering

bundlectl can filter objects from a component, which allows for powerful chaining of the bundlectl command.

# Filter all config map objects
bundlectl filter -f my-component.yaml --filterType=objects --kind=ConfigMap

# Keep only config map objects.
bundlectl filter -f my-component.yaml --filterType=objects --kind=ConfigMap --keep-only

Component Testing

The Cluster Bundle library provides experimental support for testing building, patching, and validating components, by writing YAML test-suites that are run via go test.

To write a component test suite, create a YAML test file like so:

componentFile: etcd-component-builder.yaml
rootDirectory: './'

testCases:
- description: Success
  apply:
    options:
      namespace: default-ns
      buildLabel: test-env
  expect:
    objects:

    # The kind + the name references a unique object in the component.
    - kind: Pod
      name: etcd-server

      # ensure that the generated 'etcd-server' object YAML has the following
      substrings
      findSubstrs:
      - 'build-label: test-env'
      - 'image: k8s.gcr.io/etcd:3.1.11'
      - 'namespace: default-ns'

      # ensure that the generated 'etcd-server' object YAML does not have the
      # following substrings
      notFindSubstrs:
      - 'build-label: dev-env'

- description: 'Fail: parameter missing'
  expect:
    # Check for an error condition during the apply-process.
    applyErrSubstr: 'namespace in body is required'

Then, you need only write the following go boilerplate:

package component

import (
	"testing"

	"github.com/GoogleCloudPlatform/k8s-cluster-bundle/pkg/testutil/componentsuite"
)

func TestComponentSuite(t *testing.T) {
	componentsuite.Run(t, "test-suite.yaml")
}

Running the tests can be performed by running go test.

Examples:

Public APIs and Compatibility.

During pre-Alpha and Alpha, breaking changes may happen in any of the types in pkg/apis, the bundlectl CLI, or the Go APIs (methods, structs, interfaces not in pkg/apis).

During Beta, backwards incompatible breaking changes in the bundlectl and the pkg/apis directory will only happy during Major version boundaries.

The Go APIs are not covered by any compatibility guarantee and can break in backwards incompatible ways during any release

Development

Directory Structure

This directory follows a layout similar to other Kubernetes projects.

  • pkg/: Library code.
  • pkg/apis: APIs and schema for the Cluster Bundle.
  • pkg/client: Generated client for the Cluster Bundle types.
  • config/crds: Generated CRDs for the ClusterBundle types.
  • examples/: Examples of components
  • cmd/: Binaries. This contains the bundlectl CLI tool.

Building and Testing

The Cluster Bundle relies on Bazel for building and testing, but the library is go-gettable and it works equally well to use go build and go test for building and testing.

Testing

To run the unit tests, run

bazel test ...

It should also work to use the go command:

go test ./...

Regenerate BUILD files

To make using Bazel easier, we use Gazelle to automatically write Build targets. To automatically write the Build targets, run:

bazel run //:gazelle

Regenerate Generated Code

We rely heavily on Kubernetes code generation. To regenerate the code, run:

hacke/update-codegen.sh

If new files are added, you will need to re-run Gazelle (see above).

Prow

We use prow to test the Cluster Bundle. If the prow-jobs need to be updated, see the Cluster Bundle Prow Jobs:

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