operator-blueprint

OPERATOR BLUEPRINT

This repo contains an example of a custom kubernetes operator, made with kubebuilder.

References

NOTE: Before delving into the programming of kubernetes operators, a thorough knowledge of the functioning of k8s is recommended.

Useful references:

• kubernetes official docs
• kubebuilder official docs
• O'REILLY programming kubernetes

Prerequisites

• make
• kubectl
• docker
• kind
• go
• kubebuilder

Getting Started

You’ll need a Kubernetes cluster to run against.
You can use KIND to get a local cluster for testing, or run against a remote cluster.
Note: Your controller will automatically use the current context in your kubeconfig file (i.e. whatever cluster kubectl cluster-info shows).

The Makefile already contains all the functions that you need.
to see all make targets run:

make help

Running on the cluster

1. Install Instances of Custom Resources:

kubectl apply -f config/samples/

1. Build and push your image to the location specified by IMG:

make docker-build docker-push IMG=<some-registry>/operator-blueprint:tag

1. Deploy the controller to the cluster with the image specified by IMG:

make deploy IMG=<some-registry>/operator-blueprint:tag

Uninstall CRDs

To delete the CRDs from the cluster:

make uninstall

Undeploy controller

UnDeploy the controller from the cluster:

make undeploy

How it works

This project aims to follow the Kubernetes Operator pattern.
It uses Controllers, which provide a reconcile function responsible for synchronizing resources until the desired state is reached on the cluster.

This is a very simple vanilla operator, basically it does nothing more than deleting all the pods in the namespace specified in the CRD.
Let's take a look at the example manifest inside config/samples:

apiVersion: examples.stackzoo.io/v1alpha1
kind: PodBuster
metadata:
  labels:
    app.kubernetes.io/name: podbuster
    app.kubernetes.io/instance: podbuster-sample
    app.kubernetes.io/part-of: operator-blueprint
    app.kubernetes.io/managed-by: kustomize
    app.kubernetes.io/created-by: operator-blueprint
  name: podbuster-sample
spec:
  namespace: test

When you apply this manifest to the cluster (after deploying the operator) the custom controller will delete every pods inside the test namespace.

Test It Out

1. Start a local kind cluster:

make kind-up

1. Install the CRDs into the cluster:

make install

1. Prepare resources on the cluster:

make prepare-resources

1. Run your controller (this will run in the foreground, so switch to a new terminal if you want to leave it running):

make run

1. Apply the CRD manifest:

kubectl apply -f config/samples/examples_v1alpha1_podbuster.yaml

1. Check the operator logs in the first terminal:

2023-03-21T10:00:41+01:00	INFO	PodBuster - enter reconcile	{"controller": "podbuster", "controllerGroup": "examples.stackzoo.io", "controllerKind": "PodBuster", "PodBuster": {"name":"podbuster-sample","namespace":"default"}, "namespace": "default", "name": "podbuster-sample", "reconcileID": "f2d674c7-7ba0-45c8-92b8-2c1b384f6dc1", "req": "default/podbuster-sample"}
2023-03-21T10:00:41+01:00	INFO	PodBuster	{"controller": "podbuster", "controllerGroup": "examples.stackzoo.io", "controllerKind": "PodBuster", "PodBuster": {"name":"podbuster-sample","namespace":"default"}, "namespace": "default", "name": "podbuster-sample", "reconcileID": "f2d674c7-7ba0-45c8-92b8-2c1b384f6dc1", "PodBuster": {"apiVersion": "examples.stackzoo.io/v1alpha1", "kind": "PodBuster", "namespace": "default", "name": "podbuster-sample"}}
2023-03-21T10:00:41+01:00	INFO	PodBuster	{"controller": "podbuster", "controllerGroup": "examples.stackzoo.io", "controllerKind": "PodBuster", "PodBuster": {"name":"podbuster-sample","namespace":"default"}, "namespace": "default", "name": "podbuster-sample", "reconcileID": "f2d674c7-7ba0-45c8-92b8-2c1b384f6dc1", "Deleting pod": "busybox"}
2023-03-21T10:00:41+01:00	INFO	PodBuster	{"controller": "podbuster", "controllerGroup": "examples.stackzoo.io", "controllerKind": "PodBuster", "PodBuster": {"name":"podbuster-sample","namespace":"default"}, "namespace": "default", "name": "podbuster-sample", "reconcileID": "f2d674c7-7ba0-45c8-92b8-2c1b384f6dc1", "Deleting pod": "nginx"}
2023-03-21T10:00:41+01:00	INFO	PodBuster's status updated	{"controller": "podbuster", "controllerGroup": "examples.stackzoo.io", "controllerKind": "PodBuster", "PodBuster": {"name":"podbuster-sample","namespace":"default"}, "namespace": "default", "name": "podbuster-sample", "reconcileID": "f2d674c7-7ba0-45c8-92b8-2c1b384f6dc1", "status": true}
2023-03-21T10:00:41+01:00	INFO	PodBuster custom resource reconciled	{"controller": "podbuster", "controllerGroup": "examples.stackzoo.io", "controllerKind": "PodBuster", "PodBuster": {"name":"podbuster-sample","namespace":"default"}, "namespace": "default", "name": "podbuster-sample", "reconcileID": "f2d674c7-7ba0-45c8-92b8-2c1b384f6dc1"}

These logs tell you that your kubectl apply command triggered the controller reconciliation loop.

You can also inspect the status of the resources:

❯ kubectl describe podbuster podbuster-sample

Name:         podbuster-sample
Namespace:    default
Labels:       app.kubernetes.io/created-by=operator-blueprint
              app.kubernetes.io/instance=podbuster-sample
              app.kubernetes.io/managed-by=kustomize
              app.kubernetes.io/name=podbuster
              app.kubernetes.io/part-of=operator-blueprint
Annotations:  <none>
API Version:  examples.stackzoo.io/v1alpha1
Kind:         PodBuster
Metadata:
  Creation Timestamp:  2023-03-21T09:00:41Z
  Generation:          1
  Managed Fields:
    API Version:  examples.stackzoo.io/v1alpha1
    Fields Type:  FieldsV1
    fieldsV1:
      f:status:
        .:
        f:ok:
    Manager:      __debug_bin
    Operation:    Update
    Subresource:  status
    Time:         2023-03-21T09:00:41Z
    API Version:  examples.stackzoo.io/v1alpha1
    Fields Type:  FieldsV1
    fieldsV1:
      f:metadata:
        f:annotations:
          .:
          f:kubectl.kubernetes.io/last-applied-configuration:
        f:labels:
          .:
          f:app.kubernetes.io/created-by:
          f:app.kubernetes.io/instance:
          f:app.kubernetes.io/managed-by:
          f:app.kubernetes.io/name:
          f:app.kubernetes.io/part-of:
      f:spec:
        .:
        f:namespace:
    Manager:         kubectl-client-side-apply
    Operation:       Update
    Time:            2023-03-21T09:00:41Z
  Resource Version:  3758
  UID:               c081bcd9-d513-4227-bdd6-8dcb68276cbf
Spec:
  Namespace:  test
Status:
  Ok:    true
Events:  <none>

As you can see from the last lines, the status is OK: true

1. When you are done, delete the local kind cluster:

make kind-down

Modifying the API definitions

If you are editing the API definitions, generate the manifests such as CRs or CRDs using:

make manifests

License

Copyright 2023 stackzoo.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.