Sample Controller in Java Using Fabric8 Kubernetes Client

Note

This repository implements a simple controller for watching Foo resources as defined with a CustomResourceDefinition (CRD).

This is a simple cont which implements a simple operator for a custom resource called Foo. Here is what this resource looks like:

apiVersion: samplecontroller.k8s.io/v1alpha1
kind: Foo
metadata:
  name: example-foo
spec:
  deploymentName: example-foo-deploy
  replicas: 1

Each Foo object would have a child Deployment which would have a specified number of replicas in Foo object, so this controller just tries to maintain Deployment for a Foo resource checking whether a Deployment which is owned by Foo resource is running in cluster or not.

How to Build

   mvn clean install

How to Run

Prerequisite: Since the sample-controller uses apps/v1 deployments, the Kubernetes cluster version should be greater than 1.9.

# create a CustomResourceDefinition
kubectl create -f src/main/resources/crd.yaml

# Run Controller
mvn exec:java -Dexec.mainClass=io.fabric8.samplecontroller.SampleControllerMain

# create a custom resource of type Foo
kubectl create -f src/main/resources/example-foo.yaml

# check deployments created through the custom resource
kubectl get deployments

Make Sure that Foo Custom Resource Definition is already applied onto the cluster. If not, just apply it using this command:

kubectl apply -f src/main/resources/crd.yaml

Once everything is set, you can see that controller creating Deployment in your cluster for Foo resource:

[main] INFO SampleController - trying to fetch item from workqueue...
[main] INFO SampleController - Got default/example-foo
[pool-3-thread-1] INFO SampleController - handleDeploymentObject(example-foo-deploy)
[main] INFO SampleController - trying to fetch item from workqueue...
[main] INFO SampleController - Got default/example-foo
[pool-3-thread-1] INFO SampleController - enqueueFoo(example-foo)
[pool-3-thread-1] INFO SampleController - Going to enqueue key default/example-foo
[pool-3-thread-1] INFO SampleController - Adding item to workqueue
[main] INFO SampleController - trying to fetch item from workqueue...
[main] INFO SampleController - Got default/example-foo
[main] INFO SampleController - trying to fetch item from workqueue...
[main] INFO SampleController - Work Queue is empty

Deploy to Kubernetes using Kubernetes Maven Plugin

You can use Kubernetes Maven Plugin to build and push image to a registry like this:

• Build and Push image to some registry. Before that you'll need to configure image.user and image.registry properties in pom.xml:

mvn k8s:build k8s:push -Djkube.build.strategy=jib

• Generate and Apply Kubernetes manifests to Kubernetes Cluster. First you'll need to configure ServiceAccount with correct roles. Otherwise, you might get 403 from Kubernetes API server. Since our application would be using default ServiceAccount, we can configure it like this:

kubectl create clusterrolebinding default-pod --clusterrole cluster-admin --serviceaccount=default:default

# In case of some other namespace:
kubectl create clusterrolebinding default-pod --clusterrole cluster-admin --serviceaccount=<namespace>:default

Then you can go ahead and run resource and apply goals:

mvn k8s:resource k8s:apply

Check pods after deployment:

sample-controller-java : $ kubectl get pods
NAME                                      READY   STATUS    RESTARTS   AGE
sample-controller-java-654d478c4f-qk84r   1/1     Running   0          2m38s

Create some Foo resource and check if Deployment gets created:

sample-controller-java : $ kubectl create -f src/main/resources/cr.yaml 
foo.samplecontroller.k8s.io/example-foo created
sample-controller-java : $ kubectl get pods
NAME                                      READY   STATUS              RESTARTS   AGE
example-foo-deploy-9bbb75dc8-6tkf8        0/1     ContainerCreating   0          2s
sample-controller-java-654d478c4f-qk84r   1/1     Running             0          3m36s