Getting Started

This is a very simple hello world Kubernetes operator that used to demonstrate the basic functionalities and implementation details of an operator. The implementation of this operator based on the Operator SDK framework, a framework that generates all the boilerplate code of a Kubernetes operator and provides functionalities to build operators.

Prerequisites

Run the Operator

• kubectl v1.11.3+
• Kubernetes v1.11.3+ cluster

Build the Operator

• operator-sdk
• dep version v0.5.0+
• git
• go version v1.12+
• docker version 17.03+
• kubectl version v1.11.3+
• Kubernetes v1.11.3+ cluster

Configure a Kubernetes Cluster

As described in the prerequisites section, to run or build the operator we need to configure a Kubernetes cluster. There are multiple ways to configure a K8s cluster, therefore we can configure one of the following clusters.

• Minikube
• Docker for Mac
• Google Kubernetes Engine

Install the HelloWorld Operator

Install the prerequisites.

$ kubectl apply -f https://raw.githubusercontent.com/BuddhiWathsala/helloworld-k8s-operator/v0.4.0/deploy/crds/helloworld.io_helloworlds_crd.yaml
$ kubectl apply -f https://raw.githubusercontent.com/BuddhiWathsala/helloworld-k8s-operator/v0.4.0/deploy/service_account.yaml
$ kubectl apply -f https://raw.githubusercontent.com/BuddhiWathsala/helloworld-k8s-operator/v0.4.0/deploy/role.yaml
$ kubectl apply -f https://raw.githubusercontent.com/BuddhiWathsala/helloworld-k8s-operator/v0.4.0/deploy/role_binding.yaml

Install the operator deployment.

$ kubectl apply -f https://raw.githubusercontent.com/BuddhiWathsala/helloworld-k8s-operator/v0.4.0/deploy/operator.yaml

Deploy an Example

Here, we are going to deploy a HelloWorld example app that created

apiVersion: helloworld.io/v1alpha1
kind: HelloWorld
metadata:
  name: example-helloworld
spec:
  size: 1

Apply the HelloWorld example using the following command.

$ kubectl apply -f https://raw.githubusercontent.com/BuddhiWathsala/helloworld-k8s-operator/v0.4.0/deploy/crds/helloworld.io_v1alpha1_helloworld_cr.yaml

These commands will create the following Kubernetes artifacts in your cluster.

➜  ~ kubectl get pods
NAME                                      READY     STATUS    RESTARTS   AGE
example-helloworld-849865f49c-5cr2n       1/1       Running   0          84s
helloworld-k8s-operator-b46f79fb5-6kvq5   1/1       Running   0          112s

➜  ~ kubectl get svc
NAME                              TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)             AGE
example-helloworld                ClusterIP   10.106.176.32    <none>        8080/TCP            97s
helloworld-k8s-operator-metrics   ClusterIP   10.108.109.142   <none>        8383/TCP,8686/TCP   108s
kubernetes                        ClusterIP   10.96.0.1        <none>        443/TCP             4d19h

Send Requests

The Go application that we just deployed using this helloworld-k8s-operator, received HTTP GET requests and send the received payload back to the caller. Here we are using NGINX ingress controller to pass the requests to the service, so that first we need to setup the NGINX ingress controller in our Kubernetes cluster. To setup it please refer to this documentation.

Here, the helloworld operator, setup an ingress for the host called helloworld, therefore we need to set the external IP of the ingress with this hostname. To do that we can obtain the external IP of the ingress using the following command.

$ kubectl get ing

Note that, for minikube, the external IP is the minikube IP and we can get the minikube IP using the following command.

$ minikube ip

Now we can add the above host (helloworld) as an entry in /etc/hosts file.

Now, we can send requests to the deployed HelloWorld service from our local machine and the request URL is as follows.

$ curl http://helloworld/<CUSTOM_RESOURCE_NAME>/<MESSAGE>
$ curl http://helloworld/example-helloworld/HelloWorld

The deployed HelloWorld pod will log as follows.

➜  ~ kubectl logs -f `kubectl get pods | grep ^example-helloworld | awk '{print $1}'`
2020/05/07 11:07:37 START THE HELLO WORLD SERVER..!!
2020/05/07 11:09:26 Received message: HelloWorld

References

1. https://github.com/operator-framework/operator-sdk/blob/v0.17.0/website/content/en/docs/golang/quickstart.md
2. https://github.com/siddhi-io/siddhi-operator
3. https://kubernetes.github.io/ingress-nginx/deploy/