helm-operator-example

A simple tutorial on how to create a Kubernetes Helm Operator ie. a Kubernetes Operator from a Helm Chart

What is a Helm Chart

A means of packaging up a collection of K8s specifications (such as yaml files) in a managed idempotent fashion. For example, a simple Helm Chart may contain deployment.yaml a service.yaml files with placeholders for number of replicas, name etc.

What is an Operator

By default, K8s comes with several exisiting resource Kind types. For example, some pre-packed native K8s resources are Deployment and Service. Basically, the contents of the Kind field in yaml spec. An operator is an example of a Custom Kind a.k.a. Custom Resource Definition (CRD) called what ever you want eg Foo, Bar, MyKind ... You get the idea.

What is a Helm Operator

A Helm Operator takes an existing Helm Chart as input and magicallly creates a CRD (say MyKind) out of it (that will need to be installed on the target K8s cluster). Then, the CRD can be operated upon as a first class K8s citizen eg kubectl create MyKind abcd

Benefits of creating a Helm Operator

• First Class K8s Citizen
• Can be managed using kubectl commands

Exammple

Objective

The following example describes how to create. install and use a Helm Operator from a Helm Chart

PreRequisites

• Install helm
• Install the operator sdk
• Login to your dockerhub account from the command line

Create a sample Helm application (using the standard Helm Nginx webserver example)

helm create nginx-app
helm package nginx-app

Create a Helm Operator from the Helm Chart

operator-sdk new my-nginx-operator --kind=MyNginx --type=helm --helm-chart nginx-app-0.1.0.tgz

Export your dockerhub username as a variable (makes running the following commands easier)

export DH_USER=<your dockerhub userid eg johnsmith>

Build the operator

cd my-nginx-operator
operator-sdk build $DH_USER/my-nginx-operator:0.1.0

Push the operator to a Docker repository (DockerHub, in this case)

docker push $DH_USER/my-nginx-operator:0.1.0

Set the correct Docker image in the generated operator.yaml file

sed -i "s|REPLACE_IMAGE|$DH_USER/my-nginx-operator:0.1.0|g" deploy/operator.yaml 

Install the Operator

Note: If your K8s cluster is on a separate machine, copy the deploy directory to the cluster master node

kubectl apply --validate=false -f deploy/crds/*_crd.yaml
kubectl apply -f deploy/operator.yaml
kubectl apply -f deploy/role_binding.yaml
kubectl apply -f deploy/role.yaml
kubectl apply -f deploy/service_account.yaml

Create an instance of MyNginx

• A usable sample specification of the MyNginx spec has been autogenerated at deploy/crds/charts.helm.k8s.io_v1alpha1_mynginx_cr.yaml

• Edit it as desired, for example, you may want to change the name (to "example-nginx") and the number of replicas (to 4).

sed -i "s|replicaCount: 1|replicaCount: 4|g" deploy/crds/*_cr.yaml
sed -i "s|name: example-nginx|name: example-nginx|g" deploy/crds/*_cr.yaml

• Apply the modified spec

kubectl apply -f deploy/crds/*_cr.yaml

Note: After applying the spec, if we chose to modify the name (and other fields) of the CR instance (say to "example-nginx-2") and re-apply the spec, 2 instances of the CR will be created ie. example-mynginx and example-mynginx-2 .

Validate the results

Note how we can address the CR Directly

$ ~/junk/my-nginx-operator/deploy/crds $ kubectl get MyNginx 
NAME              AGE
example-mynginx   11m

Note the operator deployment, and also a deployment for the sample Nginx service as a result of the CRD

$ ~/junk/my-nginx-operator/deploy/crds $ kubectl get deploy
NAME                        READY   UP-TO-DATE   AVAILABLE   AGE
example-mynginx-nginx-app   4/4     4            4           11m
my-nginx-operator           1/1     1            1           13m
....

Note that an Nginx is running at port 80

$ ~/junk/my-nginx-operator/deploy/crds $ kubectl get svc
NAME                        TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)             AGE
example-mynginx-nginx-app   ClusterIP   10.43.183.123   <none>        80/TCP              11m
...

We can connect to this server

$ ~/junk/my-nginx-operator/deploy/crds $ curl  http://10.43.183.123:80
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
.
.
<p><em>Thank you for using nginx.</em></p>
</body>
</html>

Note that there are 4 instances of Nginx running, as per our modifications

$ ~/junk/my-nginx-operator/deploy/crds $ kubectl get po
NAME                                         READY   STATUS    RESTARTS   AGE
example-mynginx-nginx-app-7dfc477d84-8857k   1/1     Running   0          11m
example-mynginx-nginx-app-7dfc477d84-9n5jt   1/1     Running   0          11m
example-mynginx-nginx-app-7dfc477d84-kpnvx   1/1     Running   0          11m
example-mynginx-nginx-app-7dfc477d84-z7h48   1/1     Running   0          11m
...

Cleanup

If we want to delete the instance of the CRD we just created, merely execute

$ ~/junk/my-nginx-operator/deploy/crds $ kubectl delete MyNginx example-mynginx
mynginx.charts.helm.k8s.io "example-mynginx" deleted
$ ~/junk/my-nginx-operator/deploy/crds $ kubectl get po
NAME                                         READY   STATUS        RESTARTS   AGE
example-mynginx-nginx-app-7dfc477d84-8857k   0/1     Terminating   0          20m
example-mynginx-nginx-app-7dfc477d84-9n5jt   0/1     Terminating   0          20m
example-mynginx-nginx-app-7dfc477d84-z7h48   0/1     Terminating   0          20m
...