Tutorial for Helm-based Operators

An in-depth walkthough that demonstrates how to build and run a Helm-based operator.

Overview

This guide walks through an example of building a simple nginx-operator powered by Helm using tools and libraries provided by the Operator SDK.

Prerequisites

  • Install operator-sdk and its prequisites.
  • Access to a Kubernetes v1.16.0+ cluster.
  • User authorized with cluster-admin permissions.

Create a new project

Use the CLI to create a new Helm-based nginx-operator project:

mkdir nginx-operator
cd nginx-operator
operator-sdk init --plugins=helm --domain=com --group=example --version=v1alpha1 --kind=Nginx

This creates the nginx-operator project specifically for watching the Nginx resource with APIVersion example.com/v1alpha1 and Kind Nginx.

For Helm-based projects, operator-sdk init also generates the RBAC rules in config/rbac/role.yaml based on the resources that would be deployed by the chart’s default manifest. Be sure to double check that the rules generated in config/rbac/role.yaml meet the operator’s permission requirements.

To learn more about the project directory structure, see the project layout doc.

Use an existing chart

Instead of creating your project with a boilerplate Helm chart, you can also use --helm-chart, --helm-chart-repo, and --helm-chart-version to use an existing chart, either from your local filesystem or a remote chart repository.

If --helm-chart is specified, the --group, --version, and --kind flags become optional. If left unset, the default will be:

Flag Value
domain my.domain
group charts
kind deduce from the specified chart
version v1alpha1

If --helm-chart is a local chart archive (e.g example-chart-1.2.0.tgz) or directory, it will be validated and unpacked or copied into the project.

Otherwise, the SDK will attempt to fetch the specified helm chart from a remote repository.

If a custom repository URL is not specified by --helm-chart-repo, the following chart reference formats are supported:

  • <repoName>/<chartName>: Fetch the helm chart named chartName from the helm chart repository named repoName, as specified in the $HELM_HOME/repositories/repositories.yaml file. Use helm repo add to configure this file.

  • <url>: Fetch the helm chart archive at the specified URL.

If a custom repository URL is specified by --helm-chart-repo, the only supported format for --helm-chart is:

  • <chartName>: Fetch the helm chart named chartName in the helm chart repository specified by the --helm-chart-repo URL.

If --helm-chart-version is not set, the SDK will fetch the latest available version of the helm chart. Otherwise, it will fetch the specified version. The option --helm-chart-version is not used when --helm-chart itself refers to a specific version, for example when it is a local path or a URL.

Note: For more details and examples run operator-sdk init --plugins=helm --help.

Operator scope

Read the operator scope documentation on how to run your operator as namespace-scoped vs cluster-scoped.

Customize the operator logic

For this example the nginx-operator will execute the following reconciliation logic for each Nginx Custom Resource (CR):

  • Create a nginx Deployment if it doesn’t exist
  • Create a nginx Service if it doesn’t exist
  • Create a nginx Ingress if it is enabled and doesn’t exist
  • Ensure that the Deployment, Service, and optional Ingress match the desired configuration (e.g. replica count, image, service type, etc) as specified by the Nginx CR

Watch the Nginx CR

By default, the nginx-operator watches Nginx resource events as shown in watches.yaml and executes Helm releases using the specified chart:

# Use the 'create api' subcommand to add watches to this file.
- group: example.com
  version: v1alpha1
  kind: Nginx
  chart: helm-charts/nginx
# +kubebuilder:scaffold:watch

Reviewing the Nginx Helm Chart

When a Helm operator project is created, the SDK creates an example Helm chart that contains a set of templates for a simple Nginx release.

For this example, we have templates for deployment, service, and ingress resources, along with a NOTES.txt template, which Helm chart developers use to convey helpful information about a release.

If you aren’t already familiar with Helm Charts, take a moment to review the Helm Chart developer documentation.

Understanding the Nginx CR spec

Helm uses a concept called values to provide customizations to a Helm chart’s defaults, which are defined in the Helm chart’s values.yaml file.

Overriding these defaults is as simple as setting the desired values in the CR spec. Let’s use the number of replicas as an example.

First, inspecting helm-charts/nginx/values.yaml, we see that the chart has a value called replicaCount and it is set to 1 by default. If we want to have 2 nginx instances in our deployment, we would need to make sure our CR spec contained replicaCount: 2.

Update config/samples/example_v1alpha1_nginx.yaml to look like the following:

apiVersion: example.com/v1alpha1
kind: Nginx
metadata:
  name: nginx-sample
spec:
  replicaCount: 2

Similarly, we see that the default service port is set to 80, but we would like to use 8080, so we’ll again update config/samples/example_v1alpha1_nginx.yaml by adding the service port override:

apiVersion: example.com/v1alpha1
kind: Nginx
metadata:
  name: nginx-sample
spec:
  replicaCount: 2
  service:
    port: 8080

As you may have noticed, the Helm operator simply applies the entire spec as if it was the contents of a values file, just like helm install -f ./overrides.yaml works.

Build and run the operator

Before running the operator, Kubernetes needs to know about the new custom resource definition the operator will be watching.

Deploy the CRD:

make install

Once this is done, there are two ways to run the operator:

  • As a pod inside a Kubernetes cluster
  • As a go program outside the cluster using operator-sdk

1. Run as a pod inside a Kubernetes cluster

Running as a pod inside a Kubernetes cluster is preferred for production use.

Build the nginx-operator image and push it to a registry:

export IMG=quay.io/example/nginx-operator:v0.0.1
make docker-build docker-push IMG=$IMG

Note: Kubernetes deployment manifests are generated in config/manager/manager.yaml.

Deploy the nginx-operator:

make deploy IMG=$IMG

Verify that the nginx-operator is up and running:

$ kubectl get deployment -n nginx-operator-system
NAME                                DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
nginx-operator-controller-manager   1/1       1         1            1           77s

2. Run outside the cluster

This method is preferred during the development cycle to speed up deployment and testing.

Run the operator locally with the default Kubernetes config file present at $HOME/.kube/config via the Makefile target make run.

3. Deploy your Operator with the Operator Lifecycle Manager (OLM)

OLM will manage creation of most if not all resources required to run your operator, using a bit of setup from other operator-sdk commands. Check out the OLM integration [user guide][quickstart-bundle] for more information.

Deploy the Nginx custom resource

Apply the nginx CR that we modified earlier:

kubectl apply -f config/samples/example_v1alpha1_nginx.yaml

Ensure that the nginx-operator creates the deployment for the CR:

$ kubectl get deployment
NAME           READY   UP-TO-DATE   AVAILABLE   AGE
nginx-sample   2/2     2            2           2m13s

Check the pods to confirm 2 replicas were created:

$ kubectl get pods
NAME                                                   READY   STATUS    RESTARTS   AGE
nginx-sample-c786bfdcf-4g6md                           1/1     Running   0          81s
nginx-sample-c786bfdcf-6bhmx                           1/1     Running   0          81s

Check that the service port is set to `8080`:

```sh
$ kubectl get service
NAME                                      TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
nginx-sample                              ClusterIP   10.96.26.3   <none>        8080/TCP   1m

Update the replicaCount and remove the port

Change the spec.replicaCount field from 2 to 3, remove the spec.service field:

$ cat config/samples/example_v1alpha1_nginx.yaml
apiVersion: example.com/v1alpha1
kind: Nginx
metadata:
  name: nginx-sample
spec:
  replicaCount: 3

And apply the change:

kubectl apply -f config/samples/example_v1alpha1_nginx.yaml

Confirm that the operator changes the deployment size:

$ kubectl get deployment
NAME                                           DESIRED   CURRENT   UP-TO-DATE     AGE
nginx-sample                                   3/3       3            3           7m29s

Check that the service port is set to the default (80):

$ kubectl get service
NAME                                      TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)  AGE
nginx-sample                              ClusterIP   10.96.152.76    <none>        80/TCP   7m54s

Troubleshooting

Use the following command to check the operator logs.

kubectl logs deployment.apps/nginx-operator-controller-manager  -n nginx-operator-system -c manager

Use the following command to check the CR status and events.

kubectl describe nginxes.example.com 

Cleanup

Clean up the resources:

kubectl delete -f config/samples/example_v1alpha1_nginx.yaml
make undeploy

NOTE Additional CR/CRD’s can be added to the project by running, for example, the command :operator-sdk create api --group=example --version=v1alpha1 --kind=AppService