Tutorial for Helm-based Operators
This guide walks through an example of building a simple nginx-operator powered by Helm using tools and libraries provided by the Operator SDK.
operator-sdkand its prequisites.
- Access to a Kubernetes v1.16.0+ cluster.
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
For Helm-based projects,
operator-sdk init also generates the RBAC rules
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
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-version to use an existing chart, either from your local filesystem or a remote chart repository.
--helm-chart is specified, the
--kind flags become optional. If left unset, the default will be:
|kind||deduce from the specified chart|
--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
chartNamefrom the helm chart repository named
repoName, as specified in the
helm repo addto 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
<chartName>: Fetch the helm chart named
chartNamein the helm chart repository specified by the
--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.
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
Watch the Nginx CR
By default, the nginx-operator watches
Nginx resource events as shown
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
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.
helm-charts/nginx/values.yaml, we see that the chart has a
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
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
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
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:
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
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=$IMG
Note: Kubernetes deployment manifests are generated in
Deploy the nginx-operator:
make deploy IMG=$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
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
spec.replicaCount field from 2 to 3, remove the
$ 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 (
$ kubectl get service NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE nginx-sample ClusterIP 10.96.152.76 <none> 80/TCP 7m54s
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
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