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User Guide

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

Prerequisites

  • dep version v0.5.0+.
  • git
  • go version v1.10+.
  • docker version 17.03+.
  • kubectl version v1.9.0+.
  • Access to a kubernetes v.1.9.0+ cluster.

Note: This guide uses minikube version v0.25.0+ as the local kubernetes cluster and quay.io for the public registry.

Install the Operator SDK CLI

The Operator SDK has a CLI tool that helps the developer to create, build, and deploy a new operator project.

Checkout the desired release tag and install the SDK CLI tool:

$ mkdir -p $GOPATH/src/github.com/operator-framework
$ cd $GOPATH/src/github.com/operator-framework
$ git clone https://github.com/operator-framework/operator-sdk
$ cd operator-sdk
$ git checkout master
$ make dep
$ make install

This installs the CLI binary operator-sdk at $GOPATH/bin.

Create a new project

Use the CLI to create a new memcached-operator project:

$ mkdir -p $GOPATH/src/github.com/example-inc/
$ cd $GOPATH/src/github.com/example-inc/
$ operator-sdk new memcached-operator --api-version=cache.example.com/v1alpha1 --kind=Memcached
$ cd memcached-operator

This creates the memcached-operator project specifically for watching the Memcached resource with APIVersion cache.example.com/v1apha1 and Kind Memcached.

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

Customize the operator logic

For this example the memcached-operator will execute the following reconciliation logic for each Memcached CR:

  • Create a memcached Deployment if it doesn't exist
  • Ensure that the Deployment size is the same as specified by the Memcached CR spec
  • Update the Memcached CR status with the names of the memcached pods

Watch the Memcached CR

By default, the memcached-operator watches Memcached resource events as shown in cmd/memcached-operator/main.go.

func main() {
  sdk.Watch("cache.example.com/v1alpha1", "Memcached", "default", time.Duration(5)*time.Second)
  sdk.Handle(stub.NewHandler())
  sdk.Run(context.TODO())
}

Options

Worker Count The number of concurrent informer workers can be configured with an additional Watch option. The default value is 1 if an argument is not given.

sdk.Watch("cache.example.com/v1alpha1", "Memcached", "default", time.Duration(5)*time.Second, sdk.WithNumWorkers(n))

Label Selector Label selectors allow the watch to filter resources by kubernetes labels. It can be specified using the standard kubernetes label selector format:

https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/#label-selectors

sdk.Watch("cache.example.com/v1alpha1", "Memcached", "default", time.Duration(5)*time.Second, sdk.WithLabelSelector("app=myapp"))

Define the Memcached spec and status

Modify the spec and status of the Memcached CR at pkg/apis/cache/v1alpha1/types.go:

type MemcachedSpec struct {
	// Size is the size of the memcached deployment
	Size int32 `json:"size"`
}
type MemcachedStatus struct {
	// Nodes are the names of the memcached pods
	Nodes []string `json:"nodes"`
}

Update the generated code for the CR:

$ operator-sdk generate k8s

Define the Handler

The reconciliation loop for an event is defined in the Handle() function at pkg/stub/handler.go.

Replace the default handler with the reference memcached handler implementation.

Note: The provided handler implementation is only meant to demonstrate the use of the SDK APIs and is not representative of the best practices of a reconciliation loop.

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:

$ kubectl create -f deploy/crd.yaml

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

  • As pod inside Kubernetes cluster
  • As go program outside cluster

1. Run as pod inside a Kubernetes cluster

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

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

$ operator-sdk build quay.io/example/memcached-operator:v0.0.1
$ sed -i 's|REPLACE_IMAGE|quay.io/example/memcached-operator:v0.0.1|g' deploy/operator.yaml
$ docker push quay.io/example/memcached-operator:v0.0.1

Kubernetes deployment manifests are generated in deploy/operator.yaml. The deployment image is set to the container image specified above.

Deploy the memcached-operator:

$ kubectl create -f deploy/sa.yaml
$ kubectl create -f deploy/rbac.yaml
$ kubectl create -f deploy/operator.yaml

Verify that the memcached-operator is up and running:

$ kubectl get deployment
NAME                     DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
memcached-operator       1         1         1            1           1m

2. Run outside the cluster

This method is preferred during development cycle to deploy and test faster.

Run the operator locally with the default kubernetes config file present at $HOME/.kube/config:

$ operator-sdk up local
INFO[0000] Go Version: go1.10
INFO[0000] Go OS/Arch: darwin/amd64
INFO[0000] operator-sdk Version: 0.0.5+git

Run the operator locally with a provided kubernetes config file:

$ operator-sdk up local --kubeconfig=config
INFO[0000] Go Version: go1.10
INFO[0000] Go OS/Arch: darwin/amd64
INFO[0000] operator-sdk Version: 0.0.5+git

Create a Memcached CR

Modify deploy/cr.yaml as shown and create a Memcached custom resource:

$ cat deploy/cr.yaml
apiVersion: "cache.example.com/v1alpha1"
kind: "Memcached"
metadata:
  name: "example-memcached"
spec:
  size: 3

$ kubectl apply -f deploy/cr.yaml

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

$ kubectl get deployment
NAME                     DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
memcached-operator       1         1         1            1           2m
example-memcached        3         3         3            3           1m

Check the pods and CR status to confirm the status is updated with the memcached pod names:

$ kubectl get pods
NAME                                  READY     STATUS    RESTARTS   AGE
example-memcached-6fd7c98d8-7dqdr     1/1       Running   0          1m
example-memcached-6fd7c98d8-g5k7v     1/1       Running   0          1m
example-memcached-6fd7c98d8-m7vn7     1/1       Running   0          1m
memcached-operator-7cc7cfdf86-vvjqk   1/1       Running   0          2m
$ kubectl get memcached/example-memcached -o yaml
apiVersion: cache.example.com/v1alpha1
kind: Memcached
metadata:
  clusterName: ""
  creationTimestamp: 2018-03-31T22:51:08Z
  generation: 0
  name: example-memcached
  namespace: default
  resourceVersion: "245453"
  selfLink: /apis/cache.example.com/v1alpha1/namespaces/default/memcacheds/example-memcached
  uid: 0026cc97-3536-11e8-bd83-0800274106a1
spec:
  size: 3
status:
  nodes:
  - example-memcached-6fd7c98d8-7dqdr
  - example-memcached-6fd7c98d8-g5k7v
  - example-memcached-6fd7c98d8-m7vn7

Update the size

Change the spec.size field in the memcached CR from 3 to 4 and apply the change:

$ cat deploy/cr.yaml
apiVersion: "cache.example.com/v1alpha1"
kind: "Memcached"
metadata:
  name: "example-memcached"
spec:
  size: 4

$ kubectl apply -f deploy/cr.yaml

Confirm that the operator changes the deployment size:

$ kubectl get deployment
NAME                 DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
example-memcached    4         4         4            4           5m

Cleanup

Clean up the resources:

$ kubectl delete -f deploy/cr.yaml
$ kubectl delete -f deploy/operator.yaml

Advanced Topics

Adding 3rd Party Resources To Your Operator

To add a resource to an operator, you must add it to a scheme. By creating an AddToScheme method or reusing one you can easily add a resource to your scheme. An example shows that you define a function and then use the runtime package to create a SchemeBuilder

Current Operator-SDK

You then need to tell the operators to use these functions to add the resources to its scheme. In operator-sdk you use AddToSDKScheme to add this. Example of you main.go:

import (
    ....
    appsv1 "k8s.io/api/apps/v1"
)

func main() {
    k8sutil.AddToSDKScheme(appsv1.AddToScheme)`
    sdk.Watch(appsv1.SchemeGroupVersion.String(), "Deployments", <namespace>, <resyncPeriod>)
}

Future with Controller Runtime

When using controller runtime, you will also need to tell its scheme about your resourece. In controller runtime to add to the scheme, you can get the managers scheme. If you would like to see what kubebuilder generates to add the resoureces to the scheme. Example:

import (
    ....
    appsv1 "k8s.io/api/apps/v1"
)

func main() {
    ....
    if err := appsv1.AddToScheme(mgr.GetScheme()); err != nil {
        log.Fatal(err)
    }
    ....
}