mgr, err := manager.New(cfg, manager.Options{Namespace: namespace})
This guide walks through an example of building a simple Memcached Operator
(memcached-operator) using the operator-sdk CLI tool and
controller-runtime library API. It also shows how to manage the new Operator’s
lifecycle from installation through updating to a new version.
As an administrator of a Kubernetes-based cluster, you can accomplish this using two centerpieces of the Operator Framework:
Assists developers in bootstrapping and building an Operator based on their expertise without requiring knowledge of Kubernetes API complexities.
Helps Operator users install, update, and generally manage the lifecycle of all Operators and their associated services running across their clusters.
The Operator Framework is an open source toolkit to manage Kubernetes native applications, called Operators, in an effective, automated, and scalable way. Operators take advantage of Kubernetes' extensibility to deliver the automation advantages of cloud services like provisioning, scaling, and backup and restore, while being able to run anywhere that Kubernetes can run.
Operators make it easy to manage complex, stateful applications on top of Kubernetes. However, writing an Operator today can be difficult because of challenges such as using low-level APIs, writing boilerplate, and a lack of modularity, which leads to duplication.
The Operator SDK is a framework designed to make writing operators easier by providing:
High-level APIs and abstractions to write the operational logic more intuitively
Tools for scaffolding and code generation to quickly bootstrap a new project
Extensions to cover common operator use cases
The SDK provides the following workflow to develop a new operator:
Create a new Operator project using the SDK command line interface (CLI).
Define new resource APIs by adding Custom Resource Definitions (CRDs).
Specify resources to watch using the SDK API.
Define the Operator reconciling logic in a designated handler and use the SDK API to interact with resources.
Use the SDK CLI to build and generate the Operator deployment manifests.
At a high level, an Operator using the SDK processes events for watched resources in a user-defined handler and takes actions to reconcile the state of the application.
The main program for the Operator is the manager cmd/manager/main.go file. The
manager automatically registers the scheme for all custom resources defined
under pkg/apis/ and runs all controllers under pkg/controller/.
The manager can restrict the namespace that all controllers watch for resources:
mgr, err := manager.New(cfg, manager.Options{Namespace: namespace})
By default, this is the namespace that the Operator is running in. To watch all namespaces, you can leave the namespace option empty:
mgr, err := manager.New(cfg, manager.Options{Namespace: ""})
The Operator SDK has a CLI tool that assists developers in creating, building, and deploying a new Operator project. You can install the SDK CLI on your workstation so you are prepared to start authoring your own Operators.
Clone an operator-sdk repository:
$ 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
Check out the desired release branch:
$ git checkout master
Install the SDK CLI tool:
$ make dep $ make install
This installs the CLI binary operator-sdk at $GOPATH/bin.
Verify that the CLI tool was installed correctly:
$ operator-sdk -h
The Operator SDK makes it easier to build Kubernetes native applications, a process that can require deep, application-specific operational knowledge. The SDK not only lowers that barrier, but it also helps reduce the amount of boilerplate code needed for many common management capabilities, such as metering or monitoring.
This procedure walks through an example of building a simple Memcached Operator using tools and libraries provided by the SDK.
Operator SDK CLI installed on the development workstation
Operator Lifecycle Manager (OLM) installed on a Kubernetes-based cluster (v1.8
or above to support the apps/v1beta2 API group), for example OKD 4.0
Access to the cluster using an account with cluster-admin permissions
kubectl v1.11.3+
(can alternatively use oc)
Create a new project.
Use the CLI to create a new memcached-operator project:
$ cd $GOPATH/src/github.com/example-inc/ $ operator-sdk new memcached-operator $ cd memcached-operator
|
See Appendices to learn about the project directory structure created by the previous commands. |
Add a new Custom Resource Definition (CRD).
Use the CLI to add a new CRD API called Memcached, with APIVersion set to
cache.example.com/v1apha1 and Kind set to Memcached:
$ operator-sdk add api \
--api-version=cache.example.com/v1alpha1 \
--kind=Memcached
This scaffolds the Memcached resource API under pkg/apis/cache/v1alpha1/.
Modify the spec and status of the Memcached Custom Resource (CR) at the
pkg/apis/cache/v1alpha1/memcached_types.go file:
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"`
}
After modifying the *_types.go file, always run the following command to
update the generated code for that resource type:
$ operator-sdk generate k8s
Add a new Controller.
Add a new Controller to the project to watch and reconcile the Memcached resource:
$ operator-sdk add controller \
--api-version=cache.example.com/v1alpha1 \
--kind=Memcached
This scaffolds a new Controller implementation under
pkg/controller/memcached/.
For this example, replace the generated controller file
pkg/controller/memcached/memcached_controller.go with the
example implementation.
The example controller executes the following reconciliation logic for each
Memcached CR:
Create a Memcached Deployment if it does not 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.
The next two sub-steps inspect how the Controller watches resources and how the reconcile loop is triggered. You can skip skip these steps step to go directly to building and running the Operator.
Inspect the Controller implementation at the
pkg/controller/memcached/memcached_controller.go file to see how the
Controller watches resources.
The first watch is for the Memcached type as the primary resource. For each Add,
Update, or Delete event, the reconcile loop is sent a reconcile Request (a
<namespace>:<name> key) for that Memcached object:
err := c.Watch(
&source.Kind{Type: &cachev1alpha1.Memcached{}}, &handler.EnqueueRequestForObject{})
The next watch is for Deployments, but the event handler maps each event to a
reconcile Request for the owner of the Deployment. In this case, this is the
Memcached object for which the Deployment was created. This allows the
controller to watch Deployments as a secondary resource:
err := c.Watch(&source.Kind{Type: &appsv1.Deployment{}}, &handler.EnqueueRequestForOwner{
IsController: true,
OwnerType: &cachev1alpha1.Memcached{},
})
Every Controller has a Reconciler object with a Reconcile() method that
implements the reconcile loop. The reconcile loop is passed the Request
argument which is a <namespace>:<name> key used to lookup the primary resource
object, Memcached, from the cache:
func (r *ReconcileMemcached) Reconcile(request reconcile.Request) (reconcile.Result, error) {
// Lookup the Memcached instance for this reconcile request
memcached := &cachev1alpha1.Memcached{}
err := r.client.Get(context.TODO(), request.NamespacedName, memcached)
...
}
Based on the return value of Reconcile() the reconcile Request may be
requeued and the loop may be triggered again:
// Reconcile successful - don't requeue
return reconcile.Result{}, nil
// Reconcile failed due to error - requeue
return reconcile.Result{}, err
// Requeue for any reason other than error
return reconcile.Result{Requeue: true}, nil
Build and run the Operator.
Before running the Operator, the CRD must be registered with the Kubernetes API server:
$ kubectl create \
-f deploy/crds/cache_v1alpha1_memcached_crd.yaml
After registering the CRD, there are two options for running the Operator:
As a Deployment inside a Kubernetes cluster
As Go program outside a cluster
Choose one of the following methods.
Option A: Running as a Deployment inside the cluster.
Build the memcached-operator image and push it to a registry:
$ operator-sdk build quay.io/example/memcached-operator:v0.0.1
The Deployment manifest is generated at deploy/operator.yaml. Update the
Deployment image as follows since the default is just a placeholder:
$ sed -i 's|REPLACE_IMAGE|quay.io/example/memcached-operator:v0.0.1|g' deploy/operator.yaml
Ensure you have an account on quay.io for the next step,
or substitute your preferred container registry. On the registry,
create a new public image repository named
memcached-operator.
Push the image to the registry:
$ docker push quay.io/example/memcached-operator:v0.0.1
Setup RBAC and deploy memcached-operator:
$ kubectl create -f deploy/role.yaml $ kubectl create -f deploy/role_binding.yaml # TODO: $ kubectl create -f deploy/service_account.yaml $ kubectl create -f deploy/operator.yaml
Verify that memcached-operator is up and running:
$ kubectl get deployment NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE memcached-operator 1 1 1 1 1m
Option B: Running locally outside the cluster.
This method is preferred during development cycle to deploy and test faster.
Run the Operator locally with the default Kubernetes configuration file present
at $HOME/.kube/config:
$ operator-sdk up local --namespace=default 2018/09/30 23:10:11 Go Version: go1.10.2 2018/09/30 23:10:11 Go OS/Arch: darwin/amd64 2018/09/30 23:10:11 operator-sdk Version: 0.0.6+git 2018/09/30 23:10:12 Registering Components. 2018/09/30 23:10:12 Starting the Cmd.
You can use a specific kubeconfig using the flag
--kubeconfig=<path/to/kubeconfig>.
Verify that the Operator can deploy a Memcached application by creating a Memcached CR.
Create the example Memcached CR that was generated at
deploy/crds/cache_v1alpha1_memcached_cr.yaml:
$ cat deploy/crds/cache_v1alpha1_memcached_cr.yaml apiVersion: "cache.example.com/v1alpha1" kind: "Memcached" metadata: name: "example-memcached" spec: size: 3 $ kubectl apply -f deploy/crds/cache_v1alpha1_memcached_cr.yaml
Ensure that 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
Verify that the Operator can manage a deployed Memcached application by updating the size of the deployment.
Change the spec.size field in the memcached CR from 3 to 4:
$ cat deploy/crds/cache_v1alpha1_memcached_cr.yaml apiVersion: "cache.example.com/v1alpha1" kind: "Memcached" metadata: name: "example-memcached" spec: size: 4
Apply the change:
$ kubectl apply -f deploy/crds/cache_v1alpha1_memcached_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
Clean up the resources:
$ kubectl delete -f deploy/crds/cache_v1alpha1_memcached_cr.yaml $ kubectl delete -f deploy/operator.yaml
The previous section has covered manually running an Operator. In the next sections, we will explore using the Operator Lifecycle Manager (OLM), which is what enables a more robust deployment model for Operators being run in production environments.
The OLM helps you to install, update, and generally manage the lifecycle of all
of the Operators (and their associated services) on a Kubernetes cluster. It
runs as an Kubernetes extension and lets you use kubectl for all the lifecycle
management functions without any additional tools.
OLM installed on a Kubernetes-based cluster (v1.8 or above to support the
apps/v1beta2 API group), for example OKD 4.0
Preview OLM enabled
Memcached Operator built
Generate an Operator manifest.
An Operator manifest describes how to display, create, and manage the
application, in this case Memcached, as a whole. It is defined by a
CustomServiceVersion (CSV) object and is required for the OLM to function.
For the purpose of this guide, we will continue with this predefined manifest file for the next steps. You can alter the image field within this manifest to reflect the image you built in previous steps, but it is unnecessary. In the future, the Operator SDK CLI will generate an Operator manifest for you, a feature that is planned for the next release of the Operator SDK.
|
See Building a CSV for the Operator Framework for more information on manually defining a manifest file. |
Deploy the Operator.
Deploy an Operator by applying the Operator’s manifest to the desired namespace in the cluster:
$ curl -Lo memcachedoperator.0.0.1.csv.yaml https://raw.githubusercontent.com/operator-framework/getting-started/master/memcachedoperator.0.0.1.csv.yaml $ kubectl apply -f memcachedoperator.0.0.1.csv.yaml $ kubectl get ClusterServiceVersion memcachedoperator.v0.0.1 -o json | jq '.status'
After applying this manifest, nothing has happened yet, because the cluster does
not meet the requirements specified in our manifest. Create the RBAC rules and
CustomResourceDefinition for the Memcached type managed by the Operator:
$ kubectl apply -f deploy/rbac.yaml $ kubectl apply -f deploy/crd.yaml
Because the OLM creates Operators in a particular namespace when a manifest is applied, administrators can leverage the native Kubernetes RBAC permission model to restrict which users are allowed to install Operators.
Create an application instance.
The Memcached Operator is now running in the memcached namespace. Users
interact with Operators via instances of CustomResources; in this case, the
resource has the kind Memcached. Native Kubernetes RBAC also applies to
CustomResources, providing administrators control over who can interact with
each Operator.
Creating instances of Memcached in this namespace will now trigger the Memcached
Operator to instantiate pods running the memcached server that are managed by
the Operator. The more CustomResources you create, the more unique instances
of Memcached are managed by the Memcached Operator running in this namespace.
$ cat <<EOF | kubectl apply -f - apiVersion: "cache.example.com/v1alpha1" kind: "Memcached" metadata: name: "memcached-for-wordpress" spec: size: 1 EOF $ cat <<EOF | kubectl apply -f - apiVersion: "cache.example.com/v1alpha1" kind: "Memcached" metadata: name: "memcached-for-drupal" spec: size: 1 EOF $ kubectl get Memcached NAME AGE memcached-for-drupal 22s memcached-for-wordpress 27s $ kubectl get pods NAME READY STATUS RESTARTS AGE memcached-app-operator-66b5777b79-pnsfj 1/1 Running 0 14m memcached-for-drupal-5476487c46-qbd66 1/1 Running 0 3s memcached-for-wordpress-65b75fd8c9-7b9x7 1/1 Running 0 8s
Update an application.
Manually apply an update to the Operator by creating a new Operator manifest
with a replaces field that references the old Operator manifest. The OLM
ensures that all resources being managed by the old Operator have their
ownership moved to the new Operator without fear of any programs stopping
execution. It is up to the Operators themselves to execute any data migrations
required to upgrade resources to run under a new version of the Operator.
The following command demonstrates applying a new Operator manifest file using a new version of the Operator and shows that the pods remain executing:
$ curl -Lo memcachedoperator.0.0.2.csv.yaml https://raw.githubusercontent.com/operator-framework/getting-started/master/memcachedoperator.0.0.2.csv.yaml $ kubectl apply -f memcachedoperator.0.0.2.csv.yaml $ kubectl get pods NAME READY STATUS RESTARTS AGE memcached-app-operator-66b5777b79-pnsfj 1/1 Running 0 3s memcached-for-drupal-5476487c46-qbd66 1/1 Running 0 14m memcached-for-wordpress-65b75fd8c9-7b9x7 1/1 Running 0 14m
This guide provides an effective demonstration of the value of the Operator Framework for building and managing Operators, but this is much more left out in the interest of brevity. The Operator Framework and its components are open source, so visit each project individually and learn what else you can do:
If you want to discuss your experience, have questions, or want to get involved, join the Operator Framework mailing list.