Operator developers can take advantage of Ansible support in the Operator SDK to build an example Ansible-based Operator for Memcached, a distributed key-value store, and manage its lifecycle. This tutorial walks through the following process:

  • Create a Memcached deployment

  • Ensure that the deployment size is the same as specified by the Memcached custom resource (CR) spec

  • Update the Memcached CR status using the status writer with the names of the memcached pods

This process is accomplished by using two centerpieces of the Operator Framework:

Operator SDK

The operator-sdk CLI tool and controller-runtime library API

Operator Lifecycle Manager (OLM)

Installation, upgrade, and role-based access control (RBAC) of Operators on a cluster

This tutorial goes into greater detail than Getting started with Operator SDK for Ansible-based Operators.

Prerequisites

Creating a project

Use the Operator SDK CLI to create a project called memcached-operator.

Procedure
  1. Create a directory for the project:

    $ mkdir -p $HOME/projects/memcached-operator
  2. Change to the directory:

    $ cd $HOME/projects/memcached-operator
  3. Run the operator-sdk init command with the ansible plug-in to initialize the project:

    $ operator-sdk init \
        --plugins=ansible \
        --domain=example.com

PROJECT file

Among the files generated by the operator-sdk init command is a Kubebuilder PROJECT file. Subsequent operator-sdk commands, as well as help output, that are run from the project root read this file and are aware that the project type is Ansible. For example:

domain: example.com
layout: ansible.sdk.operatorframework.io/v1
projectName: memcached-operator
version: 3-alpha

Creating an API

Use the Operator SDK CLI to create a Memcached API.

Procedure
  • Run the following command to create an API with group cache, version, v1, and kind Memcached:

    $ operator-sdk create api \
        --group cache \
        --version v1 \
        --kind Memcached \
        --generate-role (1)
    1 Generates an Ansible role for the API.

After creating the API, your Operator project updates with the following structure:

Memcached CRD

Includes a sample Memcached resource

Manager

Program that reconciles the state of the cluster to the desired state by using:

  • A reconciler, either an Ansible role or playbook

  • A watches.yaml file, which connects the Memcached resource to the memcached Ansible role

Modifying the manager

Update your Operator project to provide the reconcile logic, in the form of an Ansible role, which runs every time a Memcached resource is created, updated, or deleted.

Procedure
  1. Update the roles/memcached/tasks/main.yml file with the following structure:

    ---
    - name: start memcached
      community.kubernetes.k8s:
        definition:
          kind: Deployment
          apiVersion: apps/v1
          metadata:
            name: '{{ ansible_operator_meta.name }}-memcached'
            namespace: '{{ ansible_operator_meta.namespace }}'
          spec:
            replicas: "{{size}}"
            selector:
              matchLabels:
                app: memcached
            template:
              metadata:
                labels:
                  app: memcached
              spec:
                containers:
                - name: memcached
                  command:
                  - memcached
                  - -m=64
                  - -o
                  - modern
                  - -v
                  image: "docker.io/memcached:1.4.36-alpine"
                  ports:
                    - containerPort: 11211

    This memcached role ensures a memcached deployment exist and sets the deployment size.

  2. Set default values for variables used in your Ansible role by editing the roles/memcached/defaults/main.yml file:

    ---
    # defaults file for Memcached
    size: 1
  3. Update the Memcached sample resource in the config/samples/cache_v1_memcached.yaml file with the following structure:

    apiVersion: cache.example.com/v1
    kind: Memcached
    metadata:
      name: memcached-sample
    spec:
      size: 3

    The key-value pairs in the custom resource (CR) spec are passed to Ansible as extra variables.

The names of all variables in the spec field are converted to snake case, meaning lowercase with an underscore, by the Operator before running Ansible. For example, serviceAccount in the spec becomes service_account in Ansible.

You can disable this case conversion by setting the snakeCaseParameters option to false in your watches.yaml file. It is recommended that you perform some type validation in Ansible on the variables to ensure that your application is receiving expected input.

Running the Operator

There are three ways you can use the Operator SDK CLI to build and run your Operator:

  • Run locally outside the cluster as a Go program.

  • Run as a deployment on the cluster.

  • Bundle your Operator and use Operator Lifecycle Manager (OLM) to deploy on the cluster.

Running locally outside the cluster

You can run your Operator project as a Go program outside of the cluster. This is useful for development purposes to speed up deployment and testing.

Procedure
  • Run the following command to install the custom resource definitions (CRDs) in the cluster configured in your ~/.kube/config file and run the Operator locally:

    $ make install run
    Example output
    ...
    {"level":"info","ts":1612589622.7888272,"logger":"ansible-controller","msg":"Watching resource","Options.Group":"cache.example.com","Options.Version":"v1","Options.Kind":"Memcached"}
    {"level":"info","ts":1612589622.7897573,"logger":"proxy","msg":"Starting to serve","Address":"127.0.0.1:8888"}
    {"level":"info","ts":1612589622.789971,"logger":"controller-runtime.manager","msg":"starting metrics server","path":"/metrics"}
    {"level":"info","ts":1612589622.7899997,"logger":"controller-runtime.manager.controller.memcached-controller","msg":"Starting EventSource","source":"kind source: cache.example.com/v1, Kind=Memcached"}
    {"level":"info","ts":1612589622.8904517,"logger":"controller-runtime.manager.controller.memcached-controller","msg":"Starting Controller"}
    {"level":"info","ts":1612589622.8905244,"logger":"controller-runtime.manager.controller.memcached-controller","msg":"Starting workers","worker count":8}

Running as a deployment on the cluster

You can run your Operator project as a deployment on your cluster.

Procedure
  1. Run the following make commands to build and push the Operator image. Modify the IMG argument in the following steps to reference a repository that you have access to. You can obtain an account for storing containers at repository sites such as Quay.io.

    1. Build the image:

      $ make docker-build IMG=<registry>/<user>/<image_name>:<tag>
    2. Push the image to a repository:

      $ make docker-push IMG=<registry>/<user>/<image_name>:<tag>

      The name and tag of the image, for example IMG=<registry>/<user>/<image_name>:<tag>, in both the commands can also be set in your Makefile. Modify the IMG ?= controller:latest value to set your default image name.

  2. Run the following command to deploy the Operator:

    $ make deploy IMG=<registry>/<user>/<image_name>:<tag>

    By default, this command creates a namespace with the name of your Operator project in the form <project_name>-system and is used for the deployment. This command also installs the RBAC manifests from config/rbac.

  3. Verify that the Operator is running:

    $ oc get deployment -n <project_name>-system
    Example output
    NAME                                    READY   UP-TO-DATE   AVAILABLE   AGE
    <project_name>-controller-manager       1/1     1            1           8m

Bundling an Operator and deploying with Operator Lifecycle Manager

Bundling an Operator

The Operator bundle format is the default packaging method for Operator SDK and Operator Lifecycle Manager (OLM). You can get your Operator ready for use on OLM by using the Operator SDK to build and push your Operator project as a bundle image.

Prerequisites
  • Operator SDK CLI installed on a development workstation

  • OpenShift CLI (oc) v4.8+ installed

  • Operator project initialized by using the Operator SDK

Procedure
  1. Run the following make commands in your Operator project directory to build and push your Operator image. Modify the IMG argument in the following steps to reference a repository that you have access to. You can obtain an account for storing containers at repository sites such as Quay.io.

    1. Build the image:

      $ make docker-build IMG=<registry>/<user>/<operator_image_name>:<tag>
    2. Push the image to a repository:

      $ make docker-push IMG=<registry>/<user>/<operator_image_name>:<tag>
  2. Update your Makefile by setting the IMG URL to your Operator image name and tag that you pushed:

    $ # Image URL to use all building/pushing image targets
    IMG ?= <registry>/<user>/<operator_image_name>:<tag>

    This value is used for subsequent operations.

  3. Create your Operator bundle manifest by running the make bundle command, which invokes several commands, including the Operator SDK generate bundle and bundle validate subcommands:

    $ make bundle

    Bundle manifests for an Operator describe how to display, create, and manage an application. The make bundle command creates the following files and directories in your Operator project:

    • A bundle manifests directory named bundle/manifests that contains a ClusterServiceVersion object

    • A bundle metadata directory named bundle/metadata

    • All custom resource definitions (CRDs) in a config/crd directory

    • A Dockerfile bundle.Dockerfile

    These files are then automatically validated by using operator-sdk bundle validate to ensure the on-disk bundle representation is correct.

  4. Build and push your bundle image by running the following commands. OLM consumes Operator bundles using an index image, which reference one or more bundle images.

    1. Build the bundle image. Set BUNDLE_IMG with the details for the registry, user namespace, and image tag where you intend to push the image:

      $ make bundle-build BUNDLE_IMG=<registry>/<user>/<bundle_image_name>:<tag>
    2. Push the bundle image:

      $ docker push <registry>/<user>/<bundle_image_name>:<tag>

Deploying an Operator with Operator Lifecycle Manager

Operator Lifecycle Manager (OLM) helps you to install, update, and manage the lifecycle of Operators and their associated services on a Kubernetes cluster. OLM is installed by default on OKD and runs as a Kubernetes extension so that you can use the web console and the OpenShift CLI (oc) for all Operator lifecycle management functions without any additional tools.

The Operator bundle format is the default packaging method for Operator SDK and OLM. You can use the Operator SDK to quickly run a bundle image on OLM to ensure that it runs properly.

Prerequisites
  • Operator SDK CLI installed on a development workstation

  • Operator bundle image built and pushed to a registry

  • OLM installed on a Kubernetes-based cluster (v1.16.0 or later if you use apiextensions.k8s.io/v1 CRDs, for example OKD 4.8)

  • Logged in to the cluster with oc using an account with cluster-admin permissions

Procedure
  1. Check the status of OLM on your cluster by using the following Operator SDK command:

    $ operator-sdk olm status \
        --olm-namespace=openshift-operator-lifecycle-manager
  2. Run the Operator on your cluster by using the OLM integration in Operator SDK:

    $ operator-sdk run bundle \
        [-n <namespace>] \(1)
        <registry>/<user>/<bundle_image_name>:<tag>
    1 By default, the command installs the Operator in the currently active project in your ~/.kube/config file. You can add the -n flag to set a different namespace scope for the installation.

    This command performs the following actions:

    • Create an index image referencing your bundle image. The index image is opaque and ephemeral, but accurately reflects how a bundle would be added to a catalog in production.

    • Create a catalog source that points to your new index image, which enables OperatorHub to discover your Operator.

    • Deploy your Operator to your cluster by creating an OperatorGroup, Subscription, InstallPlan, and all other required objects, including RBAC.

Creating a custom resource

After your Operator is installed, you can test it by creating a custom resource (CR) that is now provided on the cluster by the Operator.

Prerequisites
  • Example Memcached Operator, which provides the Memcached CR, installed on a cluster

Procedure
  1. Change to the namespace where your Operator is installed. For example, if you deployed the Operator using the make deploy command:

    $ oc project memcached-operator-system
  2. Edit the sample Memcached CR manifest at config/samples/cache_v1_memcached.yaml to contain the following specification:

    apiVersion: cache.example.com/v1
    kind: Memcached
    metadata:
      name: memcached-sample
    ...
    spec:
    ...
      size: 3
  3. Create the CR:

    $ oc apply -f config/samples/cache_v1_memcached.yaml
  4. Ensure that the Memcached Operator creates the deployment for the sample CR with the correct size:

    $ oc get deployments
    Example output
    NAME                                    READY   UP-TO-DATE   AVAILABLE   AGE
    memcached-operator-controller-manager   1/1     1            1           8m
    memcached-sample                        3/3     3            3           1m
  5. Check the pods and CR status to confirm the status is updated with the Memcached pod names.

    1. Check the pods:

      $ oc get pods
      Example output
      NAME                                  READY     STATUS    RESTARTS   AGE
      memcached-sample-6fd7c98d8-7dqdr      1/1       Running   0          1m
      memcached-sample-6fd7c98d8-g5k7v      1/1       Running   0          1m
      memcached-sample-6fd7c98d8-m7vn7      1/1       Running   0          1m
    2. Check the CR status:

      $ oc get memcached/memcached-sample -o yaml
      Example output
      apiVersion: cache.example.com/v1
      kind: Memcached
      metadata:
      ...
        name: memcached-sample
      ...
      spec:
        size: 3
      status:
        nodes:
        - memcached-sample-6fd7c98d8-7dqdr
        - memcached-sample-6fd7c98d8-g5k7v
        - memcached-sample-6fd7c98d8-m7vn7
  6. Update the deployment size.

    1. Update config/samples/cache_v1_memcached.yaml file to change the spec.size field in the Memcached CR from 3 to 5:

      $ oc patch memcached memcached-sample \
          -p '{"spec":{"size": 5}}' \
          --type=merge
    2. Confirm that the Operator changes the deployment size:

      $ oc get deployments
      Example output
      NAME                                    READY   UP-TO-DATE   AVAILABLE   AGE
      memcached-operator-controller-manager   1/1     1            1           10m
      memcached-sample                        5/5     5            5           3m
  7. Clean up the resources that have been created as part of this tutorial.

    • If you used the make deploy command to test the Operator, run the following command:

      $ make undeploy
    • If you used the operator-sdk run bundle command to test the Operator, run the following command:

      $ operator-sdk cleanup <project_name>

Additional resources