Ansible Operator Tutorial

An in-depth walkthough of building and running an Ansible-based operator.

NOTE: If your project was created with an operator-sdk version prior to v1.0.0 please migrate, or consult the legacy docs.

Prerequisites

Overview

We will create a sample project to let you know how it works and this sample will:

  • 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 using the status writer with the names of the memcached pods

Create a new project

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

  1. $ mkdir memcached-operator
  2. $ cd memcached-operator
  3. $ operator-sdk init --plugins=ansible --domain example.com

Among the files generated by this command is a Kubebuilder PROJECT file. Subsequent operator-sdk commands (and help text) run from the project root read this file and are aware that the project type is Ansible.

  1. # Since this is an Ansible-based project, this help text is Ansible specific.
  2. $ operator-sdk create api -h

Next, we will create a Memcached API.

  1. $ operator-sdk create api --group cache --version v1alpha1 --kind Memcached --generate-role

The scaffolded operator has the following structure:

  • Memcached Custom Resource Definition, and a sample Memcached resource.
  • A “Manager” that reconciles the state of the cluster to the desired state
    • A reconciler, which is an Ansible Role or Playbook.
    • A watches.yaml file, which connects the Memcached resource to the memcached Ansible Role.

See scaffolded files reference and watches reference for more detailed information

Modify the Manager

Now we need to provide the reconcile logic, in the form of an Ansible Role, which will run every time a Memcached resource is created, updated, or deleted.

Update roles/memcached/tasks/main.yml:

  1. ---
  2. - name: start memcached
  3.   community.kubernetes.k8s:
  4.     definition:
  5.       kind: Deployment
  6.       apiVersion: apps/v1
  7.       metadata:
  8.         name: '{{ ansible_operator_meta.name }}-memcached'
  9.         namespace: '{{ ansible_operator_meta.namespace }}'
  10.       spec:
  11.         replicas: "{{size}}"
  12.         selector:
  13.           matchLabels:
  14.             app: memcached
  15.         template:
  16.           metadata:
  17.             labels:
  18.               app: memcached
  19.           spec:
  20.             containers:
  21.             - name: memcached
  22.               command:
  23.               - memcached
  24.               - -m=64
  25.               - -o
  26.               - modern
  27.               - -v
  28.               image: "docker.io/memcached:1.4.36-alpine"
  29.               ports:
  30.                 - containerPort: 11211

This memcached role will:

  • Ensure a memcached Deployment exists
  • Set the Deployment size

It is good practice to set default values for variables used in Ansible Roles, so edit roles/memcached/defaults/main.yml:

  1. ---
  2. # defaults file for Memcached
  3. size: 1

Finally, update the Memcached sample, config/samples/cache_v1alpha1_memcached.yaml:

  1. apiVersion: cache.example.com/v1alpha1
  2. kind: Memcached
  3. metadata:
  4.   name: memcached-sample
  5. spec:
  6.   size: 3

The key-value pairs in the Custom Resource spec are passed to Ansible as extra variables.

Note: The names of all variables in the spec field are converted to snake_case 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. It is recommended that you perform some type validation in Ansible on the variables to ensure that your application is receiving expected input.

Finishing up

All that remains is building and pushing the operator container to your favorite registry.

  1. $  make docker-build docker-push IMG=<some-registry>/<project-name>:tag

NOTE: To allow the cluster pull the image the repository needs to be set as public or you must configure an image pull secret

Run the Operator

There are three ways to run the operator:

1. Run locally outside the cluster

Execute the following command, which install your CRDs and run the manager locally:

  1. make install run

2. Run as a Deployment inside the cluster

Build and push the image

Build and push the image:

  1. export USERNAME=<quay-namespace>
  2. make docker-build docker-push IMG=quay.io/$USERNAME/memcached-operator:v0.0.1

Note: The name and tag of the image (IMG=<some-registry>/<project-name>:tag) in both the commands can also be set in the Makefile. Modify the line which has IMG ?= controller:latest to set your desired default image name.

Deploy the operator

By default, a new namespace is created with name <project-name>-system, i.e. memcached-operator-system and will be used for the deployment.

Run the following to deploy the operator. This will also install the RBAC manifests from config/rbac.

  1. make deploy IMG=quay.io/$USERNAME/memcached-operator:v0.0.1

Verify that the memcached-operator is up and running:

  1. $ kubectl get deployment -n memcached-operator-system
  2. NAME                                    READY   UP-TO-DATE   AVAILABLE   AGE
  3. memcached-operator-controller-manager   1/1     1            1           8m

3. Deploy your Operator with OLM

First, install OLM:

  1. operator-sdk olm install

Then bundle your operator and push the bundle image:

  1. make bundle IMG=$OPERATOR_IMG
  2. # Note the "-bundle" component in the image name below.
  3. export BUNDLE_IMG="quay.io/$USERNAME/memcached-operator-bundle:v0.0.1"
  4. make bundle-build BUNDLE_IMG=$BUNDLE_IMG
  5. make docker-push IMG=$BUNDLE_IMG

Finally, run your bundle:

  1. operator-sdk run bundle $BUNDLE_IMG

Check out the docs for a deep dive into operator-sdk‘s OLM integration.

Create a Memcached CR

Update the sample Memcached CR manifest at config/samples/cache_v1alpha1_memcached.yaml and define the spec as the following:

  1. apiVersion: cache.example.com/v1alpha1
  2. kind: Memcached
  3. metadata:
  4.   name: memcached-sample
  5. spec:
  6.   size: 3

Create the CR:

  1. kubectl apply -f config/samples/cache_v1alpha1_memcached.yaml

Ensure that the memcached operator creates the deployment for the sample CR with the correct size:

  1. $ kubectl get deployment
  2. NAME                                    READY   UP-TO-DATE   AVAILABLE   AGE
  3. memcached-sample                        3/3     3            3           1m

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

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

Update the size

Update config/samples/cache_v1alpha1_memcached.yaml to change the spec.size field in the Memcached CR from 3 to 5:

  1. kubectl patch memcached memcached-sample -p '{"spec":{"size": 5}}' --type=merge

Confirm that the operator changes the deployment size:

  1. $ kubectl get deployment
  2. NAME                                    READY   UP-TO-DATE   AVAILABLE   AGE
  3. memcached-sample                        5/5     5            5           3m

Cleanup

Call the following to delete all deployed resources:

  1. make undeploy

Next Steps

We recommend reading through the our Ansible development section for tips and tricks, including how to run the operator locally.

In this tutorial, the scaffolded watches.yaml could be used as-is, but has additional optional features. See watches reference.

For brevity, some of the scaffolded files were left out of this guide. See Scaffolding Reference

This example built a namespaced scope operator, but Ansible operators can also be used with cluster-wide scope.

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 guide.

Last modified January 28, 2021: doc: improve/fix memcached go tutorial (#4021) (7845eec3)