Ansible Operator Tutorial
NOTE: If your project was created with an operator-sdk version prior to v1.0.0
please migrate, or consult the legacy docs.
Prerequisites
- Go through the installation guide.
- Make sure your user is authorized with
cluster-adminpermissions. - An accessible image registry for various operator images (ex. hub.docker.com,
quay.io) and be logged in to your command line environment.
example.comis used as the registry Docker Hub namespace in these examples. Replace it with another value if using a different registry or namespace.- Authentication and certificates if the registry is private or uses a custom CA.
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 CR’s pods
Create a new project
Use the CLI to create a new memcached-operator project:
mkdir memcached-operator
cd memcached-operator
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.
Next, we will create a Memcached API.
operator-sdk create api --group cache --version v1alpha1 --kind Memcached --generate-role
The scaffolded operator has the following structure:
MemcachedCustom Resource Definition, and a sampleMemcachedresource.- A “Manager” that reconciles the state of the cluster to the desired state
- A reconciler, which is an Ansible Role or Playbook.
- A
watches.yamlfile, which connects theMemcachedresource to thememcachedAnsible 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:
---
- name: start memcached
kubernetes.core.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 will:
- Ensure a memcached Deployment exists
- Set the Deployment size
Note that the tasks in this Ansible role file are what actually defines the behavior of the spec and status of the memcached custom resource.
As Kubernetes allows entry of arbitrary fields when creating resources, we don’t need to actually create specific fields in the CRD.
While we won’t be doing this in this tutorial, it is recommended to also define these fields in the CRD, so that Kubernetes users
can see the fields that will be used when using the custom resource.
It is also good practice to set default values for variables used in Ansible
Roles, so edit roles/memcached/defaults/main.yml:
---
# defaults file for Memcached
size: 1
Finally, update the Memcached sample, config/samples/cache_v1alpha1_memcached.yaml:
apiVersion: cache.example.com/v1alpha1
kind: Memcached
metadata:
name: memcached-sample
spec:
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 the expected input.
Configure the operator’s image registry
All that remains is to build and push the operator image to the desired image registry.
Your Makefile composes image tags either from values written at project initialization or from the CLI.
In particular, IMAGE_TAG_BASE lets you define a common image registry, namespace, and partial name
for all your image tags. Update this to another registry and/or namespace if the current value is incorrect.
Afterwards you can update the IMG variable definition like so:
-IMG ?= controller:latest
+IMG ?= $(IMAGE_TAG_BASE):$(VERSION)
Once done, you do not have to set IMG or any other image variable in the CLI. The following command will
build and push an operator image tagged as example.com/memcached-operator:v0.0.1 to Docker Hub:
make docker-build docker-push
Run the Operator
There are three ways to run the operator:
- As a Go program outside a cluster
- As a Deployment inside a Kubernetes cluster
- Managed by the Operator Lifecycle Manager (OLM) in bundle format
1. Run locally outside the cluster
Execute the following command, which installs your CRDs and runs the manager locally:
make install run
2. Run as a Deployment inside the cluster
By default, a new namespace is created with name <project-name>-system, ex. memcached-operator-system, and will be used for the deployment.
Commonly, Operator authors may need to modify config/rbac in order to
give their Operator the necessary permissions to reconcile.
Run the following to customize the manifests and deploy the operator.
make deploy
The scaffolded Makefile uses kustomize to apply custom
configurations and generate manifests from the config/ directory, which are
piped to kubectl. Run the following command to see the manifests that were
applied to the cluster.
kustomize build config/default
Verify that the memcached-operator is up and running:
$ kubectl get deployment -n memcached-operator-system
NAME READY UP-TO-DATE AVAILABLE AGE
memcached-operator-controller-manager 1/1 1 1 8m
3. Deploy your Operator with OLM
First, install OLM:
operator-sdk olm install
Bundle your operator, then build and push the bundle image. The bundle target generates a bundle
in the bundle directory containing manifests and metadata defining your operator.
bundle-build and bundle-push build and push a bundle image defined by bundle.Dockerfile.
make bundle bundle-build bundle-push
Finally, run your bundle. If your bundle image is hosted in a registry that is private and/or has a custom CA, these configuration steps must be complete.
operator-sdk run bundle example.com/memcached-operator-bundle:v0.0.1
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:
apiVersion: cache.example.com/v1alpha1
kind: Memcached
metadata:
name: memcached-sample
spec:
size: 3
Create the CR:
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:
$ kubectl get deployment
NAME READY UP-TO-DATE AVAILABLE AGE
memcached-sample 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
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
$ kubectl get memcached/memcached-sample -o yaml
apiVersion: cache.example.com/v1alpha1
kind: Memcached
metadata:
creationTimestamp: "2021-03-17T19:54:42Z"
generation: 1
managedFields:
- apiVersion: cache.example.com/v1alpha1
fieldsType: FieldsV1
fieldsV1:
f:status:
.: {}
f:conditions: {}
manager: ansible-operator
operation: Update
time: "2021-03-17T19:54:42Z"
- apiVersion: cache.example.com/v1alpha1
fieldsType: FieldsV1
fieldsV1:
f:spec:
.: {}
f:size: {}
manager: kubectl
operation: Update
time: "2021-03-17T19:54:42Z"
name: memcached-sample
namespace: default
resourceVersion: "1008"
uid: 4b023125-132a-44e3-80de-20801c7a9268
spec:
size: 3
status:
conditions:
- ansibleResult:
changed: 0
completion: 2021-03-17T19:54:54.890394
failures: 0
ok: 1
skipped: 0
lastTransitionTime: "2021-03-17T19:54:42Z"
message: Awaiting next reconciliation
reason: Successful
status: "True"
type: Running
Update the size
Update config/samples/cache_v1alpha1_memcached.yaml to change the spec.size field in the Memcached CR from 3 to 5:
kubectl patch memcached memcached-sample -p '{"spec":{"size": 5}}' --type=merge
Confirm that the operator changes the deployment size:
$ kubectl get deployment
NAME READY UP-TO-DATE AVAILABLE AGE
memcached-sample 5/5 5 5 3m
Cleanup
Run the following to delete all deployed resources:
kubectl delete -f config/samples/cache_v1alpha1_memcached.yaml
make undeploy
Next Steps
We recommend reading through the 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 the 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.