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User Guide

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

Prerequisites

  • git
  • docker version 17.03+.
  • kubectl version v1.9.0+.
  • ansible version v2.6.0+
  • ansible-runner version v1.1.0+
  • ansible-runner-http version v1.0.0+
  • dep version v0.5.0+. (Optional if you aren't installing from source)
  • go version v1.10+. (Optional if you aren't installing from source)
  • 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 Ansible-based memcached-operator project:

$ operator-sdk new memcached-operator --api-version=cache.example.com/v1alpha1 --kind=Memcached --type=ansible
$ 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.

Operator scope

A namespace-scoped operator (the default) watches and manages resources in a single namespace, whereas a cluster-scoped operator watches and manages resources cluster-wide. Namespace-scoped operators are preferred because of their flexibility. They enable decoupled upgrades, namespace isolation for failures and monitoring, and differing API definitions. However, there are use cases where a cluster-scoped operator may make sense. For example, the cert-manager operator is often deployed with cluster-scoped permissions and watches so that it can manage issuing certificates for an entire cluster.

If you'd like to create your memcached-operator project to be cluster-scoped use the following operator-sdk new command instead:

$ operator-sdk new memcached-operator --cluster-scoped --api-version=cache.example.com/v1alpha1 --kind=Memcached --type=ansible

Customize the operator logic

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

  • Create a memcached Deployment if it doesn't exist
  • Ensure that the Deployment size is the same as specified by the Memcached CR

Watch the Memcached CR

By default, the memcached-operator watches Memcached resource events as shown in watches.yaml and executes Ansible Role Memached:

---
- version: v1alpha1
  group: cache.example.com
  kind: Memcached

Options

Role Specifying a role option in watches.yaml will configure the operator to use this specified path when launching ansible-runner with an Ansible Role. By default, the new command will fill in an absolute path to where your role should go.

---
- version: v1alpha1
  group: cache.example.com
  kind: Memcached
  role: /opt/ansible/roles/Memcached

Playbook Specifying a playbook option in watches.yaml will configure the operator to use this specified path when launching ansible-runner with an Ansible Playbook

---
- version: v1alpha1
  group: cache.example.com
  kind: Memcached
  playbook: /opt/ansible/playbook.yaml

Building the Memcached Ansible Role

The first thing to do is to modify the generated Ansible role under roles/Memcached. This Ansible Role controls the logic that is executed when a resource is modified.

Define the Memcached spec

Defining the spec for an Ansible Operator can be done entirely in Ansible. The Ansible Operator will simply pass all key value pairs listed in the Custom Resource spec field along to Ansible as variables. 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. It is recommended that you perform some type validation in Ansible on the variables to ensure that your application is receiving expected input.

First, set a default in case the user doesn't set the spec field by modifying roles/Memcached/defaults/main.yml:

size: 1

Defining the Memcached deployment

Now that we have the spec defined, we can define what Ansible is actually executed on resource changes. Since this is an Ansible Role, the default behavior will be to execute the tasks in roles/Memcached/tasks/main.yml. We want Ansible to create a deployment if it does not exist which runs the memcached:1.4.36-alpine image. Ansible 2.5+ supports the k8s Ansible Module which we will leverage to control the deployment definition.

Modify roles/Memcached/tasks/main.yml to look like the following:

---
- name: start memcached
  k8s:
    definition:
      kind: Deployment
      apiVersion: apps/v1
      metadata:
        name: '{{ meta.name }}-memcached'
        namespace: '{{ 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

It is important to note that we used the size variable to control how many replicas of the Memcached deployment we want. We set the default to 1, but any user can create a Custom Resource that overwrites the default.

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/crds/cache_v1alpha1_memcached_crd.yaml

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

  • As a pod inside a Kubernetes cluster
  • As a go program outside the cluster using operator-sdk

1. Run as a pod inside a Kubernetes cluster

Running as a 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
$ docker push quay.io/example/memcached-operator:v0.0.1

Kubernetes deployment manifests are generated in deploy/operator.yaml. The deployment image in this file needs to be modified from the placeholder REPLACE_IMAGE to the previous built image. To do this run:

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

If you created your operator using --cluster-scoped=true, update the service account namespace in the generated ClusterRoleBinding to match where you are deploying your operator.

$ export OPERATOR_NAMESPACE=$(kubectl config view --minify -o jsonpath='{.contexts[0].context.namespace}')
$ sed -i "s|REPLACE_NAMESPACE|$OPERATOR_NAMESPACE|g" deploy/role_binding.yaml

Note
If you are performing these steps on OSX, use the following commands instead:

$ sed -i "" 's|REPLACE_IMAGE|quay.io/example/memcached-operator:v0.0.1|g' deploy/operator.yaml
$ sed -i "" "s|REPLACE_NAMESPACE|$OPERATOR_NAMESPACE|g" deploy/role_binding.yaml

Deploy the memcached-operator:

$ kubectl create -f deploy/service_account.yaml
$ kubectl create -f deploy/role.yaml
$ kubectl create -f deploy/role_binding.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 the development cycle to speed up deployment and testing.

Note: Ensure that Ansible Runner and Ansible Runner HTTP Plugin is installed or else you will see unexpected errors from Ansible Runner when a Custom Resource is created.

It is also important that the role path referenced in watches.yaml exists on your machine. Since we are normally used to using a container where the Role is put on disk for us, we need to manually copy our role to the configured Ansible Roles path (e.g /etc/ansible/roles.

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/crds/cache_v1alpha1_memcached_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 to confirm 3 replicas were created:

$ 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

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/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

Cleanup

Clean up the resources:

$ kubectl delete -f deploy/crds/cache_v1alpha1_memcached_cr.yaml
$ kubectl delete -f deploy/operator.yaml
$ kubectl delete -f deploy/role_binding.yaml
$ kubectl delete -f deploy/role.yaml
$ kubectl delete -f deploy/service_account.yaml
$ kubectl delete -f deploy/crds/cache_v1alpha1_memcached_cr.yaml