4.2. Creating Ansible-based Operators

Procedure

1. Create a new Operator project. A namespace-scoped Operator watches and manages resources in a single namespace. Namespace-scoped Operators are preferred because of their flexibility. They enable decoupled upgrades, namespace isolation for failures and monitoring, and differing API definitions.

   To create a new Ansible-based, namespace-scoped memcached-operator project and change to the new directory, use the following commands:

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

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   $ cd memcached-operator

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   This creates the memcached-operator project specifically for watching the Memcached resource with API version example.com/v1apha1 and kind Memcached.

2. Customize the Operator logic.

   For this example, the memcached-operator executes the following reconciliation logic for each Memcached custom resource (CR):

   • Create a memcached deployment if it does not exist.
   • Ensure that the deployment size is the same as specified by the Memcached CR.

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

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

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   You can optionally customize the following logic in the watches.yaml file:

   1. Specifying a role option configures the Operator to use this specified path when launching ansible-runner with an Ansible role. By default, the operator-sdk new command fills in an absolute path to where your role should go:

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

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   2. Specifying a playbook option in the watches.yaml file configures 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

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3. Build the Memcached Ansible role.

   Modify the generated Ansible role under the roles/memcached/ directory. This Ansible role controls the logic that is executed when a resource is modified.

   1. Define the Memcached spec.

      Defining the spec for an Ansible-based Operator can be done entirely in Ansible. The Ansible Operator passes all key-value pairs listed in the CR spec field along to Ansible as variables. The names of all variables in the spec field are converted to snake case (lowercase with an underscore) by the Operator before running Ansible. For example, serviceAccount in the spec becomes service_account in Ansible.

      提示

      You should perform some type validation in Ansible on the variables to ensure that your application is receiving expected input.

      In case the user does not set the spec field, set a default by modifying the roles/memcached/defaults/main.yml file:

      size: 1

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   2. Define the Memcached deployment.

      With the Memcached spec now defined, you can define what Ansible is actually executed on resource changes. Because this is an Ansible role, the default behavior executes the tasks in the roles/memcached/tasks/main.yml file.

      The goal is for Ansible to create a deployment if it does not exist, which runs the memcached:1.4.36-alpine image. Ansible 2.7+ supports the k8s Ansible module, which this example leverages to control the deployment definition.

      Modify the roles/memcached/tasks/main.yml to match 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

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      注意

      This example used the size variable to control the number of replicas of the Memcached deployment. This example sets the default to 1, but any user can create a CR that overwrites the default.

4. Deploy the CRD.

   Before running the Operator, Kubernetes needs to know about the new custom resource definition (CRD) that the Operator will be watching. Deploy the Memcached CRD:

   $ oc create -f deploy/crds/cache.example.com_memcacheds_crd.yaml

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5. Build and run the Operator.

   There are two ways to build and run the Operator:

   • As a pod inside a Kubernetes cluster.
   • As a Go program outside the cluster using the operator-sdk up command.

   Choose one of the following methods:

   1. Run as a pod inside a Kubernetes cluster. This is the preferred method for production use.

      1. Build the memcached-operator image and push it to a registry:

         $ operator-sdk build quay.io/example/memcached-operator:v0.0.1

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         $ podman push quay.io/example/memcached-operator:v0.0.1

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      2. Deployment manifests are generated in the deploy/operator.yaml file. 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

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      3. Deploy the memcached-operator manifests:

         $ oc create -f deploy/service_account.yaml

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         $ oc create -f deploy/role.yaml

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         $ oc create -f deploy/role_binding.yaml

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         $ oc create -f deploy/operator.yaml

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      4. Verify that the memcached-operator deployment is up and running:

         $ oc get deployment

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         NAME                     DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
         memcached-operator       1         1         1            1           1m

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   2. Run outside the cluster. This method is preferred during the development cycle to speed up deployment and testing.

      Ensure that Ansible Runner and Ansible Runner HTTP Plug-in are installed or else you will see unexpected errors from Ansible Runner when a CR is created.

      It is also important that the role path referenced in the watches.yaml file exists on your machine. Because normally a container is used where the role is put on disk, the role must be manually copied to the configured Ansible roles path (for example /etc/ansible/roles).

      1. To run the Operator locally with the default Kubernetes configuration file present at $HOME/.kube/config:

         $ operator-sdk run --local

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         To run the Operator locally with a provided Kubernetes configuration file:

         $ operator-sdk run --local --kubeconfig=config

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6. Create a Memcached CR.

   1. Modify the deploy/crds/cache_v1alpha1_memcached_cr.yaml file as shown and create a Memcached CR:

      $ cat deploy/crds/cache_v1alpha1_memcached_cr.yaml

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      Example output

      apiVersion: "cache.example.com/v1alpha1"
      kind: "Memcached"
      metadata:
        name: "example-memcached"
      spec:
        size: 3

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      $ oc apply -f deploy/crds/cache_v1alpha1_memcached_cr.yaml

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   2. Ensure that the memcached-operator creates the deployment for the CR:

      $ oc get deployment

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      Example output

      NAME                     DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
      memcached-operator       1         1         1            1           2m
      example-memcached        3         3         3            3           1m

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   3. Check the pods to confirm three replicas were created:

      $ oc get pods

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      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

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7. Update the size.

   1. Change the spec.size field in the memcached CR from 3 to 4 and apply the change:

      $ cat deploy/crds/cache_v1alpha1_memcached_cr.yaml

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      Example output

      apiVersion: "cache.example.com/v1alpha1"
      kind: "Memcached"
      metadata:
        name: "example-memcached"
      spec:
        size: 4

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      $ oc apply -f deploy/crds/cache_v1alpha1_memcached_cr.yaml

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   2. Confirm that the Operator changes the deployment size:

      $ oc get deployment

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      Example output

      NAME                 DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
      example-memcached    4         4         4            4           5m

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8. Clean up the resources:

   $ oc delete -f deploy/crds/cache_v1alpha1_memcached_cr.yaml

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   $ oc delete -f deploy/operator.yaml

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   $ oc delete -f deploy/role_binding.yaml

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   $ oc delete -f deploy/role.yaml

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   $ oc delete -f deploy/service_account.yaml

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   $ oc delete -f deploy/crds/cache_v1alpha1_memcached_crd.yaml

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Procedure

1. To track CR status manually from your application, update the watches.yaml file with a manageStatus field set to false:

   - version: v1
     group: api.example.com
     kind: Test1
     role: Test1
     manageStatus: false

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2. Use the operator_sdk.util.k8s_status Ansible module to update the subresource. For example, to update with key test1 and value test2, operator_sdk.util can be used as shown:

   - operator_sdk.util.k8s_status:
       api_version: app.example.com/v1
       kind: Test1
       name: "{{ meta.name }}"
       namespace: "{{ meta.namespace }}"
       status:
         test1: test2

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   Collections can also be declared in the meta/main.yml for the role, which is included for new scaffolded Ansible Operators:

   collections:
     - operator_sdk.util

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   Declaring collections in the role meta allows you to invoke the k8s_status module directly:

   k8s_status:
     <snip>
     status:
       test1: test2

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