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Showing content from https://sdk.operatorframework.io/docs/building-operators/ansible/testing-guide below:

Ansible Based Operator Testing with Molecule

To begin, you should have:

• The latest version of the operator-sdk installed.
• Docker installed and running
• Molecule >= v3.0
• Ansible >= v2.9
• The Python Kubernetes client
• An initialized Ansible Operator project, with the molecule directory present.

NOTE If you initialized a project with a previous version of operator-sdk, you can generate a new dummy project and copy in the molecule directory. Just be sure to generate the dummy project with the same api-version and kind, or some of the generated files will not work without modification. Your top-level project structure should look like this:

```
.
├── config
├── Dockerfile
├── Makefile
├── molecule
├── playbooks
├── PROJECT
├── requirements.yml
├── roles
└── watches.yaml

```

• The Ansible content specified in requirements.yml will also need to be installed. You can install them with ansible-galaxy collection install -r requirements.yml

If you look into the molecule directory, you will see four directories (default, test-local,cluster, templates). The default, test-local, and cluster directories contain a set of files that together make up what is known as a molecule scenario. The templates directory contains Jinja templates that are used by multiple scenarios to configure the Kubernetes cluster.

Our molecule scenarios have the following basic structure:

.
├── molecule.yml
├── prepare.yml
├── converge.yml
└── verify.yml

• molecule.yml is a configuration file for molecule. It defines what driver to use to stand up an environment and the associated configuration, linting rules, and a variety of other configuration options. For full documentation on the options available here, see the molecule configuration documentation

• prepare.yml is an Ansible playbook that is run once during the set up of a scenario. You can put any arbitrary Ansible in this playbook. It is used for one-time configuration of your test environment, for example, creating the cluster-wide CustomResourceDefinition that your Operator will watch.

• converge.yml is an Ansible playbook that contains your core logic for the scenario. In a normal molecule scenario, this would import and run the associated role. For Ansible Operators, we mostly use this to create the Kubernetes resources necessary to deploy your operator into Kubernetes.

Below we will walk through the structure and function of each file for each scenario.

The default scenario is intended for use during the development of your Ansible role or playbook, and will run it outside of the context of an operator. You can run this scenario with molecule test or molecule converge. There is no corresponding operator-sdk command for this scenario.

The scenario has the following structure:

molecule/default
├── molecule.yml
├── prepare.yml
├── converge.yml
└── verify.yml

• molecule.yml for this scenario tells molecule to use the docker driver to bring up a Kubernetes-in-Docker container, and by default exposes the API on the host’s port 9443. It also specifies a few inventory and environment variables which are used in prepare.yml and converge.yml.

• prepare.yml ensures that a kubeconfig properly configured to connect to the Kubernetes-in-Docker cluster exists and is mapped to the proper port, and also waits for the Kubernetes API to become available before allowing testing to begin.

• converge.yml imports and runs your role or playbook.

• verify.yml is an Ansible playbook where you can put tasks to verify that the state of your cluster matches what you expect.

There are a few parameters you can tweak at runtime to change the behavior of your molecule run. You can change these parameters by setting the environment variable before invoking molecule.

The options supported by the default scenario are:

The cluster scenario runs an end-to-end test of your operator against an existing cluster. The operator image needs to be available to the cluster for this scenario to succeed. This scenario will deploy your CRDs, RBAC, and operator into the cluster, and then creates an instance of your CustomResource and runs your assertions to make sure the Operator responded properly.

You can run this scenario with molecule test or molecule converge. There is no corresponding operator-sdk command for this scenario.

The scenario has the following structure:

molecule/default
├── molecule.yml
├── create.yml
├── prepare.yml
├── converge.yml
├── verify.yml
└── destroy.yml

• molecule.yml for this scenario uses the delegated driver, and does not spin up any additional infrastructure.

• create.yml is a no-op, but must be present for the delegated driver to work.

• prepare.yml ensures the CRD, namespace, and RBAC resources are present in the cluster.

• converge.yml creates your operator deployment, based on the template in molecule/templates/operator.yaml.j2.

• verify.yml is an Ansible playbook where you can put tasks to verify that the state of your cluster matches what you expect. By default, it creates a Custom Resource and waits for reconciliation to complete successfully. There is an example assertion present as well.

• destroy.yml ensures that the namespace, RBAC resources, and CRD are deleted at the end of the run.

There are a few parameters you can tweak at runtime to change the behavior of your molecule run. You can change these parameters by setting the environment variable before invoking molecule.

The options supported by the default scenario are:

The test-local scenario runs a full end-to-end test of your operator that does not require an existing cluster or external registry, and can run in CI environments that allow users to run privileged containers (such as Travis). It brings up a Kubernetes-in-docker cluster, builds your Operator, deploys it into the cluster, and then creates an instance of your CustomResource and runs your assertions to make sure the Operator responded properly. You can run this scenario with molecule test -s local, or with molecule converge -s test-local which will leave the environment up afterward.

The scenario has the following structure:

molecule/test-local
├── molecule.yml
├── prepare.yml
├── converge.yml
└── verify.yml

• molecule.yml for this scenario tells molecule to use the docker driver to bring up a Kubernetes-in-Docker container with the project root mounted, and exposes the API on the host’s port 10443. It also specifies a few inventory and environment variables which are used in prepare.yml and converge.yml. It is very similar to the default scenario’s configuration.

• prepare.yml first runs the prepare.yml from the default scenario to ensure the kubeconfig is present and the API is up. It then runs the prepare.yml from the cluster scenario to configure your cluster’s CRDs and RBAC.

• converge.yml connects to your Kubernetes-in-Docker container, and uses your mounted project root to build your Operator. This makes your Operator available to the cluster without needing to push it to an external registry. Then, it will ensure that a fresh deployment of your Operator is present in the cluster, using the template molecule/templates/operator.yaml.j2.

• verify.yml will run the verify.yml from the cluster scenario, as the main difference between the test-local and cluster scenarios is the method of deployment, but not the behavior of the operator.

There are a few parameters you can tweak at runtime to change the behavior of your molecule run. You can change these parameters by setting the environment variable before invoking molecule.

The options supported by the default scenario are:

The two most common molecule commands for testing during development are molecule test and molecule converge. molecule test performs a full loop, bringing a cluster up, preparing it, running your tasks, and tearing it down. molecule converge is more useful for iterative development, as it leaves your environment up between runs. This can cause unexpected problems if you end up corrupting your environment during testing, but running molecule destroy will reset it.

• molecule test performs a full loop, bringing a cluster up, preparing it, running your tasks, and tearing it down.
• molecule converge is more useful for iterative development, as it leaves your environment up between runs. This can cause unexpected problems if you end up corrupting your environment during testing, but running molecule destroy will reset it.

The default operator that is generated by operator-sdk new doesn’t do anything, so first we will need to add an Ansible task so that the Operator does something we can verify. For this example, we will create a simple ConfigMap with a single key. We’ll be adding the task to roles/example/tasks/main.yml, which should now look like this:

---
# tasks file for exampleapp
- name: create Example configmap
  kubernetes.core.k8s:
    definition:
      apiVersion: v1
      kind: ConfigMap
      metadata:
        name: 'test-data'
        namespace: '{{ ansible_operator_meta.namespace }}'
      data:
        hello: world

Now that our Operator actually does some work, we can add a corresponding assert to molecule/cluster/verify.yml. We’ll also add a debug message so that we can see what the ConfigMap looks like. The file should now look like this:

---

- name: Verify
  hosts: localhost
  connection: local
  tasks:
    - debug: var=cm
      vars:
        cm: '{{ lookup("kubernetes.core.k8s", api_version="v1", kind="ConfigMap", namespace=namespace, resource_name="test-data") }}'
    - assert:
        that: cm.data.hello == 'world'
      vars:
        cm: '{{ lookup("kubernetes.core.k8s", api_version="v1", kind="ConfigMap", namespace=namespace, resource_name="test-data") }}'

Now that we have a functional Operator, and an assertion of its behavior, we can verify that everything is working by running molecule test -s local.

These modules are handy for adding assertions and failure conditions to your Ansible Operator tests:

• assert
• fail

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