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Ansible Developer Guide for Operator SDK

This document provides some useful information and tips for a developer creating an operator powered by Ansible.

Getting started with the k8s Ansible modules

Since we are interested in using Ansible for the lifecycle management of our application on Kubernetes, it is beneficial for a developer to get a good grasp of the k8s Ansible module. This Ansible module allows a developer to either leverage their existing Kubernetes resource files (written in YaML) or express the lifecycle management in native Ansible. One of the biggest benefits of using Ansible in conjunction with existing Kubernetes resource files is the ability to use Jinja templating so that you can customize deployments with the simplicity of a few variables in Ansible.

The easiest way to get started is to install the modules on your local machine and test them using a playbook.

Installing the k8s Ansible modules

To install the k8s Ansible modules, one must first install Ansible 2.6+. On Fedora/Centos:

$ sudo dnf install ansible

In addition to Ansible, a user must install the OpenShift Restclient Python package. This can be installed from pip:

$ pip3 install openshift

Testing the k8s Ansible modules locally

Sometimes it is beneficial for a developer to run the Ansible code from their local machine as opposed to running/rebuilding the operator each time. To do this, initialize a new project:

$ operator-sdk new --type ansible --kind Foo --api-version foo.example.com/v1alpha1 foo-operator
Create foo-operator/tmp/init/galaxy-init.sh
Create foo-operator/tmp/build/Dockerfile
Create foo-operator/tmp/build/test-framework/Dockerfile
Create foo-operator/tmp/build/go-test.sh
Rendering Ansible Galaxy role [foo-operator/roles/Foo]...
Cleaning up foo-operator/tmp/init
Create foo-operator/watches.yaml
Create foo-operator/deploy/rbac.yaml
Create foo-operator/deploy/crd.yaml
Create foo-operator/deploy/cr.yaml
Create foo-operator/deploy/operator.yaml
Run git init ...
Initialized empty Git repository in /home/dymurray/go/src/github.com/dymurray/opsdk/foo-operator/.git/
Run git init done

$ cd foo-operator

Modify roles/Foo/tasks/main.yml with desired Ansible logic. For this example we will create and delete a namespace with the switch of a variable:

---
- name: set example-memcached namespace to {{ state }}
  k8s:
    api_version: v1
    kind: Namespace
    name: example-memcached
    state: "{{ state }}"
  ignore_errors: true

note: Setting ignore_errors: true is done so that deleting a nonexistent project doesn't error out.

Modify roles/Foo/defaults/main.yml to set state to present by default.

---
state: present

Create an Ansible playbook playbook.yml in the top-level directory which includes role Foo:

---
- hosts: localhost
  roles:
    - Foo

Run the playbook:

$ ansible-playbook playbook.yml
 [WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'


PLAY [localhost] ***************************************************************************

TASK [Gathering Facts] *********************************************************************
ok: [localhost]

Task [Foo : set example-memcached namespace to present]
changed: [localhost]

PLAY RECAP *********************************************************************************
localhost                  : ok=2    changed=1    unreachable=0    failed=0

Check that the namespace was created:

$ kubectl get namespace
NAME          	           STATUS    AGE
default       	           Active    28d
kube-public   		   Active    28d
kube-system   	           Active    28d
example-memcached          Active    3s

Rerun the playbook setting state to absent:

$ ansible-playbook playbook.yml --extra-vars state=absent
 [WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'


PLAY [localhost] ***************************************************************************

TASK [Gathering Facts] *********************************************************************
ok: [localhost]

Task [Foo : set example-memcached namespace to absent]
changed: [localhost]

PLAY RECAP *********************************************************************************
localhost                  : ok=2    changed=1    unreachable=0    failed=0

Check that the namespace was deleted:

$ kubectl get namespace
NAME          STATUS    AGE
default       Active    28d
kube-public   Active    28d
kube-system   Active    28d

Using Ansible inside of an Operator

Now that we have demonstrated using the Ansible Kubernetes modules, we want to trigger this Ansible logic when a custom resource changes. In the above example, we want to map a role to a specific Kubernetes resource that the operator will watch. This mapping is done in a file called watches.yaml.

Custom Resource file

The Custom Resource file format is Kubernetes resource file. The object has mandatory fields:

apiVersion: The version of the Custom Resource that will be created.

kind: The kind of the Custom Resource that will be created

metadata: Kubernetes specific metadata to be created

spec: This is the key-value list of variables which are passed to Ansible. This field is optional and will be empty by default.

annotations: Kubernetes specific annotations to be appended to the CR. See the below section for Ansible Operator specific annotations.

Ansible Operator annotations

This is the list of CR annotations which will modify the behavior of the operator:

ansible.operator-sdk/reconcile-period: Used to specify the reconciliation interval for the CR. This value is parsed using the standard Golang package time. Specifically ParseDuration is used which will apply the default suffix of s giving the value in seconds.

Example:

apiVersion: "foo.example.com/v1alpha1"
kind: "Foo"
metadata:
  name: "example"
annotations:
  ansible.operator-sdk/reconcile-period: "30s"

Testing an Ansible operator locally

Once a developer is comfortable working with the above workflow, it will be beneficial to test the logic inside of an operator. To accomplish this, we can use operator-sdk up local from the top-level directory of our project. The up local command reads from ./watches.yaml and uses ~/.kube/config to communicate with a Kubernetes cluster just as the k8s modules do. This section assumes the developer has read the Ansible Operator user guide and has the proper dependencies installed.

Since up local reads from ./watches.yaml, there are a couple options available to the developer. If role is left alone (by default /opt/ansible/roles/<name>) the developer must copy the role over to /opt/ansible/roles from the operator directly. This is cumbersome because changes will not be reflected from the current directory. It is recommended that the developer instead change the role field to point to the current directory and simply comment out the existing line:

- version: v1alpha1
  group: foo.example.com
  kind: Foo
  #  role: /opt/ansible/roles/Foo
  role: /home/user/foo-operator/Foo

Create a Custom Resource Definition (CRD) and proper Role-Based Access Control (RBAC) definitions for resource Foo. operator-sdk auto-generates these files inside of the deploy folder:

$ kubectl create -f deploy/crds/foo.example.com_foos_crd.yaml
$ kubectl create -f deploy/service_account.yaml
$ kubectl create -f deploy/role.yaml
$ kubectl create -f deploy/role_binding.yaml

Run the up local command:

$ operator-sdk up local
INFO[0000] Go Version: go1.10.3
INFO[0000] Go OS/Arch: linux/amd64
INFO[0000] operator-sdk Version: 0.0.6+git
INFO[0000] Starting to serve on 127.0.0.1:8888

INFO[0000] Watching foo.example.com/v1alpha1, Foo, default

Now that the operator is watching resource Foo for events, the creation of a Custom Resource will trigger our Ansible Role to be executed. Take a look at deploy/cr.yaml:

apiVersion: "foo.example.com/v1alpha1"
kind: "Foo"
metadata:
  name: "example"

Since spec is not set, Ansible is invoked with no extra variables. The next section covers how extra variables are passed from a Custom Resource to Ansible. This is why it is important to set sane defaults for the operator.

Create a Custom Resource instance of Foo with default var state set to present:

$ kubectl create -f deploy/cr.yaml

Check that namespace example-memcached was created:

$ kubectl get namespace
NAME          	           STATUS    AGE
default       		   Active    28d
kube-public   		   Active    28d
kube-system   		   Active    28d
example-memcached          Active    3s

Modify deploy/cr.yaml to set state to absent:

apiVersion: "foo.example.com/v1alpha1"
kind: "Foo"
metadata:
  name: "example"
spec:
  state: "absent"

Apply the changes to Kubernetes and confirm that the namespace is deleted:

$ kubectl apply -f deploy/cr.yaml
$ kubectl get namespace
NAME          STATUS    AGE
default       Active    28d
kube-public   Active    28d
kube-system   Active    28d

Testing an Ansible operator on a cluster

Now that a developer is confident in the operator logic, testing the operator inside of a pod on a Kubernetes cluster is desired. Running as a pod inside a Kubernetes cluster is preferred for production use.

To build the foo-operator image and push it to a registry:

$ operator-sdk build quay.io/example/foo-operator:v0.0.1
$ docker push quay.io/example/foo-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/foo-operator:v0.0.1|g' deploy/operator.yaml

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

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

Deploy the foo-operator:

$ kubectl create -f deploy/crds/foo.example.com_foos_crd.yaml # if CRD doesn't exist already
$ 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 foo-operator is up and running:

$ kubectl get deployment
NAME                     DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
foo-operator       1         1         1            1           1m

Viewing the Ansible logs

The foo-operator deployment creates a Pod with two containers, operator and ansible. The ansible container exists only to expose the standard Ansible stdout logs that most Ansible users will be familiar with. In order to see the logs from a particular container, you can run

kubectl logs deployment/foo-operator -c ansible
kubectl logs deployment/foo-operator -c operator

The ansible logs contain all of the information about the Ansible run and will make it much easier to debug issues within your Ansible tasks, whereas the operator logs will contain much more detailed information about the Ansible Operator's internals and interface with Kubernetes.

Custom Resource Status Management

The operator will automatically update the CR's status subresource with generic information about the previous Ansible run. This includes the number of successful and failed tasks and relevant error messages as seen below:

status:
  conditions:
    - ansibleResult:
      changed: 3
      completion: 2018-12-03T13:45:57.13329
      failures: 1
      ok: 6
      skipped: 0
    lastTransitionTime: 2018-12-03T13:45:57Z
    message: 'Status code was -1 and not [200]: Request failed: <urlopen error [Errno
      113] No route to host>'
    reason: Failed
    status: "True"
    type: Failure
  - lastTransitionTime: 2018-12-03T13:46:13Z
    message: Running reconciliation
    reason: Running
    status: "True"
    type: Running

Ansible Operator also allows you as the developer to supply custom status values with the k8s_status Ansible Module, which is included in operator_sdk util collection.

This allows the developer to update the status from within Ansible with any key/value pair as desired. By default, Ansible Operator will always include the generic Ansible run output as shown above. If you would prefer your application not update the status with Ansible output and would prefer to track the status manually from your application, then simply update the watches file with manageStatus:

- version: v1
  group: api.example.com
  kind: Foo
  role: /opt/ansible/roles/Foo
  manageStatus: false

The simplest way to invoke the k8s_status module is to use its fully qualified collection name (fqcn). To update the status subresource with key foo and value bar, k8s_status can be used as shown:

- operator_sdk.util.k8s_status:
    api_version: app.example.com/v1
    kind: Foo
    name: "{{ meta.name }}"
    namespace: "{{ meta.namespace }}"
    status:
      foo: bar

Collections can also be declared in the role's meta/main.yml, which is included for new scaffolded ansible operators.

collections:
  - operator_sdk.util

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

- k8s_status:
    <snip>
    status:
      foo: bar

Ansible Operator Conditions

The Ansible Operator has a set of conditions which it will use as it performs its reconciliation procedure. There are only a few main conditions:

  • Running - the Ansible Operator is currently running the Ansible for reconciliation.

  • Successful - if the run has finished and there were no errors, the Ansible Operator will be marked as Successful. It will then wait for the next reconciliation action, either the reconcile period, dependent watches triggers or the resource is updated.

  • Failed - if there is any error during the reconciliation run, the Ansible Operator will be marked as Failed with the error message from the error that caused this condition. The error message is the raw output from the Ansible run for reconciliation. If the failure is intermittent, often times the situation can be resolved when the Operator reruns the reconciliation loop.

Please look over the following sections for help debugging an Ansible Operator:

Using k8s_status Ansible module with up local

This section covers the required steps to using the k8s_status Ansible module with operator-sdk up local. If you are unfamiliar with managing status from the Ansible Operator, see the proposal for user-driven status management.

If your operator takes advantage of the k8s_status Ansible module and you are interested in testing the operator with operator-sdk up local, then you will need to install the collection locally.

$ ansible-galaxy collection install operator_sdk.util

Extra vars sent to Ansible

The extra vars that are sent to Ansible are managed by the operator. The spec section will pass along the key-value pairs as extra vars. This is equivalent to how above extra vars are passed in to ansible-playbook. The operator also passes along additional variables under the meta field for the name of the CR and the namespace of the CR.

For the CR example:

apiVersion: "app.example.com/v1alpha1"
kind: "Database"
metadata:
  name: "example"
spec:
  message:"Hello world 2"
  newParameter: "newParam"

The structure passed to Ansible as extra vars is:

{ "meta": {
        "name": "<cr-name>",
        "namespace": "<cr-namespace>",
  },
  "message": "Hello world 2",
  "new_parameter": "newParam",
  "_app_example_com_database": {
     <Full CR>
   },
  "_app_example_com_database_spec": {
     <Full CR .spec>
   },
}

message and newParameter are set in the top level as extra variables, and meta provides the relevant metadata for the Custom Resource as defined in the operator. The meta fields can be accesses via dot notation in Ansible as so:

---
- debug:
    msg: "name: {{ meta.name }}, {{ meta.namespace }}"