Developer’s Guide

Writing Validations

All validations are written in standard Ansible with a couple of extra meta-data to provide information to the validation framework.

For people not familiar with Ansible, get started with their excellent documentation.

After the generic explanation on writing validations is a couple of concrete examples.

Directory Structure

All validations consist of an Ansible role located in the roles directory and a playbook located in the playbooks directory.

  • the playbooks one contains all the validations playbooks you can run;

  • the lookup_plugins one is for custom Ansible look up plugins available to the validations;

  • the library one is for custom Ansible modules available to the validations;

  • the roles one contains all the necessary Ansible roles to validate your TripleO deployment;

Here is what the tree looks like:

  ├── first_validation.yaml
  ├── second_validation.yaml
  ├── third_validation.yaml
  └── etc...
  └── etc...
  └── etc...
  ├── first_role
  ├── second_role
  └── etc...

Sample Validation

Each validation is an Ansible playbook located in the playbooks directory calling his own Ansible role located in the roles directory. Each playbook have some metadata. Here is what a minimal validation would look like:

- hosts: undercloud
      name: Hello World
      description: This validation prints Hello World!
  - hello-world

It should be saved as playbooks/hello_world.yaml.

As shown here, the validation playbook requires three top-level directives: hosts, vars -> metadata and roles.

hosts specify which nodes to run the validation on. Based on the hosts.sample structure, the options can be all (run on all nodes), undercloud, allovercloud (all overcloud nodes), controller and compute.

The vars section serves for storing variables that are going to be available to the Ansible playbook. The validations API uses the metadata section to read each validation’s name and description. These values are then reported by the API.

The validations can be grouped together by specifying a groups metadata. Groups function similar to tags and a validation can thus be part of many groups. Here is, for example, how to have a validation be part of the pre-deployment and hardware groups:

    - pre-deployment
    - hardware

roles include the Ansible role, which contains all the tasks to run, associated to this validation. Each task is a YAML dictionary that must at minimum contain a name and a module to use. Module can be any module that ships with Ansible or any of the custom ones in the library directory.

The Ansible documentation on playbooks provides more detailed information.

Ansible Inventory

Dynamic inventory

Tripleo-validations ships with a dynamic inventory, which contacts the various OpenStack services to provide the addresses of the deployed nodes as well as the undercloud.

Just pass -i /usr/bin/tripleo-ansible-inventory to ansible-playbook command.

As the playbooks are located in their own directory and not at the same level as the roles, callback_plugins, library and lookup_plugins directories, you will have to export some Ansible variables first:

$ cd tripleo-validations/
$ export ANSIBLE_CALLBACK_PLUGINS="${PWD}/callback_plugins"
$ export ANSIBLE_ROLES_PATH="${PWD}/roles"
$ export ANSIBLE_LOOKUP_PLUGINS="${PWD}/lookup_plugins"
$ export ANSIBLE_LIBRARY="${PWD}/library"

$ ansible-playbook -i /usr/bin/tripleo-ansible-inventory playbooks/hello_world.yaml

Hosts file

When more flexibility than what the current dynamic inventory provides is needed or when running validations against a host that hasn’t been deployed via heat (such as the prep validations), it is possible to write a custom hosts inventory file. It should look something like this:






It will have a [group] section for each role (undercloud, controller, compute) listing all the nodes belonging to that group. It is also possible to create a group from other groups as done with [allovercloud:children] in the above example. If a validation specifies hosts: overcloud, it will be run on any node that belongs to the compute or controller groups. If a node happens to belong to both, the validation will only be run once.

Lastly, there is an [all:vars] section where to configure certain Ansible-specific options.

ansible_ssh_user will specify the user Ansible should SSH as. If that user does not have root privileges, it is possible to instruct it to use sudo by setting ansible_sudo to true.

Learn more at the Ansible documentation page for the Inventory

Custom Modules

In case the available Ansible modules don’t cover your needs, it is possible to write your own. Modules belong to the library directory.

Here is a sample module that will always fail

#!/usr/bin/env python

from ansible.module_utils.basic import AnsibleModule

if __name__ == '__main__':
    module = AnsibleModule(argument_spec={})
    module.fail_json(msg="This module always fails.")

Save it as library/ and use it in a validation like so:

...  # some tasks
- name: Running my custom module
...  # some other tasks

The name of the module in the validation my_module must match the file name (without extension):

The custom modules can accept parameters and do more complex reporting. Please refer to the guide on writing modules in the Ansible documentation.


Each custom module must be accompanied by the most complete unit tests possible.

Learn more at the Ansible documentation page about writing custom modules.

Running a validation

Running the validations require ansible and a set of nodes to run them against. These nodes need to be reachable from the operator’s machine and need to have an account it can ssh to and perform passwordless sudo.

The nodes need to be present in the static inventory file or available from the dynamic inventory script depending on which one the operator chooses to use. Check which nodes are available with:

$ source stackrc
$ tripleo-ansible-inventory --list

In general, Ansible and the validations will be located on the undercloud, because it should have connectivity to all the overcloud nodes is already set up to SSH to them.

$ source ~/stackrc
$ /bin/ --help
Usage: [--help]
                       [--plan <overcloud>]
                       --validation-name <validation_name>

--debug:                      Enable ansible verbose mode (-vvvv connection debugging)
--ansible-default-callback:   Use the 'default' Ansible callback plugin instead of the
                              tripleo-validations custom callback 'validation_output'
--plan:                       Stack name to use for generating the inventory data
--validation-name:            The name of the validation

$ /bin/ --validation-name validation

Example: Verify Undercloud RAM requirements

The Undercloud has a requirement of 16GB RAM. Let’s write a validation that verifies this is indeed the case before deploying anything.

Let’s create playbooks/undercloud-ram.yaml and put some metadata in there:

- hosts: undercloud
      name: Minimum RAM required on the undercloud
      description: >
        Make sure the undercloud has enough RAM.
        - prep
        - pre-introspection

The hosts key will tell which server should the validation run on. The common values are undercloud, overcloud (i.e. all overcloud nodes), controller and compute (i.e. just the controller or the compute nodes).

The name and description metadata will show up in the API and the TripleO UI so make sure to put something meaningful there. The groups metadata applies a tag to the validation and allows to group them together in order to perform group operations, such are running them all in one call.

Now let’s include the Ansible role associated to this validation. Add this under the same indentation as hosts and vars:

- undercloud-ram

Now let’s create the undercloud-ram Ansible role which will contain the necessary task(s) for checking if the Undercloud has the mininum amount of RAM required:

$ cd tripleo-validations
$ ansible-galaxy init --init-path=roles/ undercloud-ram
- undercloud-ram was created successfully

The tree of the new created role should look like:

  ├── defaults
  │   └── main.yml
  ├── meta
  │   └── main.yml
  ├── tasks
  │   └── main.yml
  └── vars
      └── main.yml

Now let’s add an Ansible task to test that it’s all set up properly:

$ cat <<EOF >> roles/undercloud-ram/tasks/main.yml
- name: Test Output
    msg: "Hello World!"

When running it, it should output something like this:

$ /bin/ --validation-name undercloud-ram.yaml --ansible-default-callback

PLAY [undercloud] *********************************************************

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

TASK [undercloud-ram : Test Output] ***************************************
ok: [undercloud] => {
    "msg": "Hello World!"

PLAY RECAP ****************************************************************
undercloud                 : ok=2    changed=0    unreachable=0    failed=0

If you run into an issue where the validation isn’t found, it may be because the script is searching for it in the path where the packaging installs validations. For development, export an environment variable named VALIDATIONS_BASEDIR with the value of base path of your git repo:

$ cd /path/to/git/repo

Writing the full validation code is quite easy in this case because Ansible has done all the hard work for us already. We can use the ansible_memtotal_mb fact to get the amount of RAM (in megabytes) the tested server currently has. For other useful values, run ansible -i /usr/bin/tripleo-ansible-inventory undercloud -m setup.

So, let’s replace the hello world task with a real one:

- name: Verify the RAM requirements
  fail: msg="The RAM on the undercloud node is {{ ansible_memtotal_mb }} MB, the minimal recommended value is 16 GB."
  failed_when: "({{ ansible_memtotal_mb }}) < 16000"

Running this, we see:

TASK: [Verify the RAM requirements] *******************************************
failed: [localhost] => {"failed": true, "failed_when_result": true}
msg: The RAM on the undercloud node is 8778 MB, the minimal recommended value is 16 GB.

Because our Undercloud node really does not have enough RAM. Your mileage may vary.

Either way, the validation works and reports the lack of RAM properly!

failed_when is the real hero here: it evaluates an Ansible expression (e.g. does the node have more than 16 GB of RAM) and fails when it’s evaluated as true.

The fail line right above it lets us print a custom error in case of a failure. If the task succeeds (because we do have enough RAM), nothing will be printed out.

Now, we’re almost done, but there are a few things we can do to make this nicer on everybody.

First, let’s hoist the minimum RAM requirement into a variable. That way we’ll have one place where to change it if we need to and we’ll be able to test the validation better as well!

So, let’s call the variable minimum_ram_gb and set it to 16. Do this in the vars section:

    name: ...
    description: ...
    groups: ...
  minimum_ram_gb: 16

Make sure it’s on the same indentation level as metadata.

Then, update failed_when like this:

failed_when: "({{ ansible_memtotal_mb }}) < {{ minimum_ram_gb|int * 1024 }}"

And fail like so:

fail: msg="The RAM on the undercloud node is {{ ansible_memtotal_mb }} MB, the minimal recommended value is {{ minimum_ram_gb|int * 1024 }} MB."

And re-run it again to be sure it’s still working.

One benefit of using a variable instead of a hardcoded value is that we can now change the value without editing the yaml file!

Let’s do that to test both success and failure cases.

This should succeed but saying the RAM requirement is 1 GB:

.. code-block:: console

ansible-playbook -i /usr/bin/tripleo-ansible-inventory playbooks/undercloud-ram.yaml -e minimum_ram_gb=1

And this should fail by requiring much more RAM than is necessary:

.. code-block:: console

ansible-playbook -i /usr/bin/tripleo-ansible-inventory playbooks/undercloud-ram.yaml -e minimum_ram_gb=128

(the actual values may be different in your configuration – just make sure one is low enough and the other too high)

And that’s it! The validation is now finished and you can start using it in earnest.

Create a new role with automation

The role addition process is also automated using ansible. If ansible is available on the development workstation change directory to the root of the tripleo-validations repository and run the the following command which will perform the basic tasks noted above.

$ cd tripleo-validations/
$ export ANSIBLE_ROLES_PATH="${PWD}/roles"
$ ansible-playbook -i localhost, role-addition.yml -e validation_init_role_name=${NEWROLENAME}

The new role will be created in tripleo-validations/roles/ from a skeleton and one playbook will be added in tripleo-validations/playbooks/.

It will also add a new job entry into the zuul.d/molecule.yaml.

- job:
      - ^roles/${NEWROLENAME}/.*
      - ^tests/prepare-test-host.yml
      - ^ci/playbooks/pre.yml
      - ^ci/playbooks/run.yml
      - ^molecule-requirements.txt
    name: tripleo-validations-centos-8-molecule-${NEWROLENAME}
    parent: tripleo-validations-centos-8-base
      tripleo_validations_role_name: ${NEWROLENAME}

And the job name will be added into the check and gate section at the top of the molecule.yaml file.

- project:
        - tripleo-validations-centos-8-molecule-${NEWROLENAME}
        - tripleo-validations-centos-8-molecule-${NEWROLENAME}

Finally it will add a role documentation file at doc/source/roles/role-${NEWROLENAME}.rst. This file will need to contain a title, a literal include of the defaults yaml and a literal include of the molecule playbook, or playbooks, used to test the role, which is noted as an “example” playbook.

You will now be able to develop your new validation!

Developing your own molecule test(s)

The role addition process will create a default Molecule scenario from the skeleton. By using Molecule, you will be able to test it locally and of course it will be executed during the CI checks.

In your role directory, you will notice a molecule folder which contains a single Scenario called default. Scenarios are the starting point for a lot of powerful functionality that Molecule offers. A scenario is a kind of a test suite for your newly created role.

The Scenario layout

Within the molecule/default folder, you will find those files:

$ ls
molecule.yml  converge.yml  prepare.yml  verify.yml
  • molecule.yml is the central configuration entrypoint for Molecule. With this file, you can configure each tool that Molecule will employ when testing your role.


Tripleo-validations uses a global configuration file for Molecule. This file is located at the repository level (tripleo-validations/.config/molecule/.config.yml). and defines all the default values for all the molecule.yml. By default, the role addition process will produce an empty molecule.yml inheriting this config.yml file. Any key defined in the role molecule.yml file will override values from the config.yml file.

But, if you want to override the default values set in the config.yml file, you will have to redefine them completely in your molecule.yml file. Molecule won’t merge both configuration files and that’s why you will have to redefine them completely.

  • prepare.yml is the playbook file that contains everything you need to include before your test. It could include packages installation, file creation, whatever your need on the instance created by the driver.

  • converge.yml is the playbook file that contains the call for you role. Molecule will invoke this playbook with ansible-playbook and run it against and instance created by the driver.

  • verify.yml is the Ansible file used for testing as Ansible is the default Verifier. This allows you to write specific tests against the state of the container after your role has finished executing.

Inspecting the Global Molecule Configuration file

As mentioned above, tripleo-validations uses a global configuration for Molecule.

# Tripleo-validations uses a shared molecule configuration file to avoid
# repetition. That configuration file is located at the repository level
# ({REPO}/.config/molecule/config.yml) and defines all the default values for
# all the molecule.yml files across all the roles. By default, the role-addition
# process will produce an empty molecule.yml inheriting this config.yml file.
# Any key defined in the role molecule.yml file will override values from this
# config.yml file.
# IMPORTANT: if you want to override the default values set here in this file,
# you will have to redefine them completely in your molecule.yml (at the role
# level) and add your extra configuration!
# For instance, if you need to add an extra package in your CentOS 8 Stream
# container, you will have to add the entire "platforms" key into your
# molecule.yml file and add your package name in the pkg_extras key.
# No merge will happen between your molecule.yml and this config.yml
# files. That's why you will have to redefine them completely.

  name: podman

log: true

  - name: centos
    hostname: centos
    image: centos/centos:stream8
    dockerfile: ../../../../.config/molecule/Dockerfile
    pkg_extras: python*-setuptools python*-pyyaml
      - /etc/ci/
    privileged: true
    environment: &env
      http_proxy: "{{ lookup('env', 'http_proxy') }}"
      https_proxy: "{{ lookup('env', 'https_proxy') }}"
    ulimits: &ulimit
      - host

  name: ansible
            ansible_python_interpreter: /usr/bin/python3
  log: true
    vvv: true
    ANSIBLE_LIBRARY: "${ANSIBLE_LIBRARY:-/usr/share/ansible/plugins/modules}"

    - destroy
    - create
    - prepare
    - converge
    - verify
    - destroy

  name: ansible
  • The Driver provider: podman is the default. Molecule will use the driver to delegate the task of creating instances.

  • The Platforms definitions: Molecule relies on this to know which instances to create, name and to which group each instance belongs. Tripleo-validations uses CentOS 8 Stream image.

  • The Provisioner: Molecule only provides an Ansible provisioner. Ansible manages the life cycle of the instance based on this configuration.

  • The Scenario definition: Molecule relies on this configuration to control the scenario sequence order.

  • The Verifier framework. Molecule uses Ansible by default to provide a way to write specific stat checking tests (such as deployment smoke tests) on the target instance.

Local testing of new roles

Local testing of new roles can be done in two ways:

  • Via the script scripts/run-local-test,

  • or manually by following the procedure described below.

Running molecule tests with the script run-local-test

This script will setup the local work environment to execute tests mimicking what Zuul does on a CentOS 8 machine.


This script makes the assumption the executing user has the ability to escalate privileges and will modify the local system.

To use this script execute the following command.

$ cd tripleo-validations
$ ./scripts/run-local-test ${NEWROLENAME}

When using the run-local-test script, the TRIPLEO_JOB_ANSIBLE_ARGS environment variable can be used to pass arbitrary Ansible arguments. For example, the following shows how to use –skip-tags when testing a role with tags.

$ export TRIPLEO_JOB_ANSIBLE_ARGS="--skip-tags tag_one,tag_two"
$ ./scripts/run-local-test ${ROLENAME}

Running molecule tests manually

Role based testing with molecule can be executed directly from within the role directory.


All tests require Podman for container based testing. If Podman is not available on the local workstation it will need to be installed prior to executing most molecule based tests.


The script bindep-install, in the scripts path, is available and will install all system dependencies.


Each molecule tests are configured to bind mount a read-only volume on the container where the tests are running:

  - /etc/ci/

It is an OpenStack Zuul requirement for detecting if we are on a CI node. Of course, when running your molecule test on your workstation, it is going to fail because you don’t have the empty script in the /etc/ci/ directory. You can workaround this by creating it in your workstation or removing the volume key in the global configuration file for molecule.

$ sudo mkdir -p /etc/ci
$ sudo touch /etc/ci/

Before running basic molecule tests, it is recommended to install all of the python dependencies in a virtual environment.

$ sudo dnf install python3 python3-virtualenv
$ python3 -m virtualenv --system-site-packages "${HOME}/test-python"
$ source "${HOME}/test-python/bin/activate"
(test-python) $ python3 -m pip install "pip>=19.1.1" setuptools bindep --upgrade
(test-python) $ scripts/./bindep-install
(test-python) $ python3 -m pip install -r requirements.txt \
                                       -r test-requirements.txt \
                                       -r molecule-requirements.txt
(test-python) $ ansible-galaxy install -fr ansible-collections-requirements.txt

Now, it is important to install validations-common and tripleo-ansible as dependencies.


validation-common contains Ansible Custom modules needed by tripleo-validations roles. That’s the reason why we will need to clone it beforehand.

Cloning tripleo-ansible project is only necessary in order to run the molecule test(s) for the image_serve role. Otherwise, you won’t probably need it.

$ cd tripleo-validations/
$ for REPO in validations-common tripleo-ansible; do git clone${REPO} roles/roles.galaxy/${REPO}; done

To run a basic molecule test, simply source the ansible-test-env.rc file from the project root, and then execute the following commands.

(test-python) $ source ansible-test-env.rc
(test-python) $ cd roles/${NEWROLENAME}/
(test-python) $ molecule test --all

If a role has more than one scenario, a specific scenario can be specified on the command line. Running specific scenarios will help provide developer feedback faster. To pass-in a scenario use the –scenario-name flag with the name of the desired scenario.

(test-python) $ cd roles/${NEWROLENAME}/
(test-python) $ molecule test --scenario-name ${EXTRA_SCENARIO_NAME}

When debugging molecule tests its sometimes useful to use the –debug flag. This flag will provide extra verbose output about test being executed and running the environment.

(test-python) $ molecule --debug test