Replace Mistral with Ansible

Include the URL of your launchpad blueprint:

https://blueprints.launchpad.net/tripleo/+spec/tripleo-mistral-to-ansible

The goal of this proposal is to replace Mistral in TripleO with Ansible playbooks.

Problem Description

Mistral was originally added to take the place of an “API” and provide common logic for tripleoclient and TripleO UI. After the TripleO UI was removed, the only consumer of Mistral is tripleoclient. This means that Mistral now adds unnecessary overhead and complexity.

Proposed Change

Overview

Remove Mistral from the TripleO undercloud and convert all Mistral workbooks, workflows and actions to Ansible playbooks within tripleo-ansible. tripleoclient will then be updated to execute the Ansible playbooks rather than the Mistral workflows.

Alternatives

The only other alternative candidate is to keep using Mistral and accept the complexity and reinvest in the project.

Security Impact

  • As the code will be re-writing Mistral workflows that currently deal with passwords, tokens and secrets we will need to be careful. However the logic should be largely the same.

  • With the eventual removal of Mistral and Zaqar two complex systems can be removed which will reduce the surface area for security issues.

  • The new Ansible playbooks will only use the undercloud OpenStack APIs, therefore they shouldn’t create a new attack vector.

Upgrade Impact

  • Upgrades will need to remove Mistral services and make sure the Ansible playbooks are in place.

  • Older versions of tripleoclient will no longer work with the undercloud as they will expect Mistral to be present.

  • Most of the data in Mistral is ephemeral, but some longer term data is stored in Mistral environments. This data will likely be moved to Swift.

Other End User Impact

The output of CLI commands will change format. For example, the Mistral workflow ID will no longer be included and other Ansible specific output will be included. Where possible we will favour streaming Ansible output to the user, making tripleoclient very light and transparent.

Some CLI commands, such as introspection will need to fundamentally change their output. Currently they send real time updates and progress to the client with Zaqar. Despite moving the execution locally, we are unable to easily get messages from a Ansible playbook while it is running. This means the user may need to wait a long time before they get any feedback.

Performance Impact

There is no expected performance impact as the internal logic should be largely the same. However, the Ansible playbooks will be executed where the user runs the CLI rather than by the Mistral server. This could then be slower or faster depending on the resources available to the machine and the network connection to the undercloud.

The undercloud itself should have more resources available since it wont be running Mistral or Zaqar.

Other Deployer Impact

If anyone is using the Mistral workflows directly, they will stop working. We currently don’t know of any users doing this and it was never documented.

Developer Impact

Developers will need to contribute to Ansible playbooks instead of Mistral workflows. As the pool of developers that know Ansible is larger than those that know Mistral this should make development easier. Ansible contributions will likely expect unit/functional tests.

Implementation

Assignee(s)

Primary assignee:

d0ugal

Other contributors:

  • apetrich

  • ekultails

  • sshnaidm

  • cloudnull

Work Items

Storyboard is being used to track this work:

https://storyboard.openstack.org/#!/board/208

  • Migrate the Mistral workflows to Ansible playbooks.

  • Migrate or replace custom Mistral actions to Ansible native components.

  • Remove Mistral and Zaqar.

  • Update documentation specific to Mistral.

  • Extend our auto-documentation plugin to support playbooks within tripleo-ansible. This will allow us to generate API documentation for all playbooks committed to tripleo-ansible, which will include our new cli prefixed playbooks.

Converting Mistral Workflows to Ansible

For each Mistral workflow the following steps need to be taken to port them to Ansible.

  • Re-write the Mistral workflow logic in Ansible, reusing the Mistral Python actions where appropriate.

  • Update python-tripleoclient to use the new Ansible playbooks. It should prefer showing the native Ansible output rather than attempting to replicate the previous output.

  • The Workflows and related code should be deleted from tripleo-common.

A complete example can be seen for the openstack undercloud backup command.

Dependencies

None

Testing

Since this change will largely be a re-working of existing code the changes will be tested by the existing CI coverage. This should be improved and expanded as is needed.

Documentation Impact

Any references to Mistral will need to be updated to point to the new ansible playbook.