Mistral Actions Library

Launchpad blueprint:


This specification outlines a proposal to move the OpenStack actions to mistral-extra and define a process for accepting other third party actions in mistral-extra.

Problem description

Mistral ships with a set of standard generic actions and a set of actions specific to OpenStack. The OpenStack actions help improve the utility of Mistral but including them in Mistral itself raises a number of limitations.

  • Some users won’t want OpenStack actions. (i.e. Mistral running outside OpenStack).

  • Some users will only want specific OpenStack actions. (i.e. their deployment only includes certain OpenStack projects).

  • OpenStack actions can easily become out of date as the OpenStack clients can evolve quickly. Releases to these actions require full Mistral releases.

The OpenStack actions make Mistral much more useful in OpenStack environments but there isn’t a clear place to collect or develop other Mistral actions. Without a wider set of actions that integrate with other services and projects Mistral is unlikely to become used more widely.

Use Cases

  • As an administrator and deployer I want control over the actions included with Mistral.

  • As a developer I want a clear place to contribute to actions and add support for third party actions.

  • As an end user I want my workflows to have access to a library of actions that allow my workflows to do more without having to create custom actions.

Proposed change

This specification proposes moving the current OpenStack actions to the mistral-extra repo, which can be then referred to as the Mistral actions library. This repository will depend on mistral-lib, as being developed under the custom actions API spec.

mistral-extra will contain a Python namespace for all the OpenStack actions, this will likely be mistral_extra.openstack. The action names will remain as they are now to maintain backwards compatability. It will also allow other actions to be added to this project if they meet the requirements.

For an action to be considered for mistral-extra it should be generic and useful for a wide range of users and not specific to one user or project. There should also be a way to automate the testing of this action to verify that it continues to work over time. Without the ability to do an integration test the actions will become impossible to maintain as the library grows. Generally useful actions are also candidates to be included in Mistral itself with the other std.* actions.

A configuration file will be added that allows users to specify which actions they want to include. By default this config will match the existing behaviour and include all OpenStack actions, but other actions will need to be enabled for each project.


Alternatively we could continue storing the actions in Mistral and third party actions could be developed outside of Mistral entirely. This may work, but it would make it much harder to grow a cohesive library that is easy to use.

Data model impact

No data model changes are required.

REST API impact

No API changes are required.

Python API

The mistral-extra repository will also provide a stable Python API that can be used by action developers as a library. This will allow them to access the OpenStack actions and extend or customise them. The API is still to be determined but usage will likely look something like this.

from mistral_extra import openstack

class CustomNovaAction(openstack.NovaAction):

    def run(self, context):

        nova_client = self.get_client(context)
        # do something custom and return

Access to the Python clients for OpenStack projects will also be possible. This will allow custom action developers to easily consume multiple OpenStack clients.

from mistral_extra import openstack
from mistral_lib import actions

class CustomAction(actions.Action):

    def run(self, context):

        nova_client = openstack.NovaAction.get_client(context)
        glance_client = openstack.GlanceAction.get_client(context)

End user impact

Users will primarily interact with the feature by customising the mistral-extra config file. This will need to be documented.

Performance Impact

No performance impact.

Deployer impact

No additional steps will be required by default for deployers. However, they will have greater control of their deployment and which actions are included and available to users.



Primary assignee:


Other contributors:


Work Items

  • Copy OpenStack actions to mistral-extra

  • Package and release mistral-extra and update Mistral to depend on it

  • Remove OpenStack actions from mistral

  • Update the documentation to reflect the configuration of mistral-lib



This will reduce the testing burden on the main Mistral repository. However, additional test cases will be needed for mistral-extra. It may also be wise to setup a periodic test to verify that a recent version of Mistral master still works with mistral-extra.