Refactor execute-mistral action

Refactor execute-mistral action

launchpad blueprint: https://blueprints.launchpad.net/vitrage/+spec/refactor-execute-mistral-definition

The definition of the execute-mistral action should be changed, to better support the integration of Vitrage and Mistral.

Problem description

With the current execute-mistral action definition, it is possible to pass string values to the Mistral workflow, but not dynamic attributes like the id or ip address of the instance that was matched in the template condition. We should enhance the template language to support passing dynamic attributes to Mistral.

Another issue is that the structure of the action definition should be changed. In the current structure, optional input parameters to the workflow appear on the same level as the ‘workflow’ property, which is a mandatory part of the action definition:

- action:
    action_type: execute_mistral
    properties:
      workflow: evacuate_host
      timeout: 10
      force: false

Instead, we should gather all optional parameters (timeout and force) under an ‘input’ section.

Proposed change

The first part of the change is to create a new ‘input’ section, under which all input parameters of the workflow should be placed. A new versioning mechanism should be introduced to Vitrage templates, to allow validating and loading of both the old format and the new format. At the first stage both formats will be supported, but in a version or two we should deprecate the old format.

The second part is to define a way to describe which attribute of a specific entity should be passed to the workflow. The suggested solution is to use a syntax that is similar to the HOT template.

We will introduce a get_attr() function with the following parameters:

  • resource template_id: the id of the resource inside the template. Note that the resource must be part of the condition.
  • attribute: the name of the attribute to use. The attribute will be taken from the resource vertex in the graph, if the condition is met.
- scenario:
    condition: host_down_alarm_on_host
    actions:
      - action:
          action_type: execute_mistral
          properties:
            workflow: evacuate_host
            input:
              host_id: get_attr(host, "id")
              host_ip_addr: get_attr(host, "ip_address")
              timeout: 10
              force: false

Alternatives

One alternative is to replace the get_attr with a shorter syntax. In this case, we will refer to an entity attribute by the entity template-id and the attribute name. For example, host.ip_address will mark the ip_address attribute of the instance.

The example above will look like:

- action:
    action_type: execute_mistral
    properties:
      workflow: evacuate_host
      input:
        host_id: host.id
        host_ip_addr: host.ip_address
        timeout: 10
        force: false

This looks much nicer, but has two main disadvantages:

  • It is not clear, just by looking at the template, that this is a reference to an attribute. What if the user wants to pass a string which is “host.id”?
  • It is less generic. On the other hand, if we add get_attr as a function syntax, we will be able to add other functions in the future with a similar syntax.

Data model impact

None

REST API impact

None

Versioning impact

The suggested change is not backward-compatible with Pike. Vitrage templates should be enhanced to support versioning, and both the old version and the new one should be supported for now.

Other end user impact

None

Deployer impact

None

Developer impact

None

Horizon impact

None

Implementation

Assignee(s)

Primary assignee:
ifat-afek

Work Items

  • Support versioning in Vitrage templates. Allow per-version validators and loaders for specific actions.
  • Move optional input parameters under ‘input’ section
  • Support get_attr

Dependencies

None

Testing

The implementation will be covered by unit tests and tempest tests.

Documentation Impact

The changes in the action definition should be documented

Creative Commons Attribution 3.0 License

Except where otherwise noted, this document is licensed under Creative Commons Attribution 3.0 License. See all OpenStack Legal Documents.

vitrage-specs