Support simple json format in os::mistral::workflow handle signal

Currently the resource os::mistral::workflow expects a specific json format when it is signaled (either using the alarm-url or the resource-signal API call). Since external systems don’t always enable the user to change the body of the request they send, the workflows are not able to use the information sent by these systems.

Problem description

When signaling the OS::Mistral::Workflow resource, from an external system, or even from ceilometer, the signaling request may have a predefined body, which is not compatible with the json format expected by the workflow resource. The os::mistral::workflow expects the body to be in this format:


however, ceilometer, for example, sends this body in the request:

     "severity": "low",
     "alarm_name": "my-alarm",
     "current": "insufficient data",
     "alarm_id": "895fe8c8-3a6e-48bf-b557-eede3e7f4bbd",
     "reason": "1 datapoints are unknown",
     "reason_data": {
           "count": 1,
           "most_recent": null,
           "type": "threshold",
           "disposition": "unknown"
     "previous": "ok"

This causes the problem that the workflow can’t use the information in the request body.

Proposed change

The suggested change is to enable the workflow resource to parse the request body as a simple json map, where each key will be treated as an input value.

This change will not break backward compatibility as the user can choose how the body would be parsed in the stack template.

The proposal is to add a new property “use_request_body_as_input” to os::mistral::workflow, when this property is defined in the template and is True, then the parsing of the signal request body will be parsed as a simple json map. If the property is not defined or defined to False, the body will be parsed as it always has (expecting the keys “input” and “params”).

Since the external systems using this signal send a predefined request, we can assume that they are unaware of the fact they are signaling a workflow, and so, they don’t have the need to pass “params” which is mistral workflow specific. The params can be defined in the stack template but overriding them using the request, will not be enabled in this case.

For example in order for a workflow resource to use information from a ceilometer alarm, it’s definition in the stack template would be something like this:

    type: OS::Mistral::Workflow
      use_request_body_as_input: True
        current: !!null
        alarm_id: !!null
        reason: !!null
        previous: !!null
        severity: !!null
        alarm_name: !!null
        reason_data: !!null




When the resource is being signaled it will check for the existence of the “use_request_body_as_input” property and based on its definition, it will parse the request body, to find the appropriate input values.

It is worth noting that if the workflow resource is created with the property “use_request_body_as_input” set to True, then the workflow “params” cannot be passed to the request.


Primary assignee:


Target Milestone for completion:

Work Items

  1. Change workflow resource to parse the request in the appropriate way based on resource definition.
  2. Add tests to see that both old and new functionality are working.