Implement Mistral resources

https://blueprints.launchpad.net/heat/+spec/mistral-resources-for-heat

Add support for Mistral resources which will allow to create and execute workflows.

Problem description

Heat doesn’t support Mistral resources currently.

Mistral is a task management service, also known as Workflow as a Service. Resources, which will be added to Heat, add new possibilities:

  • Workflows, which contains different tasks for execution.
  • Actions, which are a particular instructions associated with a tasks that needs to be performed once tasks dependencies are satisfied.
  • CronTriggers, which make possible to run workflows according to specific rules: periodically setting a cron pattern or on external events like Ceilometer alarm.
  • Executions, which allows to execute given Workflows.

Proposed change

Mistral resources are not integrated, so they will be added to contrib directory. Mistral client plugin will be added for communication with Mistral, which has his own requirements. Following resources will be added with next syntax:

Add the OS::Mistral::Workflow resource, like this:

resources:
 workflow:
   type: OS::Mistral::Workflow
   properties:
     definition: |
       workflow_name:
         type: String
         description: String
         input: [Value, Value, ...]
         output: { ... }
         on-success: [Value, Value, ...]
         on-error: [Value, Value, ...]
         on-complete: [Value, Value, ...]
         policies: { ... }
         tasks: { ... }
     input: { ... }

Where definition specifying rely on Mistral DSL v2.

Add the OS::Mistral::CronTrigger resource, like this:

resources:
  cronTrigger:
    type: OS::Mistral::CronTrigger
    properties:
      name: my_cron_trigger
      pattern: 1 0 * * *
      workflow:
        name: String
        input: { ... }

There is some use cases, which should be described:

  1. To create and execute workflow follow next steps: at first we create template with OS::Mistral::Workflow:

    heat_template_version: 2013-05-23
    resources:
      workflow:
        type: OS::Mistral::Workflow
        properties:
          definition: |
            test:
              type: direct
              tasks:
                hello:
                  action: std.echo output='Hello'
                  publish:
                    result: $
    

    When stack will created, to execute workflow run next command:

    heat resource-signal stack_name workflow_name \
        -D 'Json-type execution input'

    Execution state will be available in ‘executions’ attribute as a dict.

  2. Compatibility with Ceilometer alarms, i.e. using webhook url for workflow executing:

    heat_template_version: 2013-05-23
    resources:
      workflow:
        type: OS::Mistral::Workflow
        properties:
          definition: |
            test:
              type: direct
              tasks:
                alarm_hello:
                  action: std.echo output='Alarm!'
                  publish:
                    result: $
      alarm:
        type: OS::Ceilometer::Alarm
        properties:
            alarm:
              type: OS::Ceilometer::Alarm
              properties:
                meter_name: cpu_util
                statistic: avg
                period: 60
                evaluation_periods: 1
                threshold: 0
                alarm_actions:
                  - { get_attr: [workflow, alarm_url] }
                comparison_operator: ge
    outputs:
      executions:
        value: { get_attr: [workflow, executions] }
      workflows:
        value: { get_attr: [workflow, available_workflows] }
    

    In the template, described above, workflow will begin execute when alarm will goes to the state ‘alarm’. Output ‘execution’ contain dict with info about all executions, which belong to the workflow. Output ‘workflows’ contain dict with all workflows’ names that belong to the workflow, e.g. {‘test’: ‘stack_name.workflow.test’}.

  3. Using cron trigger in template. There is the definition named ‘wfdef.yaml’:

    version: 2.0
      create_vm:
        type: direct
        input:
          - vm_name
          - image_ref
          - flavor_ref
        output:
          vm_id: $.vm_id
        tasks:
          create_server:
            action: >
              nova.servers_create name={$.vm_name} image={$.image_ref}
              flavor={$.flavor_ref}
            publish:
              vm_id: $.id
            on-success:
              - check_server_exists
          check_server_exists:
            action: nova.servers_get server={$.vm_id}
            publish:
              server_exists: True
            on-success:
              - wait_instance
          wait_instance:
            action: nova.servers_find id={$.vm_id} status='ACTIVE'
            policies:
              retry:
                delay: 5
                count: 15
    

    This definition will be used in template, which also have cron trigger resource:

    heat_template_version: 2013-05-23
    resources:
      workflow:
        type: OS::Mistral::Workflow
        properties:
          definition: { get_file: wfdef.yaml }
          input:
            vm_name: test
            image_ref: some_image_id
            flavor_ref: some_flavor_id
    
      cron_trigger:
        type: OS::Mistral::CronTrigger
        properties:
          name: test_trigger
          pattern: 1 0 * * *
          workflow: { get_attr: [workflow, available_workflows, create_vm]}
    

    Need to note, that name is optional attribute.

Alternatives

None

Implementation

Assignee(s)

Primary assignee:
<prazumovsky>
Assisted by:
<tlashchova>

Milestones

Target Milestone for completion:
Kilo-2

Work Items

  • Add Mistral client plugin for Heat
  • Add Mistral workflow resource
  • Add Mistral cron trigger resource

Dependencies

None

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