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