Difference between revisions of "Mistral/DSL"

Revision as of 10:12, 5 May 2014

Mistral DSL specification

Version 0.1

Main objects

• Namespace
• Action
• Workflow
• Task
• Trigger

Namespaces

Provides some specific functionality. For example, Nova service provides functionality for VMs management in OpenStack.

Attributes

All attributes are inside main keys of Namespaces - namespaces names

• class - currently we support the following classes: std.http, std.mistral_http, std.echo, std.email, std.ssh, this is an optional attribute
• base-parameters - dictionary depending on type of the namespace, this parameter can be optional. Values of this parameters apply to all actions inside namespace. For example for std.http it can contain url, method, body and headers.
• actions - list of actions provided by this namespace

YAML example:

 Namespaces:
    Nova:
      class: std.http
      parameters:
          method: GET
      actions:
          create-vm:
            ......
          delete-vm:  
            .....

Action

A function provided by services. For example Nova service provides the following actions: create-vm, shutdown-vm

Attributes

• name - string without space, mandatory attribute
• parameters - dictionary, which structured is defined by service type. For REST service it contains url and method.
• task-parameters - dictionary containing parameters which should or could be specified in task
• response - dictionary containing keys 'select' and 'store_as'. Value for 'select' - YAQL expression and means what data action should extract as its result. Value for 'store_as' - string key which should be used for storing in the execution context

YAML example:

 create-vm:
     parameters:
         url: servers
     task-parameters:
         name:
           optional: False
     response:
       select: '$.server.id'
       store_as: vm_id

Workflow

Attributes

• tasks - list of task in this workflow, each task represent some step in worflow
• events - list of events in workflow, e.g. timer or periodic events

YAML example:

 Workflow:
    tasks:
       create-vms:
         .....
       attache-volumes: 
         .....

Task

Represents a step in workflow, for example attaching volume

Attributes

• name - string without space, mandatory attribute
• action - name of action to perform
• requires - list of tasks which should be execute before this tasks, or list of task names as a keys and condition as a value, this is optional parameter
• parameters - list of parameters
• on-success - task which will be scheduled on execution after current task has finished with state 'SUCCESS'
• on-error - task which will be scheduled on execution after current task has finished with state 'ERROR'
• on-finish - task which will be scheduled on execution after current task has finished

YAML example:

 create-vms:
    action: Nova:create-vm
    parameters:
       image_id: 1234
       flavor_id: 42
   requires:
     task2: '$.value2 = 123'
     task4: '$.value4 = 122'
   on-success: task3

Events

By event it is possible to invoke specific task.

Attributes

• name - string without space, mandatory attribute
• type - can be PERIODIC, TIMER, CEILOMETER_ALARM
• tasks - list of tasks which should be execute on event
• parameters - list of parameters, defined by task

YAML example:

 backup-vm:
    type: periodic
    tasks: [create_backup, delete_old_backup] 
    parameters:
       time: 1 0 * * *

Full YAML example:

 Workflow:
 tasks:
   runJob:
     requires:
       createVM: $.vm_ip != null
     action: DemoApp:runJob
     on-success: deleteVM
     on-error: sendJobError
 
   deleteVM:
     action: Nova:deleteVM
     on-finish: end
 
   sendJobError:
     action: std:email
     parameters:
       address: admin@mycompany.com
       subject: Workflow error
       body: Error occurred while running a VM job in execution {$.execution.id}
     on-finish: deleteVM
 
 # Creating a VM and waiting till it is up (an IP address has been assigned).
 
   createVM:
     action: Nova:createVM
     on-success: waitForIP
     on-error: sendCreateVMError
 
   waitForIP:
     action: std:repeat
     parameters:
       task: getIP
       retries: 5
       delay: 3000
       break-on: $.vm_ip != null
     on-finish:
       sendCreateVMError: $.vm_ip = null
     on-error:
       sendCreateVMError 
 
   getIP:
     action: Nova:getIP
 
   sendCreateVMError:
     action: std:email
     parameters:
       address: admin@mycompany.com
       subject: Workflow error
       body: Failed to create a VM in execution {$.execution.id}
     on-finish: end
 
 # Terminal no-op task.
 
   end:
     action: Util:no-op
 
 events:
   runJob:
     type: periodic
     tasks: runJob
     parameters:
       cron-pattern: "*/1 * * * *"
 
 Services:
   Nova:
     type: REST_API
     parameters:
       baseUrl: {$.novaURL}
     actions:
       createVM:
         parameters:
           url: /servers/{$.vm_id}
           method: POST
         response:
           select: $.server.id
           store-as: vm_id
       getIP:
         parameters:
           url: /servers/{$.vm_id}
           method: GET
         response:
           select: $.server.accessIPv4
           store-as: vm_ip 
       deleteVM:
         parameters:
           url: /servers/{$.vm_id}
           method: DELETE
 
 DemoAPP:
   type: MISTRAL_REST_API
   parameters:
     baseUrl: http://{$.vm_ip}:8080/
   actions:
     runJob:
       parameters:
         url: /runJob
         method: GET

Initial execution context

 {
   "novaURL": TBD,
   "imageID": TBD
 }

When a workflow starts Mistral also adds execution information into the context so the context looks like the following:

 {
   "novaURL": TBD,
   "imageID": TBD,
   "execution": {
     "id": "234234",
     "workbook_name" : "my_workbook",
     "project_id": "ghfgsdfasdfasdf"
     "auth_token": "sdfljsdfsdf-234234234",
     "trust_id": "oiretoilkjsdfglkjsdfglkjsdfg"
   }
 }