Mistral/DSLv1

Mistral DSL specification

Version 0.1 (NOT SUPPORTED SINCE April 2015)

Main objects

• Namespace
• Action
• Workflow
• Task
• Trigger

Namespaces

Contains a list of namespaces grouping custom (ad-hoc) actions. For example, it's possible to create namespace "Nova" that would provide actions "createVM", "deleteVM" and similar for VM management in OpenStack.

Attributes

All attributes are inside main keys of Namespaces - namespaces names. Attributes of an individual namespace are:

• class - currently Mistral supports the following action classes out of the box: 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 is optional. Values of these parameters apply to all actions inside the 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
    base-parameters:
      method: GET
    actions:
      create-vm:
      ......
      delete-vm:  
      .....

Action

A function provided by specific namespace.

Attributes

• name - action name (string without space, mandatory attribute).
• base-parameters - dictionary whose structure is defined by action class (or namespace class if defined). For std.http class it contains url, method, body and headers according to HTTP protocol specification.
• parameters - list containing parameter names which should or could be specified in task. This attribute is optional and used only for documenting purposes.
• output - dictionary-transformer for action output to send this output next to task. Keys of this dictionary will be included in task result, values are pure YAQL or inline YAQL expressions per key which define how the specific output should be retrieved from raw output (from action). See more about YAQL at https://pypi.python.org/pypi/yaql/0.3

YAML example:

create-vm:
  base-parameters:
    url: servers
  parameters:
    - name
    - server_name  
  output:
    vm_id: $.content.server.id

Workflow

Attributes

• tasks - list of tasks in this workflow, each task represents a computational step in the workflow.

YAML example:

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

Task

Represents a step in workflow, for example creating the VM

Attributes

• 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 - actual parameters for the task, each value can be either some number, string etc, or YAQL expression to retrieve value from task context
• 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-vm:
  action: Nova.create-vm
  parameters:
    image_id: $.image_id
    flavor_id: 42
  requires:
    task2: '$.value2 = 123'
    task4: '$.value4 = 122'
  on-success: task3

Triggers

Using triggers it is possible to run workflows according to specific rules: periodically setting a cron (http://en.wikipedia.org/wiki/Cron) pattern or on external events like ceilometer alarm.

Attributes

• type - can be PERIODIC, CEILOMETER_ALARM
• tasks - list of tasks which should be execute on trigger
• parameters - list of task parameters

YAML example:

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

Full YAML example:

This example requires the following properties provided in execution context:

1. - nova_url ## url to Nova service, e.g. http://0.0.0.0:8774/v3
2. - server_name ## Name you want to give to new instance
3. - image_id ## image id from Glance service
4. - flavor_id ## flavor id - type of instance hardware
5. - ssh_username ## username of your VM
6. - ssh_password ## password to your VM
7. - admin_email ## email address to send notifications to
8. - from_email ## email address to send notifications from
9. - smtp_server ## SMTP server to use for sending emails (e.g. smtp.gmail.com:587)
10. - smtp_password ## password to connect to SMTP server

Namespaces:
 Nova:
   # Nova actions for creating VM, retrieving IP and VM deleting.
   class: std.http
   actions:
     createVM:
       base-parameters:
         url: '{$.nova_url}/{$.project_id}/servers'
         method: POST
         headers:
           X-Auth-Token: $.auth_token
           Content-Type: application/json
         body:
           server:
             name: $.server_name
             imageRef: $.image_id
             flavorRef: $.flavor_id
       output:
         vm_id: $.content.server.id
 
     getIP:
       base-parameters:
         url: '{$.nova_url}/{$.project_id}/servers/{$.vm_id}'
         method: GET
         headers:
           X-Auth-Token: $.auth_token
       output:
         vm_ip: "$.content.server.addresses.novanetwork.where($.'OS-EXT-IPS:type' = 'floating')[0].addr"
 
     deleteVM:
       base-parameters:
         url: '{$.nova_url}/{$.project_id}/servers/{$.vm_id}'
         method: DELETE
         headers:
           X-Auth-Token: $.auth_token
       output:
         status: $.status
 
 Server:
   actions:
     # HTTP request to the server.
     calcSumm:
       class: std.http
       base-parameters:
         url: 'http://{$.vm_ip}:5000/summ'
         method: POST
         body:
           arguments: $.arguments
       output:
         summ_result: $.content.result
 
 Ssh:
   class: std.ssh
   base-parameters:
     host: $.vm_ip
     username: $.username
     password: $.password
   actions:
     # Simple SSH command.
     waitSSH:
       base-parameters:
         cmd: 'ls -l'
 
     # SSH command to run the server.
     runServer:
       base-parameters:
         cmd: 'nohup python ~/web_app.py > web_app.log &'
 
Workflow:
 tasks:
   # Create a VM (request to Nova).
   createVM:
     action: Nova.createVM
     parameters:
       server_name: $.server_name
       image_id: $.image_id
       flavor_id: $.flavor_id
       nova_url: $.nova_url
       project_id: $.project_id
       auth_token: $.auth_token
     publish:
       vm_id: vm_id
     on-success: waitForIP
     on-error: sendCreateVMError
 
   # Wait till the VM is assigned with IP address (request to Nova).
   waitForIP:
     action: Nova.getIP
     retry:
       count: 10
       delay: 10
     publish:
       vm_ip: vm_ip
     parameters:
       nova_url: $.nova_url
       project_id: $.project_id
       auth_token: $.auth_token
       vm_id: $.vm_id
     on-success: waitSSH
     on-error: sendCreateVMError
 
   # Wait till operating system on the VM is up (SSH command).
   waitSSH:
     action: Ssh.waitSSH
     retry:
       count: 10
       delay: 10
     parameters:
       username: $.ssh_username
       password: $.ssh_password
       vm_ip: $.vm_ip
     on-success: runServer
     on-error: sendCreateVMError
 
   # When SSH is up, we are able to run the server on VM (SSH command).
   runServer:
     action: Ssh.runServer
     parameters:
       vm_ip: $.vm_ip
       username: $.ssh_username
       password: $.ssh_password
     on-success: calcSumm
     on-error: sendCreateVMError
 
   # Send HTTP request on server and calc the result.
   calcSumm:
     action: Server.calcSumm
     retry:
       count: 10
       delay: 1
     parameters:
       arguments:
         - 32
         - 45
         - 23
       vm_ip: $.vm_ip
     publish:
       result: summ_result
     on-finish: sendResultEmail
 
   # In case of createVM error send e-mail with error message.
   sendResultEmail:
     action: std.email
     parameters:
       params:
         to: [$.admin_email]
         subject: Workflow result
         body: |
           Workflow result of execution {$.__execution.id} is {$.result}
 
           -- Thanks, Mistral Team.
       settings:
         smtp_server: $.smtp_server
         from: $.from_email
         password: $.smtp_password
     on-finish: deleteVM
 
   # In case of createVM error send e-mail with error message.
   sendCreateVMError:
     action: std.email
     parameters:
       params:
         to: [$.admin_email]
         subject: Workflow error
         body: |
           Failed to create a VM in execution {$.__execution.id}
 
           -- Thanks, Mistral Team.
       settings:
         smtp_server: $.smtp_server
         from: $.from_email
         password: $.smtp_password
     on-finish: deleteVM
 
   # Destroy the VM (request to Nova).
   deleteVM:
     action: Nova.deleteVM
     parameters:
       nova_url: $.nova_url
       project_id: $.project_id
       auth_token: $.auth_token
       vm_id: $.vm_id

Initial execution context

 {
   "nova_url": <nova_url>,
   "image_id": <image_id>,
   "flavor_id": <flavor_id>,
   "server_name": <server_name>,
   "ssh_username": <ssh_username>,
   "ssh_password": <ssh_password>,
   "admin_email": <admin_email>,
   "from_email": <from_email>,
   "smtp_server": <smtp_server>,
   "smtp_password": <smtp_password>,
 }

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

 {
   "nova_url": TBD,
   "image_id": TBD,
   "image_id": <image_id>,
   "flavor_id": <flavor_id>,
   "server_name": <server_name>,
   "ssh_username": <ssh_username>,
   "ssh_password": <ssh_password>,
   "admin_email": <admin_email>,
   "from_email": <from_email>,
   "smtp_server": <smtp_server>,
   "smtp_password": <smtp_password>,
   "__execution": {
     "id": "234234",
     "workbook_name" : "my_workbook",
     "project_id": "ghfgsdfasdfasdf"
     "auth_token": "sdfljsdfsdf-234234234",
     "trust_id": "oiretoilkjsdfglkjsdfglkjsdfg"
   }
 }