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  • Launchpad Entry: QonoS scheduling service
  • Created: 3 May 2013
  • Contributors: Alex Meade, Eddie Sheffield, Andrew Melton, Iccha Sethi, Nikhil Komawar, Brian Rosmaita


This document describes the design and API of QonoS, a distributed high-availability scheduling service that has been implemented for the cloud[1]. QonoS is currently used as the scheduling component of a scheduled images service that is invoked by a Nova extension, so many of the examples in this document discuss that use case.

Service responsibilities include:

  • Create scheduled tasks
  • Perform scheduled tasks
  • Handle rescheduling failed jobs
  • Maintain persistent schedules

QonoS was designed to work with OpenStack and uses OpenStack common components.

Conceptual Overview

The system consists of:

  • an API
  • a database
  • one or more schedulers, and
  • one or more workers.

The API handles communication, both external requests and internal communication. It creates the schedule for a request and stores it in the database.

The scheduler examines schedules and creates jobs.

A job describes a task that must be performed.

A worker performs a task. It obtains a task by polling the API and picking up the first task it is capable of handling.

Job Lifecycle

Jobs have the following statuses:

  • queued : the job is ready to be processed by a worker
  • processing : the job has been picked up by a worker
  • done : the worker processing this job has decided that the job has been successfully completed
  • timeout : the worker processing this job has decided the job is taking too long and has stopped processing it. A job in this state can be picked up by another worker.
  • error : the worker notes that something went wrong, but the job could be retried
  • canceled : the worker decides that the job can't be done and should not be retried

Job Timeouts

There are two kinds of timeouts:

  • hard timeout: once reached, the job is no longer available for retries
  • soft timeout: is renewed by the worker, indicates that the worker is still doing the task (similar to a heartbeat)

Job Failures

Job failures are reported as job faults and stored in the database.


Address or remove?


Address or remove?

Overall System Diagram

Qonos Diagram.png



  • Schedule
    • the general description of what the service will do
    • looks something like
  "tenant_id" : <tenantId>,
  "schedule_id" : <scheduleId>,
  "job_type" : <keyword>,
  "metadata" : {
    // all the information for this job_type
    "key" : "value"
   "schedule" : <the schedule info, exact format TBD>


CRUD for schedules

Create Schedule
POST <version>/schedules
            "tenant": "tenant_username",
            "action": "snapshot",
            "minute": 30,
            "hour": 2,
            "day": 3,
            "day_of_week": 5,
            "day_of_month": 23,
                "instance_id": "some_uuid",
                "retention": "3"
List schedules
GET <version>/schedules
            # schedule as above
            # schedule as above
Query filters
  • next_run_after - only list schedules with next_run value >= this value
  • next_run_before - only list schedules with next_run value <= this value

List schedules which start in the next five minutes

GET <version>/schedules?next_run_after={Current_DateTime}&next_run_before={Current_DateTime+5_Minutes}
GET <version>/schedules?next_run_after=2012-05-16T15:27:36Z&next_run_before=2012-05-16T15:32:36Z
Get a specific schedule
GET /v1/schedules/{id}
Update a schedule
PUT <version>/schedules/{id}
            "minute": 45,
            "hour": 3
Delete a schedule
DELETE <version>/schedules/{id}

CRUD for jobs

Create job from schedule
POST <version>/jobs
    {"job": {"schedule_id": "some_uuid"}}

The action, tenant_id, and metadata gets copied from the schedule to the job.

Get a specific job
GET <version>/jobs/{id}
        "id": "{some_uuid}",
        "created_at": "{DateTime}",
        "updated_at": "{DateTime}",
        "schedule_id": "{some_uuid}",
        "worker_id": "{some_uuid}",
        "tenant": "tenant_username",
        "action": "snapshot",
        "status": "queued",
        "retry_count": 0,
        "hard_timeout": "{DateTime}",
        "timeout": "{DateTime}",

            "key1": "value1",
            "key2", "value2"
List current jobs
GET <version>/jobs
            # job as above
            # job as above
Update status of a job
PUT <version>/jobs/{id}/status
        "status": "some_status",
        "timeout": "{datetime of next timeout}" (optional)
        "error_message":"some message" (optional)

NOTE: The error_message field is only looked for if the status is ERROR. In the event of an ERROR status, an entry is created in the job_faults table capturing as much info as possible from the job. If an error_message is provided, it is included in the job fault entry.

Delete(finish) a specific job
DELETE <version>/jobs/{id}


Set schedule/job metadata
PUT <version>/schedules/{id}/metadata
PUT <version>/jobs/{id}/metadata

Note: The resulting metadata for a schedule/job will exactly match what is provided.

        "each": "someval",
        "meta": "someval",
        "key": "someval",
List all metadata for a schedule/job
GET <version>/schedules/{id}/metadata
GET <version>/jobs/{id}/metadata
        "instance_id": "some_uuid",
        "retention": "3"

Worker related

GET /v1/workers
GET /v1/workers/{workerId}
GET /v1/workers/{workerId}/jobs/next
 * return job info, format TBD
POST /v1/workers
 * returns a workerId, is done when a worker is instantiated, allows the system to keep track of the worker
DELETE /v1/workers/{workerId}
 * should be called by the worker if/when it's safely taken down


The service shall consist of a set of apis, worker nodes, and a DB.

API - Provides a RESTful interface for adding schedules to the DB

Worker - References schedules in the DB to schedule and perform jobs

DB - Tracks schedules and currently executing jobs


  • schedules
  • jobs
  • job faults
    • must be useful!


Typical flow of the system is as follows.

  1. User makes request to Nova extension
  2. Nova extension passes request to API
  3. API picks time of day to schedule
  4. Adds schedule entry to DB
  5. Worker polls DB for schedules needing action
  6. Worker creates job entry in DB
  7. Worker initiates image snapshot
  8. Worker waits for completion while updating 'last_touched' field in the job table (to indicate the Worker has not died)
  9. Worker updates DB to show the job has been completed
  10. Worker polls until a schedule needs action

Edge cases:

Worker dies in middle of job:

  • A different worker will see the job has not been updated in awhile and take over, performing any cleanup it can.
  • Jobs contain information of where they left off and what image they were working on (this allows a job whose worker died in the middle of an upload to be resumed)

Image upload fails

  • Retry a certain number of times, afterwards leave image in error state

Instance no longer exists

  • Remove schedule for instance

Code Repository


  1. QonoS was first described in https://wiki.openstack.org/wiki/Scheduled-images-service (29 October 2012).