Scheduled-images-service

• Launchpad Entry: GlanceSpec:scheduled-iamges-service
• Created: 29 Oct 2012
• Contributors: Alex Meade, Eddie Sheffield

Summary

This blueprint introduces a new service and Nova API extension for scheduling daily snapshots of an instance.

Service responsibilities include:

• Allow creation, deletion, and listing of schedules
• Determine specific schedules with regards to load balancing
• Handle rescheduling failed jobs
• Maintain persistant schedules
• Removal of images outside of rotation count

Design

API Extension

Create Backup Schedule POST /servers/<id>/backup_schedule

{ "rotation": INT }

Rotation: Specifies the number of recent backups to keep for an instance. If a schedule already exists for an instance, it is overridden.

Delete Backup Schedule DELETE /servers/<id>/backup_schedule

Show Backup Schedule GET /servers/<id>/backup_schedule

Response Body: {

"instance": <UUID>,
"rotation": INT,

}

List All Backup Schedules of a Tenant GET /servers/backup_schedules

Response Body: [ {

"instance": <UUID>,
"rotation": INT,

}, ]

Service

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

Implementation

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

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