Alternative Cinder Scheduler Classes¶
Alternative Classes such as filters, host managers, etc. for Cinder, the OpenStack Block Storage service.
The main purpose of this library is to illustrate the broad range of possibilities of the Cinder services provided by their flexible mechanisms.
Originally it was only meant to contain Scheduler related code, hence the name, but now it’s also including API code.
Currently there’s 2 interesting features for the Scheduler, which are the possibility of changing the default provisioning type on volume creation for volumes that don’t specify the type using the provisioning:type extra spec and an alternative calculation of the free space consumption.
Scheduler’s original approach to space consumption by new volumes is conservative to prevent backends from filling up due to a sudden burst of volume creations.
The alternative approach is more aggressive and is adequate for deployments where the workload is well know and a lot of thin volumes could be requested at the same time.
It’s important to notice that even though the Schedulers will be able to understand provisioining:type extra spec it will depend on the backend if this parameter is actually used or not.
Another interesting possibility, added this time at the API level, is having default volume types for specific projects and/or users.
The precedence would be:
1- Source volume type: volume, snapshot, image metadata 2- User’s default volume type 3- Project’s default volume type 4- Cinder configured default_volume_type
User and project default volume types must be defined in Keystone’s DB in the extra field of user and project tables. It is not necessary to define it for all projects and users, if they none is defined Cinder’s default will be used.
The extra field is a JSON string and may already contain extra information like an email address.
The key used to define the default volume types is default_vol_type and its value can be an UUID or a name.
Since there is no CRUD REST API available in Keystone for custom values in the extra field we’ll need to change this manually in the DB.
- Free software: Apache Software License 2.0
- Documentation: https://alt-cinder-sch.readthedocs.io.
- Can default capacity calculations to thin or thick.
- Less conservative approach to free space consumption calculations.
- Per project and/or user default volume types.
First we’ll need to have the package installed:
# pip install alt_cinder-sch
For Cinder’s scheduler features we’ll have to change the configuration to use the package:
scheduler_host_manager = alt_cinder_sch.host_managers.HostManagerThin scheduler_default_filters = AvailabilityZoneFilter,AltCapacityFilter,CapabilitiesFilter scheduler_driver = alt_cinder_sch.scheduler_drivers.FilterScheduler
And finally restart scheduler services.
For Cinder’s API feature the Cinder configuration is just:
volume_api_class = alt_cinder_sch.api.DefaultVolumeTypeAPI
As well as changing Keystone’s user and project tables.