Use the os-brick library for libvirt volume drivers

https://blueprints.launchpad.net/nova/+spec/use-os-brick-library

Introduce the usage of the os-brick library into Nova. The library will be used inside the libvirt volume drivers for volume discovery and removal for all of the supported protocols. os-brick will also be used to collect the initiator information, which is the connector object, passed to Cinder during for volume attaches.

Problem description

For several OpenStack releases now, there has been duplicate code between Cinder and Nova with respect to volume discovery and removal. Since the Havana release, Cinder has been incubating an embedded library called ‘brick’. The brick library’s purpose was to collect initiator information, discover volumes being attached to a host and to remove volumes already attached. This is essentially the purpose of Nova’s libvirt volume drivers.

Cinder has officially removed the embedded brick library and has switched to using the pypi os-brick library at the start of the Liberty release.

This spec lays out the removal of the duplicate code in Nova’s libvirt volume drivers that exists in the os-brick library.

Use Cases

The main use case for using the os-brick library is when Nova needs to attach or detach a volume. The primary work flow is this, Nova collects the initiator information into a connector object, which gets passed to Cinder to export the volume. Cinder passes back the target information and Nova uses that target information to discover the volume showing up. Instead of using the embedded code in Nova to collect the initiator information, and discover the target volume showing up, Nova will use the os-brick library to do that work. The os-brick library will also be used for volume removal when a Nova needs to detach a volume.

Project Priority

None

Proposed change

First os-brick needs to be a new requirement for Nova. Then rework the libvirt volume drivers to remove their internal code for volume discovery and removal, and replace the code with calls to os-brick Connector objects. Finally, replace the Nova virt/utils code that collects the initiator information that gets passed to Cinder at volume attach time.

Alternatives

Nova can continue to have duplicate code that does the same work as os-brick. This is less than desirable as fixing bugs and adding new features needs to be done in Nova as well as os-brick.

Data model impact

None

REST API impact

None

Security impact

None

Notifications impact

None

Other end user impact

None

Performance Impact

None

Other deployer impact

os-brick will be a required pypi library for Nova.

Developer impact

One of the positive benefits of using this external library is that the Nova team won’t have to maintain the internals of os-brick’s code for volume discovery and removal. os-brick is owned by the Cinder team and any bug fixes and new features added will benefit Nova.

Implementation

Assignee(s)

Who is leading the writing of the code? Or is this a blueprint where you’re throwing it out there to see who picks it up?

If more than one person is working on the implementation, please designate the primary author and contact.

Primary assignee:

walter-boring

Work Items

  • Convert Nova’s code to use os-brick for collecting the initiator information into the connector object.

  • Convert each of the supported libvirt volume drivers to use os-brick Connector objects.

  • Rework the libvirt volume driver unit tests.

Dependencies

Import the os-brick library as a requirement for Nova.

Testing

To test this out correctly, we have to change the unit tests in Nova that look at the internals of volume discovery for iSCSI, FC, etc to test out the os-brick library APIs. Ensure that each of the os-brick Connector objects are loaded correctly for each of the support transports.

We will rely on the os-brick unit tests and releases for volume discovery and removal to work properly, so there is no need to test all of the internals for how iSCSI volume attaches work.

Documentation Impact

We are simply moving the existing functionality of volume discovery and removal from Nova’s embedded libvirt volume drivers to use os-brick. So, there is no doc impact.

History

Back in the Havana time frame we discussed the idea of creating a shared library for doing volume discovery and removal as well as local volume management for Nova and Cinder. The os-brick library is the first step in that direction that solves the volume discover and removal shared code.

Revisions

Release Name

Description

Liberty

Introduced