Brick fetch volume paths API

Brick fetch volume paths API

https://blueprints.launchpad.net/cinder/+spec/brick-fetch-paths

The Brick (os-brick) library currently has the knowledge of how to discover and remove volumes from the scsi subsystem on a host. Every connector object has the ability to return a list of existing paths on the system for a given volume, as well as the location where those volume paths live. This spec’s purpose is to detail a formal API for fetching the existing paths for a volume, as well as the search path, and the list of all existing volumes for a connector. The purpose of this is to allow the verification of volume paths after attachment, as well as verification of a volume being removed after detachment. Once we have this API in place, then it’s possible to automate the verification of attaches and detaches for complex operations.

Problem description

Historically in OpenStack, we haven’t had a way of automatically verifying that the detach process doesn’t leave behind orphaned volumes. I define orphaned volumes as volume paths on a system that were associated with a volume, that has been detached.

This can cause problems later on when volumes are attached to that host. Some SAN arrays reuse iqn’s and or LUN ids for volumes. This can get a host in the state where a volume on the host conflicts with an orphaned volume path on the host, leading to corruption with i/o.

Use Cases

The primary use case is for fetching the list of existing paths for a volume on a system after attach and detach.

Proposed change

Add new APIs to each os-brick connector to 1) fetch the existing paths on the system for a given volume. 2) fetch all of the volume paths for a connector.

Flask based API script. Add a new flask script that exposes these API calls that can be run in a test environment. This flask script is needed in order to automatically verify the success of detach during nova live migration which happens on multiple compute hosts. This flask script is only intended on being used during jenkins tests and gate checking.

Alternatives

Someone can write individual verification scripts, outside of os-brick, for each type of volume (connector), but won’t benefit from future fixes in connectors.

Data model impact

None

REST API impact

None

Security impact

os-brick already returns a single path entry after connect_volume calls. What os-brick doesn’t do today is return a list of all volume paths associated with a connector.

It’s noted here that the flask script as described in the proposed change, should not be run/used on a production/live system. This is intended for check/gate testing only.

Notifications impact

None

Other end user impact

None

Performance Impact

None

Other deployer impact

None

Developer impact

Connector developers will be required to implement the new APIs for their connector, even if they are stubs.

Implementation

Assignee(s)

Primary assignee:
walter-boring
Other contributors:
anthony-mic-lee

Work Items

I have a Work In Progress patch already up in gerrit for the API work. We need to add a follow up patch that creates the flask script for remotely calling the methods for the connector.

Dependencies

None

Testing

Standard unit tests. I have also done manual testing with it. Eventually, we would like to add verification in check/gate testing for volume attaches as well. For each connector object we should have 3rd party CI to test the new APIs as well.

Documentation Impact

The code is documented.

References

The existing patch in gerrit * https://review.openstack.org/#/c/199764/

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