cinder-specs/specs/queens/report-backend-state-in-service-list.rst

Report backend state in service list

https://blueprints.launchpad.net/cinder/+spec/report-backend-state-in-service-list

Storage driver reports state of backend storage device and let admin operator know it via service list for maintenance purpose.

Problem description

Currently, Cinder couldn't report backend state to service, operators only know that cinder-volume process is up, but isn't aware of whether the backend storage device is ok. Users still can create volume and go to fail over and over again. To make maintenance easier, operator could query storage device state via service list and fix the problem more quickly. If device state is down, that means volume creation will fail.

Use Cases

In large scale cloud system, there could be many backends existing in the system. If volume, snapshot or other resources creation goes to failure, operators or cloud management system could query the service first and get the backend device state in every service. If device state is down, specify that storage device has got some problems. Give operators/management system more information to locate bug more quickly.

Proposed change

• Each driver reports the backend state in "get_volume_stats" by adding key/value: "backend_state: up/down"[1].
• When calling 'service list', get this information from scheduler for every backend.
• Add 'backend_state: up/down' in response body of service list API if context is admin.
• Before all drivers support this feature, if the result of get_volume_stats doesn't include the backend state, Cinder will set backend_state to 'up' by default.

Alternatives

Add cinder manage command to query backend device state from driver directly.

Data model impact

None

REST API impact

Add backend_state: up/down into response body of service list and also need a microversions for this feature:

GET /v3/{project_id}/os-services

RESP BODY:

{"services": [{"host": "host@backend1",
               ...,
               "backend_status": "up",
              },
              {"host": "host@backend2",
               ...,
               "backend_status": "down",
              }]
}

Security impact

None

Notifications impact

None.

Other end user impact

None

Performance Impact

None

Other deployer impact

None

Developer impact

Driver maintainer needs to add backend state when reporting volume stats.

Implementation

Assignee(s)

Primary assignee:

wanghao<wanghao749@huawei.com>

Work Items

• Implement code in Cinder API and scheduler.
• Update cinderclient to support this function.
• Add change to API doc.

Dependencies

None

Testing

Both unit and Tempest tests need to be created to cover the code change that mentioned in "Proposed change".

Documentation Impact

1. The cinder API documentation will need to be updated to reflect the REST API changes.

References

[1]https://docs.openstack.org/cinder/latest/contributor/drivers.html