[Bug 1452641] Re: Static Ceph mon IP addresses in connection_info can prevent VM startup

[melanie witt]

FWIW, as of the Xena release [1], there are nova-manage commands
available for the purpose of pulling fresh volume connection_info from
Cinder API and updating instance block device mapping records in the
database without disrupting the instance:

https://docs.openstack.org/nova/latest/cli/nova-manage.html#volume-
attachment-refresh


As for automatically refreshing connection_info, at the Queens PTG we had consensus to add refresh of connection_info to various server action paths that generate new libvirt XML [2] but we did not have anyone available to do the work at the time.

Some had concerns about the overhead of always querying Cinder API for
new connection_info on particular server actions when the changing of
connection_info is a relatively rare event, which likely informed the
work on the 'nova-manage volume_attachment' commands.

If the nova-manage commands are not sufficient for operator use cases,
we would like to know that along with how high of priority it is from
operators' perspectives.

[1] https://docs.openstack.org/releasenotes/nova/xena.html#relnotes-24-0-0-stable-xena-new-features
[2] https://lists.openstack.org/pipermail/openstack-dev/2017-September/122170.html

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https://bugs.launchpad.net/bugs/1452641

Title:
  Static Ceph mon IP addresses in connection_info can prevent VM startup

Status in OpenStack Compute (nova):
  Confirmed
Status in nova package in Ubuntu:
  Triaged

Bug description:
  The Cinder rbd driver extracts the IP addresses of the Ceph mon servers from the Ceph mon map when the instance/volume connection is established. This info is then stored in nova's block-device-mapping table and is never re-validated down the line. 
  Changing the Ceph mon servers' IP adresses will prevent the instance from booting as the stale connection info will enter the instance's XML. One idea to fix this would be to use the information from ceph.conf, which should be an alias or a loadblancer, directly.

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