nova/releasenotes/notes/records-list-skip-down-cells-84d995e75c77c041.yaml
Surya Seetharaman 21c5f3e2e5 Making instance/migration listing skipping down cells configurable
Presently if a cell is down, the instances in that cell are
skipped from results. Sometimes this may not be desirable for
operators as it may confuse the users who saw more instances in
their previous listing than now. This patch adds a new api config
option called list_records_by_skipping_down_cells which can be set to
False (True by default) if the operator desires to just return an
API error altogether if the user has any instance in the down cell
instead of skipping. This is essentially a configurable revert of
change I308b494ab07f6936bef94f4c9da45e9473e3534d for bug 1726301 so
that operators can opt into the 500 response behaviour during listing.

Change-Id: Id749761c58d4e1bc001b745d49b6ff0f3732e133
Related-Bug: #1726301
2018-09-20 22:02:26 +02:00

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In case of infrastructure failures like non-responsive cells, prior to
`change e3534d`_ we raised an API 500 error. However currently when
listing instances or migrations, we skip that cell and display results from
the up cells with the aim of increasing availability at the expense of
accuracy. If the old behaviour is desired, a new flag called
``CONF.api.list_records_by_skipping_down_cells`` has been added which can
be set to False to mimic the old behavior. Both of these potential
behaviors will be unified in an upcoming microversion done through the
`blueprint handling-down-cell`_ where minimal constructs would be returned
for the down cell instances instead of raising 500s or skipping down cells.
.. _change e3534d : https://review.openstack.org/#/q/I308b494ab07f6936bef94f4c9da45e9473e3534d
.. _blueprint handling-down-cell: https://blueprints.launchpad.net/nova/+spec/handling-down-cell