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Add another up-call to the cells v2 caveats list

Due to change I8d426f2635232ffc4b510548a905794ca88d7f99 in Pike,
which ironically was meant to avoid up-calls (I think), it
introduced an up-call during reschedules for server create and
resize to set the instance.availability_zone based on the
alternate host selected during the reschedule.

This adds the up-call to our list of known issues in the cells
v2 docs so we can track the issue and make people aware of it.

Change-Id: Id819f91477613a013b89b1fb0b2def3b0fd4b08c
Related-Bug: #1781286
tags/18.0.0.0rc1
Matt Riedemann 1 year ago
parent
commit
1160ae7a65
1 changed files with 10 additions and 1 deletions
  1. 10
    1
      doc/source/user/cellsv2-layout.rst

+ 10
- 1
doc/source/user/cellsv2-layout.rst View File

@@ -320,7 +320,7 @@ implement some features without such connectivity. Thus, anything that
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 requires a so-called "upcall" will not function. This impacts the
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 following:
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-#. Instance reschedules during boot and resize
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+#. Instance reschedules during boot and resize (part 1)
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    .. note:: This has been resolved in the Queens release [#]_.
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@@ -331,6 +331,7 @@ following:
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    .. note:: This has been resolved in the Rocky release [#]_.
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 #. Attaching a volume and ``[cinder]/cross_az_attach=False``
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+#. Instance reschedules during boot and resize (part 2)
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 The first is simple: if you boot an instance, it gets scheduled to a
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 compute node, fails, it would normally be re-scheduled to another
@@ -369,6 +370,14 @@ volume and must tell Cinder in which availability zone to create the volume.
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 Long-term, volume creation during boot from volume should be moved to the
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 top-level superconductor which would eliminate this AZ up-call check problem.
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+The sixth is detailed in `bug 1781286`_ and similar to the first issue.
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+The issue is that servers created without a specific availability zone
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+will have their AZ calculated during a reschedule based on the alternate host
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+selected. Determining the AZ for the alternate host requires an "up call" to
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+the API DB.
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+
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+.. _bug 1781286: https://bugs.launchpad.net/nova/+bug/1781286
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+
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 .. [#] https://blueprints.launchpad.net/nova/+spec/efficient-multi-cell-instance-list-and-sort
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 .. [#] https://specs.openstack.org/openstack/nova-specs/specs/queens/approved/return-alternate-hosts.html
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 .. [#] https://blueprints.launchpad.net/nova/+spec/live-migration-in-xapi-pool

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