From 916ba166c8ecb726d9ced26d7bbce3e25c6bbeff Mon Sep 17 00:00:00 2001 From: Dan Smith Date: Thu, 3 Aug 2017 10:49:43 -0700 Subject: [PATCH] Add a caveat section about cellsv2 upcalls This adds another subsection to the caveat section about operations that require upcalls in Pike not being supported. Change-Id: If95be4f631f929cd8c6528671433ae0fc747a6be --- doc/source/user/cellsv2_layout.rst | 32 ++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/doc/source/user/cellsv2_layout.rst b/doc/source/user/cellsv2_layout.rst index 137fa5733dc4..9ce950077a0d 100644 --- a/doc/source/user/cellsv2_layout.rst +++ b/doc/source/user/cellsv2_layout.rst @@ -291,3 +291,35 @@ Neutron Metadata API proxy The Neutron metadata API proxy should be global across all cells, and thus be configured as an API-level service with access to the ``[api_database]/connection`` information. + +Operations Requiring upcalls +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +If you deploy multiple cells with a superconductor as described above, +computes and cell-based conductors will not have the ability to speak +to the scheduler as they are not connected to the same MQ. This is by +design for isolation, but currently the processes are not in place to +implement some features without such connectivity. Thus, anything that +requires a so-called "upcall" will not function. This impacts the +following: + +- Instance reschedules during boot +- Instance affinity reporting from the compute nodes to scheduler +- The late anti-affinity check + +The first is simple: if you boot an instance, it gets scheduled to a +compute node, fails, it would normally be re-scheduled to another +node. That requires scheduler intervention and thus it will not work +in Pike with a multi-cell layout. If you do not rely on reschedules +for covering up transient compute-node failures, then this will not +affect you. To ensure you do not make futile attempts at rescheduling, +you should set ``[scheduler]/max_attempts=1`` in ``nova.conf``. + +The second two are related. The summary is that some of the facilities +that Nova has for ensuring that affinty/anti-affinity is preserved +between instances does not function in Pike with a multi-cell +layout. If you don't use affinity operations, then this will not +affect you. To make sure you don't make futile attempts at the +affinity check, you should set +``[workarounds]/disable_group_policy_check_upcall=True`` and +``[filter_scheduler]/track_instance_changes=False`` in ``nova.conf``.