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[Balazs Gibizer <1917645@xxxxxxxxxxxxxxxxxx>]

I'm setting the nova part of this bug as Invalid as the this is fixed by
an oslo.messaging patch.

** Changed in: nova
       Status: Confirmed => Invalid

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https://bugs.launchpad.net/bugs/1917645

Title:
  Nova can't create instances if RabbitMQ notification cluster is down

Status in OpenStack Compute (nova):
  Invalid
Status in oslo.messaging:
  Fix Released

Bug description:
  We use independent RabbitMQ clusters for each OpenStack project, Nova
  Cells and also for notifications. Recently, I noticed in our test
  infrastructure that if the RabbitMQ cluster for notifications has an
  outage, Nova can't create new instances. Possibly other operations
  will also hang.

  Not being able to send a notification/connect to the RabbitMQ cluster
  shouldn't stop new instances to be created. (If this is actually an
  use-case for some deployments, the operator should have the
  possibility to configure it.)

  Tested against the master branch.

  If the notification RabbitMQ is stooped, when creating an instance,
  nova-scheduler is stuck with:

  ```
  Mar 01 21:16:28 devstack nova-scheduler[18384]: DEBUG nova.scheduler.request_filter [None req-353318d1-f4bd-499d-98db-a0919d28ecf7 demo demo] Request filter 'accelerators_filter' took 0.0 seconds {{(pid=18384) wrapper /opt/stack/nova/nova/scheduler/request_filter.py:46}}
  Mar 01 21:16:32 devstack nova-scheduler[18384]: ERROR oslo.messaging._drivers.impl_rabbit [None req-353318d1-f4bd-499d-98db-a0919d28ecf7 demo demo] Connection failed: [Errno 113] EHOSTUNREACH (retrying in 2.0 seconds): OSError: [Errno 113] EHOSTUNREACH
  Mar 01 21:16:35 devstack nova-scheduler[18384]: ERROR oslo.messaging._drivers.impl_rabbit [None req-353318d1-f4bd-499d-98db-a0919d28ecf7 demo demo] Connection failed: [Errno 113] EHOSTUNREACH (retrying in 4.0 seconds): OSError: [Errno 113] EHOSTUNREACH
  Mar 01 21:16:42 devstack nova-scheduler[18384]: ERROR oslo.messaging._drivers.impl_rabbit [None req-353318d1-f4bd-499d-98db-a0919d28ecf7 demo demo] Connection failed: [Errno 113] EHOSTUNREACH (retrying in 6.0 seconds): OSError: [Errno 113] EHOSTUNREACH
  Mar 01 21:16:51 devstack nova-scheduler[18384]: ERROR oslo.messaging._drivers.impl_rabbit [None req-353318d1-f4bd-499d-98db-a0919d28ecf7 demo demo] Connection failed: [Errno 113] EHOSTUNREACH (retrying in 8.0 seconds): OSError: [Errno 113] EHOSTUNREACH
  Mar 01 21:17:02 devstack nova-scheduler[18384]: ERROR oslo.messaging._drivers.impl_rabbit [None req-353318d1-f4bd-499d-98db-a0919d28ecf7 demo demo] Connection failed: [Errno 113] EHOSTUNREACH (retrying in 10.0 seconds): OSError: [Errno 113] EHOSTUNREACH
  (...)
  ```

  Because the notification RabbitMQ cluster is down, Nova gets stuck in:

  https://github.com/openstack/nova/blob/5b66caab870558b8a7f7b662c01587b959ad3d41/nova/scheduler/filter_scheduler.py#L85

  because oslo messaging never gives up:

  https://github.com/openstack/oslo.messaging/blob/5aa645b38b4c1cf08b00e687eb6c7c4b8a0211fc/oslo_messaging/_drivers/impl_rabbit.py#L736

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