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[OpenStack Infra <1917645@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.opendev.org/c/openstack/oslo.messaging/+/819142
Committed: https://opendev.org/openstack/oslo.messaging/commit/7b3968d9b012e873a9b393fcefa578c46fca18c6
Submitter: "Zuul (22348)"
Branch:    master

commit 7b3968d9b012e873a9b393fcefa578c46fca18c6
Author: Balazs Gibizer <balazs.gibizer@xxxxxxxx>
Date:   Tue Nov 23 16:58:05 2021 +0100

    [rabbit] use retry parameters during notification sending
    
    The rabbit backend now applies the [oslo_messaging_notifications]retry,
    [oslo_messaging_rabbit]rabbit_retry_interval, rabbit_retry_backoff and
    rabbit_interval_max configuration parameters when tries to establish the
    connection to the message bus during notification sending.
    
    This patch also clarifies the differences between the behavior
    of the kafka and the rabbit drivers in this regard.
    
    Closes-Bug: #1917645
    Change-Id: Id4ccafc95314c86ae918336e42cca64a6acd4d94


** Changed in: oslo.messaging
       Status: In Progress => Fix Released

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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):
  Confirmed
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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