[Bug 1789177] Re: RabbitMQ fails to synchronize exchanges under high load

[Seyeong Kim]

I confirmed that upgrading olso.messaging in n-ovs causes rabbitmq issue

Right after restarted n-ovs-agent, I can see a lot of errors in rabbitmq log[1]
which is the same as the error when rabbitmq failover issue ( the original issue of this LP )

Then after I upgraded oslo.messaging  in neutron-api unit  and restarted
neutron-server, below errors are gone and I was able to create instance
again.

After upgrading oslo.messaging in n-ovs only, exchange they communicate didn't match.
As changing exchanges they use  depends on publisher-cosumer relation.

So I think there are two ways.
1. revert this patch for Q ( original failover problem will be there )
2. upgrade them with maintenance window

Thanks a lot

[1]
################################################################################
=ERROR REPORT==== 3-Feb-2021::03:25:26 ===
Channel error on connection <0.2379.1> (10.0.0.32:60430 -> 10.0.0.34:5672, vhost: 'openstack', user: 'neutron'), channel 1:
{amqp_error,not_found,
            "no exchange 'reply_7da3cecc31b34bdeb96c866dc84e3044' in vhost 'openstack'",
            'basic.publish'}

10.0.0.32 is neutron-api unit

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https://bugs.launchpad.net/bugs/1789177

Title:
  RabbitMQ fails to synchronize exchanges under high load

Status in Ubuntu Cloud Archive:
  New
Status in Ubuntu Cloud Archive mitaka series:
  New
Status in Ubuntu Cloud Archive queens series:
  Fix Committed
Status in Ubuntu Cloud Archive rocky series:
  New
Status in Ubuntu Cloud Archive stein series:
  Fix Released
Status in Ubuntu Cloud Archive train series:
  Fix Released
Status in oslo.messaging:
  Fix Released
Status in python-oslo.messaging package in Ubuntu:
  Fix Released
Status in python-oslo.messaging source package in Xenial:
  In Progress
Status in python-oslo.messaging source package in Bionic:
  Fix Released

Bug description:
  [Impact]

  If there are many exchanges and queues, after failing over, rabbitmq-
  server shows us error that exchanges are cannot be found.

  Affected
   Bionic (Queens)
  Not affected
   Focal

  [Test Case]

  1. deploy simple rabbitmq cluster
  - https://pastebin.ubuntu.com/p/MR76VbMwY5/
  2. juju ssh neutron-gateway/0
  - for i in {1..1000}; do systemd restart neutron-metering-agent; sleep 2; done
  3. it would be better if we can add more exchanges, queues, bindings
  - rabbitmq-plugins enable rabbitmq_management
  - rabbitmqctl add_user test password
  - rabbitmqctl set_user_tags test administrator
  - rabbitmqctl set_permissions -p openstack test ".*" ".*" ".*"
  - https://pastebin.ubuntu.com/p/brw7rSXD7q/ ( save this as create.sh) [1]
  - for i in {1..2000}; do ./create.sh test_$i; done

  4. restart rabbitmq-server service or shutdown machine and turn on several times.
  5. you can see the exchange not found error

  
  [1] create.sh (pasting here because pastebins don't last forever)
  #!/bin/bash

  rabbitmqadmin declare exchange -V openstack name=$1 type=direct -u test -p password
  rabbitmqadmin declare queue -V openstack name=$1 durable=false -u test -p password 'arguments={"x-expires":1800000}'
  rabbitmqadmin -V openstack declare binding source=$1 destination_type="queue" destination=$1 routing_key="" -u test -p password


  [Where problems could occur]
  1. every service which uses oslo.messaging need to be restarted.
  2. Message transferring could be an issue

  [Others]

  // original description

  Input:
   - OpenStack Pike cluster with ~500 nodes
   - DVR enabled in neutron
   - Lots of messages

  Scenario: failover of one rabbit node in a cluster

  Issue: after failed rabbit node gets back online some rpc communications appear broken
  Logs from rabbit:

  =ERROR REPORT==== 10-Aug-2018::17:24:37 ===
  Channel error on connection <0.14839.1> (10.200.0.24:55834 -> 10.200.0.31:5672, vhost: '/openstack', user: 'openstack'), channel 1:
  operation basic.publish caused a channel exception not_found: no exchange 'reply_5675d7991b4a4fb7af5d239f4decb19f' in vhost '/openstack'

  Investigation:
  After rabbit node gets back online it gets many new connections immediately and fails to synchronize exchanges for some reason (number of exchanges in that cluster was ~1600), on that node it stays low and not increasing.

  Workaround: let the recovered node synchronize all exchanges - forbid
  new connections with iptables rules for some time after failed node
  gets online (30 sec)

  Proposal: do not create new exchanges (use default) for all direct
  messages - this also fixes the issue.

  Is there a good reason for creating new exchanges for direct messages?

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