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Merge "Guide to review neutron routers in OVS/ML2"

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doc/source/admin/index.rst
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@ -15,6 +15,7 @@ General cloud operations:
ops-unseal-vault
ops-config-tls-vault-api
ops-live-migrate-vms
ops-live-migrate-routers
ops-replace-vault-node
ops-scale-out-nova-compute
ops-start-innodb-from-outage

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doc/source/admin/ops-live-migrate-routers.rst Normal file
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======================================
Live migrate Neutron routers (OVS/ML2)
======================================
Introduction
------------
Neutron routers are hosted by ``L3 Agents`` running on `neutron-gateway`_
units. When the unit(s) need to be brought down for maintenance, routers need
to be migrated to another unit that will host them during the downtime.
.. note::
This tutorial deals with migration of a router strictly in the OVS/ML2
environment, deployments using OVN have different topology in which routers
are not hosted by individual ``L3 Agents``.
.. warning::
Migration of a router will cause brief disruption of a traffic between
networks connected to the router.
Example topology
----------------
To demonstrate steps needed for the migration, we will use openstack deployment
with three `neutron-gateway`_ units:
.. code-block:: console
Unit Workload Agent Machine Public address Ports Message
neutron-gateway/0* active idle 0 10.5.1.149 Unit is ready
ntp/0* active idle 10.5.1.149 123/udp chrony: Ready
neutron-gateway/1 active idle 13 10.5.2.17 Unit is ready
ntp/4 active idle 10.5.2.17 123/udp chrony: Ready
neutron-gateway/2 active idle 14 10.5.0.159 Unit is ready
ntp/5 active idle 10.5.0.159 123/udp chrony: Ready
Machine State DNS Inst id Series AZ Message
0 started 10.5.1.149 1bf707d8-3e27-473f-b597-5cfc43c50b85 bionic nova ACTIVE
13 started 10.5.2.17 960d3868-a5a3-443c-99a8-acbcec7a4272 bionic nova ACTIVE
14 started 10.5.0.159 c8c75144-7a5b-49c0-bfb5-4910c6501f21 bionic nova ACTIVE
Each of these units hosts single ``L3 Agent``:
.. code-block:: console
openstack network agent list --agent-type l3
+--------------------------------------+------------+-------------------+-------------------+-------+-------+------------------+
| ID | Agent Type | Host | Availability Zone | Alive | State | Binary |
+--------------------------------------+------------+-------------------+-------------------+-------+-------+------------------+
| 6226d159-ed57-4dfb-a311-ae36d2b4462b | L3 agent | juju-56ea63-os-0 | nova | :-) | UP | neutron-l3-agent |
| 6ae7ed32-7aa4-460c-8eb7-d13f4e651fcc | L3 agent | juju-56ea63-os-13 | nova | :-) | UP | neutron-l3-agent |
| b066c34d-aa91-46fe-9b20-f19f4a297932 | L3 agent | juju-56ea63-os-14 | nova | :-) | UP | neutron-l3-agent |
+--------------------------------------+------------+-------------------+-------------------+-------+-------+------------------+
And we will be bringing down unit ``neutron-gateway/2`` for maintenance.
Procedure
---------
Find out which routers run on our targeted unit
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Referencing our example topology above, we are about to bring down unit
``neutron-gateway/2``. We need to find out which routers are hosted on it.
We can see that this unit is running on machine ``14``, listing all the
L3 Agents we get:
.. code-block:: console
openstack network agent list --agent-type l3
+--------------------------------------+------------+-------------------+-------------------+-------+-------+------------------+
| ID | Agent Type | Host | Availability Zone | Alive | State | Binary |
+--------------------------------------+------------+-------------------+-------------------+-------+-------+------------------+
| 6226d159-ed57-4dfb-a311-ae36d2b4462b | L3 agent | juju-56ea63-os-0 | nova | :-) | UP | neutron-l3-agent |
| 6ae7ed32-7aa4-460c-8eb7-d13f4e651fcc | L3 agent | juju-56ea63-os-13 | nova | :-) | UP | neutron-l3-agent |
| b066c34d-aa91-46fe-9b20-f19f4a297932 | L3 agent | juju-56ea63-os-14 | nova | :-) | UP | neutron-l3-agent |
+--------------------------------------+------------+-------------------+-------------------+-------+-------+------------------+
Machine ``14`` corresponds to Host ``juju-56ea63-os-14``, so we need to find
out which routers are hosted on the ``L3 agent`` with ID
``b066c34d-aa91-46fe-9b20-f19f4a297932``.
.. code-block:: console
openstack router list --agent b066c34d-aa91-46fe-9b20-f19f4a297932
+--------------------------------------+-----------------+--------+-------+-------------+-------+----------------------------------+
| ID | Name | Status | State | Distributed | HA | Project |
+--------------------------------------+-----------------+--------+-------+-------------+-------+----------------------------------+
| 35dcce1b-f69f-4af3-b46f-54249812ec9f | provider-router | ACTIVE | UP | False | False | b800e60c5e3841fbbb8b1dbc02ce13e3 |
+--------------------------------------+-----------------+--------+-------+-------------+-------+----------------------------------+
This means that we need to move router with name ``provider-router`` to a
different agent.
Move router to a different agent
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This is the part that will cause brief disruption of a traffic as routers can
not be moved seamlessly. Moving consists of manually removing router from one
agent and adding it to another. First we double-check that the router is hosted
on the agent that is about to go down:
.. code-block:: console
openstack network agent list --router provider-router
+--------------------------------------+------------+-------------------+-------------------+-------+-------+------------------+
| ID | Agent Type | Host | Availability Zone | Alive | State | Binary |
+--------------------------------------+------------+-------------------+-------------------+-------+-------+------------------+
| b066c34d-aa91-46fe-9b20-f19f4a297932 | L3 agent | juju-56ea63-os-14 | nova | :-) | UP | neutron-l3-agent |
+--------------------------------------+------------+-------------------+-------------------+-------+-------+------------------+
Now we remove the router from this agent and assign it to an agent running on
the unit ``neutron-gateway/0`` with agent ID
``6226d159-ed57-4dfb-a311-ae36d2b4462b``. Note that this will increase the load
on the ``neutron-gateway/0`` unit. Make sure that the machine hosting this unit
has enough resources to accommodate the additional router.
.. code-block:: console
openstack network agent remove router b066c34d-aa91-46fe-9b20-f19f4a297932 provider-router --l3
openstack network agent add router 6226d159-ed57-4dfb-a311-ae36d2b4462b provider-router --l3
Result of this move can be checked by:
.. code-block:: console
openstack network agent list --router provider-router
+--------------------------------------+------------+------------------+-------------------+-------+-------+------------------+
| ID | Agent Type | Host | Availability Zone | Alive | State | Binary |
+--------------------------------------+------------+------------------+-------------------+-------+-------+------------------+
| 6226d159-ed57-4dfb-a311-ae36d2b4462b | L3 agent | juju-56ea63-os-0 | nova | :-) | UP | neutron-l3-agent |
+--------------------------------------+------------+------------------+-------------------+-------+-------+------------------+
.. LINKS
.. _neutron-gateway : https://charmhub.io/neutron-gateway