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:
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:
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:
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.
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:
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.
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:
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 |
+--------------------------------------+------------+------------------+-------------------+-------+-------+------------------+
