Chapter 2. Migrating the ML2 mechanism driver from OVS to OVN

Procedure

1. Create an ML2/OVN stage deployment to obtain the baseline configuration of your target ML2/OVN deployment and test the feasibility of the target deployment.

   Design the stage deployment with the same basic roles, routing, and topology as the planned post-migration production deployment. Save the full openstack overcloud deploy command, along with all deployment arguments, into a file called overcloud-deploy.sh. Also save any files referenced by the openstack overcloud deploy command, such as environment files. You need these files later in this procedure to configure the migration’s target ML2/OVN environment.

   Note

   Use these files only for creation of the stage deployment and in the migration. Do not re-use them after the migration.

2. Install openstack-neutron-ovn-migration-tool.

   sudo dnf install openstack-neutron-ovn-migration-tool

3. Copy the overcloud-deploy.sh script that you created in Step 1 and rename the copy to overcloud-migrate-ovn.sh. Confirm that all paths for the overcloud deploy command inside the overcloud-migrate-ovn.sh are still correct. You customize some arguments in the overcloud-migrate-ovn.sh script in subsequent steps.

4. Find your migration scenario in the following list and perform the appropriate steps to customize the openstack deploy command in overcloud-migrate-ovn.sh.

   In the deployment command, pay careful attention to the order of the -e arguments that add environment files. The environment file with the generic defaults (such as neutron-ovn-dvr-ha.yaml) must precede the -e argument that specifies the file with custom network environment settings such as bridge mappings.

   Scenario 1: DVR to DVR, Compute nodes have connectivity to the external network

   • In overcloud-migrate-ovn.sh, add custom heat template file arguments to the openstack overcloud deploy command. Add them after the core template file arguments.

     The following command example uses the default neutron-ovn-dvr-ha.yaml heat template file. Your deployment might use multiple heat files to define your OVN environment. Add each with a separate -e argument.

     openstack overcloud deploy \
     --templates /usr/share/openstack-tripleo-heat-templates \
     ...
     -e /usr/share/openstack-tripleo-heat-templates/environments/services/ \
     neutron-ovn-dvr-ha.yaml

   Scenario 2: Centralized routing to centralized routing (no DVR)

   • If your deployment uses SR-IOV and other NFV features, in overcloud-migrate-ovn.sh, use -e arguments to add the SR-IOV environment parameters to the openstack overcloud deploy command. Add the SR-IOV environment files after the core template environment file arguments and other custom environment file arguments. For an example of SR-IOV environment file, see /usr/share/openstack-tripleo-heat-templates/environments/services/neutron-ovn-sriov.yaml.
   • Leave any custom network modifications the same as they were before migration.

   Scenario 3: Centralized routing to DVR, and Compute nodes connected to external networks through br-ex

   • Ensure that Compute nodes are connected to the external network through the br-ex bridge. For example, in an environment file such as compute-dvr.yaml, set the following parameters. Then use -e to add the environment file to the openstack overcloud deploy command in the script overcloud-migrate-ovn.sh:

     type: ovs_bridge
         # Defaults to br-ex, anything else requires specific # bridge mapping entries for it to be used.
         name: bridge_name
         use_dhcp: false
         members:
          -
           type: interface
           name: nic3
           # force the MAC address of the bridge to this interface
           primary: true

5. Add the following arguments at the end of the overcloud deploy command in overcloud-migrate-ovn.sh:

   -e /usr/share/openstack-tripleo-heat-templates/environments/disable-container-manage-clean-orphans.yaml \
   -e $HOME/ovn-extras.yaml

6. If router appears as a value for NeutronServicePlugins or NeutronPluginExtensions in any environment file or template, replace the value router with ovn-router. For example, in tripleo-heat-templates/environments/services/neutron-ovn-dvr-ha.yaml:

   parameter_defaults:
      NeutronServicePlugins: "ovn-router,trunk,qos,placement"

7. Ensure that all users have execution privileges on the file overcloud-migrate-ovn.sh. The script requires execution privileges during the migration process.

   $ chmod a+x ~/overcloud-migrate-ovn.sh

8. Use export commands to set the following migration-related environment variables. For example:

   $ export OVERCLOUDRC_FILE=~/myovercloudrc

   STACKRC_FILE

   The stackrc file in your undercloud.

   Default: ~/stackrc

   OVERCLOUDRC_FILE

   The overcloudrc file in your undercloud.

   Default: ~/overcloudrc

   OVERCLOUD_OVN_DEPLOY_SCRIPT

   The deployment script.

   Default: ~/overcloud-migrate-ovn.sh

   DHCP_RENEWAL_TIME

   DHCP renewal time in seconds to configure in DHCP agent configuration file.

   Default: 30

9. Ensure that you are in the ovn-migration directory and run the command ovn_migration.sh generate-inventory to generate the hosts_for_migration inventory file and the ansible.cfg file:

   $ ovn_migration.sh generate-inventory   | sudo tee -a /var/log/ovn_migration_output.txt

10. Review the hosts_for_migration file for accuracy:

    • Ensure the lists match your environment.
    • Ensure there are ovn controllers on each node.
    • Ensure there are no list headings (such as [ovn-controllers]) that do not have list items under them.
    • From the ovn-migration` directory, run the command ansible -i hosts_for_migration -m ping all

11. (Optional) Back up the deployment to prepare a potential migration revert in the case that something unexpected happens during migration.

    1. Use export commands to set the following environment variables if you plan to use the `ovn-migration.sh backup`command to back up the controller nodes:

       BACKUP_MIGRATION_IP

       The IP address of the server where backup is stored.

       Default: 192.168.24.1

       BACKUP_MIGRATION_CTL_PLANE_CIDRS

       A comma-separated string of control plane subnets in CIDR notation for all nodes that will be backed up.

       Default: 192.168.24.0/24

       You can see a list of all relevant environment variables in the beginning of /usr/bin/ovn_migraton.sh file.

       CONTROLLER_GROUP

       Host group name used by Ansible to back up controllers.

       Default: Controller

       If your controller group has a name other than Controller, export that name as the value of CONTROLLER_GROUP. For example, in SR-IOV environments, the controller group name might be ControllerSriov.

       OVERCLOUD_OVS_REVERT_SCRIPT

       Used to optionally revert from an unsuccessful OVN migration if you created the optional backup.

       Default: ~/overcloud-revert-ovs.sh

    2. Back up the control plane. Use the backup mechanism of your choice to back up the controller nodes. The supported choice is the default ovn-migration.sh backup command, which uses the ReaR backup tool.

       $ ovn_migration.sh backup

    3. Back up the templates and environment files that were used to deploy the overcloud. The ovn-migration.sh backup command does not back up the overcloud. If you need to revert the controller nodes after a partial or failed migration, then you will need this backup to restore the OVS overcloud.

    4. Copy the script that you used to deploy the original RHOSP 17.1 ML2/OVS deployment. For example, the original script might be named overcloud_deploy.sh. Name the copy overcloud-revert-ovs.sh.

       Warning

       If overcloud-revert-ovs.sh creates a file, make sure to specify an absolute path to that file. For example, if you use the --log-file argument, specify the file with an absolute path. The migration revert playbook uses the variable $ANSIBLE_DIR (which defaults to /usr/share/ansible/neutron-ovn-migration). If your creates a file on a relative path, Ansible tries to write it in $ANSIBLE_DIR, where the revert user might not have adequate permissions.

    5. Create a file /home/stack/ovs-extra.yml with the following contents:

       parameter_defaults:
         ForceNeutronDriverUpdate: true

    6. Ensure that the final environment file argument in overcloud-revert-ovs.sh is the following.

       -e /home/stack/ovs-extra.yml

    7. Store overcloud-revert-ovs.sh securely. You will need it if you revert a failed migration. .
12. Proceed to Section 2.2, “Preparing container images for migration of the ML2 mechanism driver from OVS to OVN”.

Procedure

1. Prepare the new container images for use after the migration to ML2/OVN.

   1. Create containers-prepare-parameter.yaml file in the home directory if it is not present.

      $ test -f $HOME/containers-prepare-parameter.yaml || sudo openstack tripleo container image prepare default \
      --output-env-file $HOME/containers-prepare-parameter.yaml

   2. Verify that containers-prepare-parameter.yaml is present at the end of your $HOME/overcloud-migrate-ovn.sh and $HOME/overcloud-deploy.sh files.

   3. Change the neutron_driver in the containers-prepare-parameter.yaml file to ovn:

      $ sed -i -E 's/neutron_driver:([ ]\w+)/neutron_driver: ovn/' $HOME/containers-prepare-parameter.yaml

   4. Verify the changes to the neutron_driver:

      $ grep neutron_driver $HOME/containers-prepare-parameter.yaml
      neutron_driver: ovn

   5. Update the images:

      $ sudo openstack tripleo container image prepare \
      --environment-file /home/stack/containers-prepare-parameter.yaml

      Note

      Provide the full path to your containers-prepare-parameter.yaml file. Otherwise, the command completes very quickly without updating the image list or providing an error message.

2. On the undercloud, validate the updated images.

   . Log in to the undercloud as the user `stack` and source the stackrc file.
   $ source ~/stackrc
   $ openstack tripleo container image list | grep  '\-ovn'

   Your list should resemble the following example. It includes containers for the OVN databases, OVN controller, the metadata agent, and the neutron server agent.

   docker://undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp17-openstack-ovn-northd:17.1_20240725.1
   docker://undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp17-openstack-ovn-sb-db-server:17.1_20240725.1
   docker://undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp17-openstack-ovn-controller:17.1_20240725.1
   docker://undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp17-openstack-neutron-server-ovn:17.1_20240725.1
   docker://undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp17-openstack-ovn-nb-db-server:17.1_20240725.1
   docker://undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp17-openstack-neutron-metadata-agent-ovn:17.1_20240725.1

   If you are migrating to the OVN mechanism driver in RHOSP 16.2, the listings resemble the following:

   docker://undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp16-openstack-ovn-northd:16.2_20211110.2
   docker://undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp16-openstack-ovn-sb-db-server:16.2_20211110.2
   docker://undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp16-openstack-ovn-controller:16.2_20211110.2
   docker://undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp16-openstack-neutron-server-ovn:16.2_20211110.2
   docker://undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp16-openstack-ovn-nb-db-server:16.2_20211110.2
   docker://undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp16-openstack-neutron-metadata-agent-ovn:16.2_20211110.2

3. If your original deployment uses VXLAN, you might need to adjust maximum transmission unit (MTU) values. Proceed to Section 2.3, “Lowering MTU for migration from a VXLAN OVS deployment”.

   If your original deployment uses VLAN networks, you can skip the MTU adjustments and proceed to Section 2.4, “Migrating the ML2 mechanism driver from OVS to OVN”.

Procedure

1. Run ovn_migration.sh `reduce-dhcp-t1. This lowers the T1 parameter of the internal neutron DHCP servers that configure the dhcp_renewal_time in /var/lib/config-data/puppet-generated/neutron/etc/neutron/dhcp_agent.ini in all the nodes where DHCP agent is running.

   $ ovn_migration.sh reduce-dhcp-t1   | sudo tee -a /var/log/ovn_migration_output.txt

2. Verify that the T1 parameter has propagated to existing VMs. The process might take up to four hours.

   • Log in to one of the Compute nodes.

   • Run tcpdump` over one of the VM taps attached to a project network.

     If T1 propagation is successful, expect to see requests occur approximately every 30 seconds:

     [heat-admin@overcloud-novacompute-0 ~]$ sudo tcpdump -i tap52e872c2-e6 port 67 or port 68 -n
     tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
     listening on tap52e872c2-e6, link-type EN10MB (Ethernet), capture size 262144 bytes
     13:17:28.954675 IP 192.168.99.5.bootpc > 192.168.99.3.bootps: BOOTP/DHCP, Request from fa:16:3e:6b:41:3d, length 300
     13:17:28.961321 IP 192.168.99.3.bootps > 192.168.99.5.bootpc: BOOTP/DHCP, Reply, length 355
     13:17:56.241156 IP 192.168.99.5.bootpc > 192.168.99.3.bootps: BOOTP/DHCP, Request from fa:16:3e:6b:41:3d, length 30013:17:56.249899 IP 192.168.99.3.bootps > 192.168.99.5.bootpc: BOOTP/DHCP, Reply, length 355

     Note

     This verification is not possible with cirros VMs. The cirros udhcpc` implementation does not respond to DHCP option 58 (T1). Try this verification on a port that belongs to a full Linux VM. Red Hat recommends that you check all the different operating systems represented in your workloads, such as variants of Windows and Linux distributions.

3. If any VM instances were not updated to reflect the change to the T1 parameter of DHCP, reboot them.

4. Lower the MTU of the pre-migration VXLAN networks:

   $ ovn_migration.sh reduce-mtu   | sudo tee -a /var/log/ovn_migration_output.txt

   This step reduces the MTU network by network and tags the completed network with adapted_mtu. The tool acts only on VXLAN networks. This step will not change any values if your deployment has only VLAN project networks.

5. If you have any instances with static IP assignment on VXLAN project networks, manually reduce the instance MTU by 8 bytes. For example, if the VXLAN-based MTU was 1450, change it to 1442.

   Note

   Perform this step only if you have manually provided static IP assignments and MTU settings on VXLAN project networks. By default, DHCP provides the IP assignment and MTU settings.

6. Proceed to Section 2.4, “Migrating the ML2 mechanism driver from OVS to OVN”..

Procedure

1. Stop all operations that interact with the Networking Service (neutron) API, such as creating new networks, subnets, routers, or instances, or migrating instances between compute nodes.

   Interaction with Networking API during migration can cause undefined behavior. You can restart the API operations after completing the migration.

2. Run ovn_migration.sh start-migration to begin the migration process. The tee command creates a copy of the script output for troubleshooting purposes.

   $ ovn_migration.sh start-migration  | sudo tee -a /var/log/ovn_migration_output.txt