Enable Neutron DVR on overcloud in TripleO


Neutron distributed virtual routing should be able to be configured in TripleO.

Problem Description

To be able to enable distributed virtual routing in Neutron there needs to be several changes to the current TripleO overcloud deployment. The overcloud compute node(s) are constructed with the neutron-openvswitch-agent image element, which provides the neutron-openvswitch-agent on the compute node. In order to support distributed virtual routing, the compute node(s) must also have the neutron-metadata-agent and neutron-l3-agent installed. The installation of the neutron-l3-agent and neutron-dhcp-agent will need also to be decoupled.

Additionally, for distributed virtual routing to be enabled, the neutron.conf, l3_agent.ini and ml2_conf.ini all need to have additional settings.

Proposed Change


In the tripleo-image-elements, move the current neutron-network-node element to an element named neutron-router, which will be responsible for doing the installation and configuration work required to install the neutron-l3-agent and the neutron-metadata-agent. This neutron-router element will list the neutron-openvswitch-agent in its element-deps. The neutron-network -node element will then become simply a ‘wrapper’ whose sole purpose is to list the dependencies required for a network node (neutron, neutron-dhcp-agent, neutron-router, os-refresh-config).

Additionally, in the tripleo-image-elements/neutron element, the neutron.conf, l3_agent.ini and plugins/ml2/ml2_conf.ini will be modified to add the configuration variables required in each to support distributed virtual routing (the required configuration variables are listed at https://wiki.openstack.org/wiki/Neutron/DVR/HowTo#Configuration).

In the tripleo-heat-templates, the nova-compute-config.yaml nova-compute-instance.yaml and overcloud-source.yaml files will be modified to provide the correct settings for the new distributed virtual routing variables. The enablement of distributed virtual routing will be determined by a ‘NeutronDVR’ variable which will be ‘False’ by default (distributed virtual routing not enabled) for backward compatibility, but can be set to ‘True’ if distributed virtual routing is desired.

Lastly, the tripleo-incubator script devtest_overcloud.sh will be modified to: a) build the overcloud-compute disk-image with neutron-router rather than with neutron-openvswitch-agent, and b) configure the appropriate parameter values to be passed in to the heat stack create for the overcloud so that distributed routing is either enabled or disabled.


We could choose to make no change to the neutron-router image-element and it can be included as well in the list of elements arguments to the disk image build for compute nodes. This has the undesired effect of also including/configuring and starting the neutron-dhcp-agent on each compute node. Alternatively, it is possible to keep the neutron-network-node element as it is and create a neutron-router element which is a copy of most of the element contents of the neutron-network-node element but without the dependency on the neutron-dhcp-agent element. This approach would introduce a significant amount of code duplication.

Security Impact

Although TripleO installation does not use FWaaS, enablement of DVR currently is known to break FWaaS. See https://blueprints.launchpad.net/neutron/+spec/neutron-dvr-fwaas

Other End User Impact

The user will have the ability to set an environment variable during install which will determine whether distributed virtual routing is enabled or not.

Performance Impact

None identified

Other Deployer Impact

The option to enable or disable distributed virtual routing at install time will be added. By default distributed virtual routing will be disabled.

Developer Impact

None identified



Primary assignee:

Erik Colnick (erikcolnick on Launchpad)

Other contributors:


Work Items

  • Create neutron-router element in tripleo-image-elements and move related contents from neutron-network-node element. Remove the neutron-dhcp-agent dependency from the element-deps of the neutron-router element.

  • Add the neutron-router element as a dependency in the neutron-network-node element-deps file. The element-deps file becomes the only content in the neutron-network-node element.

  • Add the configuration values indicated in https://wiki.openstack.org/wiki/Neutron/DVR/HowTo#Configuration to the neutron.conf, l3_agent.ini and ml2_conf.ini files in the neutron image element.

  • Add the necessary reference variables to the nova-compute-config.yaml and nova-compute-instance.yaml tripleo-heat-templates files in order to be able to set the new variables in the config files (from above item). Add definitions and default values in overcloud-source.yaml.

  • Modify tripleo-incubator devtest_overcloud.sh script to set the appropriate environment variables which will drive the configuration of neutron on the overcloud to either enable distributed virtual routers or disable distributed virtual routers (with disable as the default).




Existing TripleO CI will help ensure that as this is implemented, the current feature set is not impacted and that the default behavior of disabled distributed virtual routers is maintained.

Additional CI tests which test the installation with distributed virtual routers should be added as this implementation is completed.

Documentation Impact

Documentation of the new configuration option will be needed.