charm-specs/specs/rocky/implemented/neutron-dynamic-routing.rst

Neutron Dynamic Routing

OpenStack supports dynamic routing, specifically BGP. BGP forms a significant part of the routing infrastructure for many TelCos and large other organizations with complex networks. Our charms need to grow support for dynamic routing.

Problem Description

In a typical setup with Neutron Gateway, infrastructure routers do not have knowledge of the private networks allocated to OpenStack tenants. As a result, services external to OpenStack do not know how to route traffic to OpenStack instances. As OpenStack networks are elastic and therefore can evolve in many ways, a way of communicating changes between OpenStack and external routers is needed.

Since networks in OpenStack are self serviced, any addition or removal of OpenStack network should not depend on network administrator’s actions. Network limitations should be set up front. This is further facilitated by the use of subnet pools in OpenStack.

Other implications include decoupling subnets from layer 2, allowing different next-hops for floating IPs.

Proposed Change

Neutron dynamic routing solves this problem by introducing a BGP speaker, which then peers with the existing infrastructure router(s) and announces the next-hop virtual routers for OpenStack owned networks. This allows dynamic routing changes to be communicated to the physical infrastructure based on changes in OpenStack networks. Since OpenStack Networks are managed by users, address scope limitations need to be in place.

A new charm is proposed called neutron-dynamic-routing which will configure and deploy the neutron-bgp-dragent (Neutron BGP dynamic routing agent). The neutron-bgp-dragent is a BGP speaker which can be peered with existing routers in the BGP infrastructure. This charm will require interfaces for AMQP and potentially neutron-api-plugin (TBD). For testing purposes it will also make use of the bgp interface to peer with the quagga charm, both written by Frode Nordahl (See Testing below.)

Requirements

The charm will need to select an interface on the provider network for communication with OpenStack. It may also need to select an interface to speak with BGP routers in the infrastructure.

High availability is accomplished by deploying N number of units of neutron-dynamic-routing with care for placement on different physical hosts. This will introduce multiple neutron-bgp-dragents. BGP infrastructure routers will need to be manually informed of each neutron-bgp-dragent.

IPv4 and IPv6 support is handled with separate bgp-speakers defined for each.

The charm will need to support both DVR and centralized OpenStack routing.

Outside the scope

It is important to understand what the OpenStack dynamic routing implementation does not do and lies outside of the scope of this spec.

• It does not provide ingress BGP to OpenStack, it is purely egress advertisement of OpenStack owned networks.
• It does not automatically advertise all OpenStack networks or whole subnet pools. A considerable amount of administrator configuration is still required, including associating OpenStack networks with the bgp-speaker. See the Testing documentation https://docs.openstack.org/neutron-dynamic-routing/latest/contributor/testing.html>__ for a sense of the administrative overhead required.
• It does not provide a mechanism for injecting arbitrary BGP routes (for example for /32 FIPs). It merely advertises OpenStack networks that have been associated with the bgp speaker.

Alternatives

Floating IPs, and NAT in general, are one approach to this problem, but there are couple of drawbacks. For starters, NAT comes with a performance price as number of connections grows. In cloud, where many VMs can establish connections to various external peers, this can require significant memory and cpu resources. Neutron gateway doesn't really scale without manual intervention. On top of that, if only NAT is used, peers can’t really know which instance established connection, they only know connection came ‘from the cloud’. Same problems apply to DVR.

Static routes on physical gateways are the closest thing to BGP solution. The only drawback is operational; in case address scope in Neutron changes, these changes need to be implemented on physical routers too.

Implementation

Assignee(s)

Primary assignee:

thedac

Additional work:

fnordahl

Gerrit Topic

Use Gerrit topic "<topic_name>" for all patches related to this spec.

git-review -t dragent

Work Items

New charm neutron-dynamic-routing

A new reactive charm will be developed to configure and deploy the neutron-bgp-dragent.

Update neutron-api charm

The neutron-api charm will need to load the service_plugin neutron_dynamic_routing.services.bgp.bgp_plugin.BgpPlugin and subsequently run a db migrate.

Potential need for new neutron-api-plugin interface

It is unclear at this time if a relationship to neutron-api will be required. If it is required no layered interface for neutron-api-plugin yet exists and will need to be created.

New charm quagga

For testing purposes the new quagga charm will act as a BGP peer to validate and test neutron-dynamic-routing. Frode Nordahl has already begun work on this project: https://github.com/openstack-charmers/charm-quagga

New interface bgp

For testing purposes the new bgp interface will define the peering relationship between neutron-dynamic-routing and the quagga charm. Frode Nordahl has already begun work on this project: https://github.com/openstack-charmers/interface-bgp

Repositories

A new repository for the neutron-dynamic-routing charm is needed.

https://git.openstack.org/openstack/charm-neutron-dynamic-routing

A new repository for the quagga charm is needed.

https://git.openstack.org/openstack-charmers/charm-quagga

A new repository for the bgp interface is needed.

https://git.openstack.org/openstack-charmers/interface-bgp

Documentation

An update to the charm deployment guide will be required.

Upstream documentation is found at the following: https://docs.openstack.org/neutron-dynamic-routing/latest/

Security

The neutron-dynamic-routing charm is dependent on the OpenStack implementation of BGP. Which uses a simple string as a password.

Testing

The neutron-dynamic-routing charm will need to be tested with a BGP peer. Frode Nordahl has begun work on the quagga charm which will act as an infrastructure BGP router allowing for testing and validation.

A mojo spec, or other suitably automated test, will be a requirement for this feature implementation.

Dependencies

None