Install and Configure FRRouter

The goal of this spec is to design and plan requirements for adding support to TripleO to install and provide a basic configuration of Free Range Router (FRR) on overcloud nodes in order to support BGP dynamic routing. There are multiple reasons why an administrator might want to run FRR, including to obtain multiple routes on multiple uplinks to northbound switches, or to advertise routes to networks or IP addresses via dynamic routing protocols.

Problem description

There are several use cases for using BGP, and in fact there are separate efforts underway to utilize BGP for the control plane and data plane.

BGP may be used for equal-cost multipath (ECMP) load balancing of outbound links, and bi-directional forwarding detection (BFD) for resiliency to ensure that a path provides connectivity. For outbound connectivity BGP will learn routes from BGP peers.

BGP may be used for advertising routes to API endpoints. In this model HAProxy will listen on an IP address and FRR will advertise routes to that IP to BGP peers. High availability for HAProxy is provided via other means such as Pacemaker, and FRR will simply advertise the virtual IP address when it is active on an API controller.

BGP may also be used for routing inbound traffic to provider network IPs or floating IPs for instance connectivity. The Compute nodes will run FRR to advertise routes to the local VM IPs or floating IPs hosted on the node. FRR has a daemon named Zebra that is responsible for exchanging routes between routing daemons such as BGP and the kernel. The redistribute connected statement in the FRR configuration will cause local IP addresses on the host to be advertised via BGP. Floating IP addresses are attached to a loopback interface in a namespace, so they will be redistributed using this method. Changes to OVN will be required to ensure provider network IPs assigned to VMs will be assigned to a loopback interface in a namespace in a similar fashion.

Proposed Change

Overview

Create a container with FRR. The container will run the BGP daemon, BFD daemon, and Zebra daemon (which copies routes to/from the kernel). Provide a basic configuration that would allow BGP peering with multiple peers. In the control plane use case the FRR container needs to be started along with the HA components, but in the data plane use case the container will be a sidecar container supporting Neutron. The container is defined in a change proposed here: 1

The container will be deployed using a TripleO Deployment Service. The service will use Ansible to template the FRR configuration file, and a simple implementation exists in a proposed change here: 2

The current FRR Ansible module is insufficient to configure BGP parameters and would need to be extended. At this time the Ansible Networking development team is not interested in extending the FRR module, so the configuration will be provided using TripleO templates for the FRR main configuration file and daemon configuration file. Those templates are defined in a change proposed here: 3

A user-modifiable environment file will need to be provided so the installer can provide the configuration data needed for FRR (see User Experience below).

OVN will need to be modified to enable the Compute node to assign VM provider network IPs to a loopback interface inside a namespace. These IP address will not be used for sending or receiving traffic, only for redistributing routes to the IPs to BGP peers. Traffic which is sent to those IP addresses will be forwarded to the VM using OVS flows on the hypervisor. An example agent for OVN has been written to demonstrate how to monitor the southbound OVN DB and create loopback IP addresses when a VM is started on a Compute node. The OVN changes will be detailed in a separate OVN spec. Demonstration code is available on Github: 4

User Experience

The installer will need to provide some basic information for the FRR configuration, including whether to enable BFD, BGP IPv4, BGP IPv6, and other settings. See the Example Configuration Data section below.

Additional user-provided data may include inbound or outbound filter prefixes. The default filter prefixes will accept only default routes via BGP, and will export only loopback IPs, which have a /32 subnet mask for IPv4 or /128 subnet mask for IPv6.

Example Configuration Data

tripleo_frr_bfd: false
tripleo_frr_bgp: false
tripleo_frr_bgp_ipv4: true
tripleo_frr_bgp_ipv4_allowas_in: false
tripleo_frr_bgp_ipv6: true
tripleo_frr_bgp_ipv6_allowas_in: false
tripleo_frr_config_basedir: "/var/lib/config-data/ansible-generated/frr"
tripleo_frr_hostname: "{{ ansible_hostname }}"
tripleo_frr_log_level: informational
tripleo_frr_watchfrr: true
tripleo_frr_zebra: false

Alternatives

  1. Routing outbound traffic via multiple uplinks

    Fault-tolerance and load-balancing for outbound traffic is typically provided by bonding Ethernet interfaces. This works for most cases, but is susceptible to unidirectional interface failure, a situation where traffic works in only one direction. The LACP protocol for bonding does provide some protection against unidirectional traffic failures, but is not as robust as bi-directional forwarding detection (BFD) provided by FRR.

  2. Routing inbound traffic to highly-available API endpoints

    The most common method currently used to provide HA for API endpoints is to use a virtual IP that fails over from active to standby nodes using a shared Ethernet MAC address. The drawback to this method is that all standby API controllers must reside on the same layer 2 segment (VLAN) as the active controller. This presents a challenge if the operator wishes to place API controllers in different failure domains for power and/or networking. A BGP daemon avoids this limitation by advertising a route to the shared IP address directly to the BGP peering router over a routed layer 3 link.

  3. Routing to Neutron IP addresses

    Data plane traffic is usually delivered to provider network or floating IP addresses via the Ethernet MAC address associated with the IP and determined via ARP requests on a shared VLAN. This requires that every Compute node which may host a provider network IP or floating IP has the appropriate VLAN trunked to a provider bridge attached to an interface or bond. This makes it impossible to migrate VMs or floating IPs across layer 3 boundaries in edge computing topologies or in a fully layer 3 routed datacenter.

Security Impact

There have been no direct security impacts identified with this approach. The installer should ensure that security policy on the network as whole prevents IP spoofing which could divert legitimate traffic to an unintended host. This is a concern whether or not the OpenStack nodes are using BGP themselves, and may be an issue in environments using traditional routing architecture or static routes.

Upgrade Impact

When (if) we remove the capability to manage network resources in the overcloud heat stack, we will need to evaluate whether we want to continue to provide BGP configuration as a part of the overcloud configuration.

If an operator wishes to begin using BGP routing at the same time as upgrading the version of OpenStack used they will need to provide the required configuration parameters if they differ from the defaults provided in the TripleO deployment service.

Performance Impact

No performance impacts are expected, either positive or negative by using this approach. Attempts have been made to minimize memory and CPU usage by using conservative defaults in the configuration.

Documentation Impact

This is a new TripleO deployment service and should be properly documented to instruct installers in the configuration of FRR for their environment.

The TripleO docs will need updates in many sections, including:

The FRR daemons are documented elsewhere, and we should not need to document usage of BGP in general, as this is a standard protocol. The configuration of top-of-rack switches is different depending on the make and model of routing switch used, and we should not expect to provide configuration examples for network hardware.

Implementation

The implementation will require a new TripleO deployment service, container definition, and modifications to the existing role definitions. Those changes are proposed upstream, see the References section for URL links.

Assignee(s)

Primary assignee:
  • Dan Sneddon

Secondary assignees:
  • Michele Baldessari

  • Carlos Gonclaves

  • Daniel Alvarez Sanchez

  • Luis Tomas Bolivar

Work Items

  • Develop the container definition

  • Define the TripleO deployment service templates

  • Define the TripleO Ansible role

  • Modify the existing TripleO roles to support the above changes

  • Merge the changes to the container, deployment service, and Ansible role

  • Ensure FRR packages are available for supported OS versions

References

1

Review: DNR/DNM Frr support.

2

Review: Add tripleo_frr role.

3

Review: WIP/DNR/DNM FRR service.

4

OVN BGP Agent.