Strict minimum bandwidth support (egress)

Problem Description

RFE link:

Newton release added minimum bandwidth support to QoS policy rules. While this improvement works at the hypervisor level, it’s a best effort measure that will not prevent over-subscription on a specific network link bandwidth (When SUM i port[i].min_bw > max available bandwidth within a provider network).

NFV/Telcos are interested in these types of rules to make sure functions don’t over commit compute nodes.

Cloud Service Providers could make use of this feature to provide bandwidth guarantees for streaming.

Proposed Change

To provide a strict constraint we need scheduling cooperation with Nova through integration with the new Nova placement API [1][2].

Neutron L2 agents, or the specific plugin/backend will be responsible for registering per compute resources into the placement API. L2 agents are proposed to take this responsibility, since it mimics the design decision in Nova where nova-compute reports resources to such API. This has the benefit of distributing the workload across all the nodes instead having a central service responsible of syncing to the placement API.

The resources will have the following form, please note INGRESS is provided as a reference but it’s out of the scope of this spec:

NIC_BW_EGRESS.<physical-network> NIC_BW_INGRESS.<physical-network>

physical-network will be the “physnet” in the reference implementation, or “tunneling” in the case of requesting bandwidth on the tunneling path.

While modeling the tunneling bandwidth is not a simple thing, because it could vary based on host routers and interfaces, we will provide this simple model to start with.

Nova will use those details to count down and manage the inventories at its side.

When Nova creates, updates or gets a port, Neutron will show the resource counts needed by the port in the response, removing any dependency from Nova into the Neutron QoS policy rules:

{"port": {
    "status": "ACTIVE",
    "name": "",
    "device_id": "5e3898d7-11be-483e-9732-b2f5eccd2b2e",
    "resources": { "NIC_BW_EGRESS.ext-net": 1000, /*kbps*/
                   "NIC_BW_INGRESS.ext-net": 1000}

This extra dictionary could be incorporated to the QoS extension itself, but it makes sense to make something agnostic to the QoS extension that other resource aware extensions could make use of.

There is a common architecture in network configuration that we need to address. It’s very common to bond several interfaces, and pass each specific physnet or even tunneling through a VLAN on such bonding.

To properly handle that case is where we need to make virtual physnets handling the nesting, for example by providing a configuration like this per-agent:


virtual_physnets = bond0phys:bond0, bond1phys:bond1

nested_physnets = bond0phys:physnetA, bond0phys:physnetB, \
                  bond0phys:tunneling, \
                  bond1phys:physnetC, bond1phys:physnetD

In such case the <physical-network> part of the resources to nova would be substituted by bond0phys for physnetA / physnetB / tunneling and by bond1phys for physnetC and D.

The extra level of indirection is provided by virtual_physnets so interface name changes won’t de-sync the nova resources and allocations.

In this specific case, the total bandwidth will be collected from bond0 and bond1 and reported to NIC_BW_{EGRESS,INGRESS}.{bond0phys,bond1phys}, see work item 1.


We depend on several Nova changes which will allow the definition of custom resource classes [4].

Work Items

  1. Collecting available bandwidth from physnets on the agents with the ability to override bandwidth in config. Asignee: Rodolfo Alonso <>
  2. Write an API for sending collected bandwidth information to the Nova placement API. For the in-tree drivers this information can be sent right away from the agents to avoid the neutron-server bottleneck problem. But out-of-tree drivers would have the freedom to use such API from the QoS driver itself by, for example periodically syncing with the backend to grab bandwidth information. Or the out-of-tree drivers could choose to send the placement information from the backend itself to nova. Assignee: Miguel Lavalle
  3. Nova placement API client (custom resource classes [4]) Initial nova placement API client has already been merged [3] Assignee: Miguel Lavalle (he’s handling it for Routed Networks)
  4. Making the resources field available on port create/update/get for nova. Assignee: Slawek Kaplonski