Port Binding API

In the MidoNet integration with OpenStack, there are two ways a port could be bound:

• When a VM is launched, orchestrated by nova
• When an operator binds a virtual port to a specific host interface

This document describes the design of port binding in MidoNet that implements these use cases.

In the case of operator-specified port binding, there is a special case in which a port is bound to an interface connected to the uplink physical network, but that is not covered in this document.

Problem Description

MidoNet does not currently provide a way to bind ports in Neutron using standard Neutron API.

Proposed Change

Use the existing ‘binding’ extension API in Neutron to implement port binding in MidoNet.

To bind a port to a specific host interface, an operator makes a ‘create_port’ API request to Neutron and provide the following binding details:

• ‘binding:host_id’: ID of the host to bind the port on
• ‘binding:profile[“interface_name”]’: Name of the interface to bind the port

The host ID is stored in the ‘portbindings’ table, and the interface name is stored in the ‘midonet_portbindings’ table. When the host ID and the interface name are supplied in the port creation request, the MidoNet executes the binding within the same API request.

Updating a port with a different binding effectively unbinds the port and re-binds it to the new host interface.

In the case of VM port binding, the workflow is as follows:

1. Nova API makes a ‘create_port’ request to Neutron API specifying the ID of the host(‘host_id’) where the VM is going to be placed. ‘host_id’ is stored in Neutron’s ‘portbindings’ table.
2. Neutron generates the tap interface name the same way Nova does (‘tap’ + portID up to 14 chars), and stores it in the ‘midonet_portbindings’ table.
3. On the compute host, ‘mm-ctl’ script is executed to do the actual binding. ‘mm-ctl’ adds a port binding task to signal to MidoNet that the binding should occur. This step may change in the future.

For each scenario in which a port binding occurs, the plugin inserts a PORTBINDING task with ‘resource_id’ set to the ID of the port getting bound.

The actual mechanism in which the binding takes place inside MidoNet is outside the scope of this document.

REST API

An example of a port binding attributes in the request to create a port is:

{
  "binding:host_id": "HOST_ID",
  "binding:profile": {"interface_name": "eth0"}
}

DB Model

midonet_portbindings

Name	Type	Description
port_id	UUID	ID of the port
interface_name	String	Name of the interface to bind the port

‘port_id’ is the primary key and has a foreign key constraint to the ‘id’ column of the ‘ports’ table.

Client

The following command creates a port with port binding attributes:

neutron port-create [--binding:host_id HOST_ID]
                    [--binding:profile if_name=IF_NAME]

–binding:host_id HOST_ID:

ID of the host to bind the port on

–binding:profile if_name=IF_NAME:

Name of the interface to bind the port to