Alpy

Test network virtual appliance using Docker containers

This project is a Python library for testing network virtual appliances.

The appliance being tested is referred to as a device under test or DUT.

This repository includes scripts and modules to build a simple appliance called Rabbit. Rabbit is Alpine Linux with a few packages pre-installed. Having this simple DUT allows to quickly test the alpy library and to demonstrate its features.

The tests for the Rabbit device share a lot of code so the code is organized as a library. The library is called carrot.

Network design

The DUT communicates with containers attached to each of its network links.

Guest network adapters are connected to the host via tap devices (Figure 1).

+-----QEMU hypervisor------+
|                          |   +-------------+
| +-----Guest OS-----+     |   |             |
| |                  |     |   |  docker     |
| | +--------------+ |     |   |  container  |
| | |              | |     |   |  network    |
| | |  NIC driver  | |     |   |  namespace  |
| | |              | |     |   |             |
| +------------------+     |   |   +-----+   |
|   |              |       |   |   |     |   |
|   | NIC hardware +---+-----------+ tap |   |
|   |              |   |   |   |   |     |   |
|   +--------------+   |   |   |   +-----+   |
|                      |   |   |             |
+--------------------------+   +-------------+
                       |
                       |
                       v
                 +-----------+
                 |           |
                 | pcap file |
                 |           |
                 +-----------+

Figure 1. Network link between QEMU guest and a docker container.

Each tap device lives in its network namespace. This namespace belongs to a dedicated container - a node. The node's purpose is to keep the namespace alive during the lifetime of a test.

For an application to be able to communicate with the DUT the application is containerized. The application container must be created in a special way: it must share network namespace with one of the nodes.

Figure 2 shows an example where application containers app0 and app1 share network namespace with node container node0. Application container app2 shares another network namespace with node2.

This sharing is supported by Docker. All we have to do is to create the application container with the --network=container:NODE_NAME Docker option. For example, if we want to send traffic to the DUT via its first link, we create a traffic generator container with Docker option --network=container:node0.

+----QEMU---+   +------shared network namespace-----+
|           |   |                                   |
|           |   |    eth0                           |
|   +---+   |   |   +---+   +-----+ +----+ +----+   |
|   |NIC+-----------+tap|   |node0| |app0| |app1|   |
|   +---+   |   |   +---+   +-----+ +----+ +----+   |
|           |   |                                   |
|           |   +-----------------------------------+
|           |
|           |
|           |
|           |   +------shared network namespace-----+
|           |   |                                   |
|           |   |    eth0                           |
|   +---+   |   |   +---+   +-----+                 |
|   |NIC+-----------+tap|   |node1|                 |
|   +---+   |   |   +---+   +-----+                 |
|           |   |                                   |
|           |   +-----------------------------------+
|           |
|           |
|           |
|           |   +------shared network namespace-----+
|           |   |                                   |
|           |   |    eth0                           |
|   +---+   |   |   +---+   +-----+ +----+          |
|   |NIC+-----------+tap|   |node2| |app2|          |
|   +---+   |   |   +---+   +-----+ +----+          |
|           |   |                                   |
+-----------+   +-----------------------------------+

Figure 2. Application containers attached to the DUT links.

Author

Alexey Bogdanenko

License

Alpy is licensed under:

SPDX-License-Identifier: GPL-3.0-or-later

See COPYING for more details.