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Description:

alpy 3.0.0

Test network virtual appliance using Docker containers

Contents

General information

The project
Author
License
Description

Examples
Features

The simplest docker to QEMU networking connection
Reliable packet capture
First-class Docker container support
Logging
No trash left behind
No root required

API documentation
Network design
Building a network of nodes
FAQ

How do I watch serial console?
How do I watch traffic on an interface?
Can I use Wireshark to watch traffic on an interface?
How do I debug my program?
How do I enter node network namespace?

A note about GitLab Container Registry
Related projects

General information

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

Author
Alexey Bogdanenko

License
Alpy is licensed under SPDX-License-Identifier: GPL-3.0-or-later. See
COPYING for more details.

Description
Alpy manages containers via Docker Python API.
Alpy interacts with QEMU using Python API of the QEMU Monitor Protocol
(QMP). QMP is a JSON-based protocol that allows applications to communicate with
a QEMU instance.
Alpy gives user Pexpect object to interact with a serial console. The Pexpect
object is configured to log console input and output via the standard logging
module.
Alpy is packaged and deployed to PyPI. The package can be installed using
pip.
There are unit tests (pytest) and integration tests in GitLab CI pipeline.
Alpy is tested and works on the latest Ubuntu and the latest Ubuntu LTS release.

Examples
The alpy library 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 demonstrate the library
features and capabilities. The tests verify a few features of the network
appliance, for example:

IPv4 routing (see rabbit/tests/forward-ipv4/main.py)
rate-limiting network traffic (see rabbit/tests/rate-limit/main.py)
load-balancing HTTP requests (see rabbit/tests/load-balancing/main.py)

The tests are executed automatically in the GitLab CI pipeline.
Example network (test rate-limit):
+-------------------------------------+
| |
| Device under test |
| rate limit = 1mbps |
+-------+--------------------+--------+
| |
| |
| |
+-------+--------+ +-------+--------+
| | | |
| 192.168.1.1/24 | | 192.168.1.2/24 |
| | | |
| node0 | | node1 |
| iperf3 client | | iperf3 server |
+----------------+ +----------------+
Example test output:
INFO __main__ Test description: Check that rabbit rate-limits traffic.
INFO alpy.node Create tap interfaces...
INFO alpy.node Create tap interfaces... done
INFO alpy.qemu Initialize QMP monitor...
INFO alpy.qemu Initialize QMP monitor... done
INFO alpy.qemu Start QEMU...
INFO alpy.qemu Start QEMU... done
INFO alpy.qemu Accept connection from QEMU to QMP monitor...
INFO alpy.qemu Accept connection from QEMU to QMP monitor... done
INFO alpy.node Create nodes...
INFO alpy.node Create nodes... done
INFO alpy.console Connect to console...
INFO alpy.console Connect to console... done
INFO alpy.utils Enter test environment
INFO __main__ Start iperf3 server on node 1...
INFO __main__ Start iperf3 server on node 1... done
INFO alpy.qemu Start virtual CPU...
INFO alpy.qemu Start virtual CPU... done
INFO alpine Wait for the system to boot...
INFO alpine Wait for the system to boot... done
INFO alpine Login to the system...
INFO alpine Login to the system... done
INFO alpy.remote_shell Type in script configure-rabbit...
INFO alpy.remote_shell Type in script configure-rabbit... done
INFO alpy.remote_shell Run script configure-rabbit...
INFO alpy.remote_shell Run script configure-rabbit... done
INFO __main__ Start iperf3 client on node 0...
INFO __main__ Measure rate...
INFO __main__ Measure rate... done
INFO __main__ Parse iperf3 report...
INFO __main__ Parse iperf3 report... done
INFO __main__ Start iperf3 client on node 0... done
INFO alpine Initiate system shutdown...
INFO alpine Initiate system shutdown... done
INFO alpy.qemu Wait until the VM is powered down...
INFO alpy.qemu Wait until the VM is powered down... done
INFO alpy.qemu Wait until the VM is stopped...
INFO alpy.qemu Wait until the VM is stopped... done
INFO __main__ Rate received, bits per second: 976321
INFO __main__ Check rate...
INFO __main__ Check rate... done
INFO alpy.utils Exit test environment with success
INFO alpy.console Close console...
INFO alpy.console Close console... done
INFO alpy.qemu Quit QEMU...
INFO alpy.qemu Quit QEMU... done
INFO alpy.utils Test passed
The tests for the Rabbit device share a lot of code so the code is organized as
a library. The library is called carrot.

Features

The simplest docker to QEMU networking connection
Nothing in the middle. No bridges, no veth pairs, no NAT etc.
Each layer 2 frame emitted is delivered unmodified, reliably.

Reliable packet capture
Each frame is captured reliably thanks to the QEMU filter-dump feature.

First-class Docker container support
Alpy follows and encourages single process per container design.

Logging
Test logs are easy to configure and customize. Alpy consistently uses Python
logging module.
Alpy collects serial console log in binary as well as text (escaped) form.

No trash left behind
Alpy cleans up after itself:

processes stopped with error codes and logs collected,
files, directories unmounted,
temporary files removed,
sockets closed,
interfaces removed…

… reliably.

No root required
Run as a regular user.

API documentation
The documentation is published on GitLab Pages of your GitLab project (if GitLab
Pages is enabled on your GitLab instance). For example, upstream project
documentation lives at https://abogdanenko.gitlab.io/alpy.
Alpy API documentation is generated using Sphinx. To generate HTML API
documentation locally, install Sphinx package and run the following
command:
PYTHONPATH=. sphinx-build docs public
To view the generated documentation, open public/index.html in a browser.

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

Building a network of nodes
Network configuration operations are performed by temporary one-off Docker
containers by calling ip commands inside the containers.
A distinction is made between a simplified version of the ip binary and the
full version. The simplified version is a busybox applet. The full version is
shipped in the iproute2 package.
Here is a list of features which alpy requires but which are missing from the
simplified version:

Move a network interface to a different namespace (“ip link set netns …”)
Create a tap interface (“ip tuntap add mode tap …”)

The image which contains the simplified version is called busybox_image while
the full image is called iproute2_image.
The images must be provided by the caller and must be present on the system. For
example, set:
busybox_image = "busybox:latest"
iproute2_image = "registry.gitlab.com/abogdanenko/alpy/iproute2:latest"

FAQ

How do I watch serial console?
Use tail:
tail --follow name --retry console.log
The same command, but shorter:
tail -F console.log

How do I watch traffic on an interface?
Use tcpdump:
tail --bytes +0 --follow name --retry link0.pcap | tcpdump -n -r -
The same command, but shorter:
tail -Fc +0 link0.pcap | tcpdump -nr-

Can I use Wireshark to watch traffic on an interface?
Yes, you can:
tail --bytes +0 --follow name --retry link0.pcap | wireshark -k -i -
The same command, but shorter:
tail -Fc +0 link0.pcap | wireshark -ki-

How do I debug my program?
Use The Python Debugger.

How do I enter node network namespace?

Get node pid:
docker inspect --format '{{.State.Pid}}' node0

Jump into node namespace using that pid:
nsenter --net --target "$pid"

One-liner:
nsenter --net --target "$(docker inspect --format '{{.State.Pid}}' node0)"

A note about GitLab Container Registry
Many CI jobs use one of the custom images built on the “build-docker-images”
stage. The images are stored in the GitLab Container Registry.
The images are pulled from locations specified by GitLab variables. By default,
the variables point to the registry of the current GitLab project.
If you forked this project and GitLab Container Registry is disabled in your
project, override the variables on a project level so that the images are pulled
from some other registry.
For example, set
IMAGE_UBUNTU_LTS=registry.gitlab.com/abogdanenko/alpy/ubuntu-lts:latest.

Related projects

Containernet
Kathara
Netkit
GNS3
Virtual Networks over linuX (VNX)
Pipework: Software-Defined Networking for Linux Containers
Eve-NG