Docker Containers

A network operating system for switches and routers, that runs Docker?

Yes, as of Infix v24.02 support for running containers using podman is supported. Because networking is a first class citizen in Infix, you can set up quite advanced virtual topologies with containers. This blog post is the first in a series of posts that aims to show this.

This post assumes knowledge and familiarity with the Infix Network Operating System. Ensure you have either a network connection or console access to your Infix system and can log in to it using SSH. Recommended reading includes the networking documentation.

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Introduction

All configuration and administration of networking and containers is done through the CLI:

admin@infix:~$ cli

See the 'help' command for an introduction to the system

admin@infix:/>

Notice the slight change in the prompt. Return to the Bash shell using the exit command, or Ctrl-D, from the “admin-exec” top level of the CLI.

Networking Basics

In Infix all network access has to be set up explicitly, so there is no default container networking setup (it’s a security thing). There are two types available to choose from:

• host: Ethernet interface
• bridge: Masquerading bridge

The first can be any physical port/interface which is handed over to the container or, more commonly, one end of a VETH pair.

The latter type is usually available as docker0, or podman0, on your host system. These bridges are managed by the container runtime, in the case of Infix this is podman. When a container is set to a container bridge network, a VETH pair is automatically created when the container is started – one end is attached to the bridge and the other connected to the container as a regular interface.

Here’s how you create a container bridge:

admin@infix:/> configure
admin@infix:/config> edit interface docker0
admin@infix:/config/interface/docker0> set container-network
admin@infix:/config/interface/docker0> leave

Web Server Container

Now, time for a basic web server example. For our first container we’ll be using docker://nginx:alpine. It’s a relatively small container with the Nginx web server built on top of the Alpine Linux image.

admin@infix:/> configure
admin@infix:/config> edit container web
admin@infix:/config/container/web/> set image docker://nginx:alpine
admin@infix:/config/container/web/> edit network
admin@infix:/config/container/web/network/> set interface docker0
admin@infix:/config/container/web/network/> set publish 8080:80
admin@infix:/config/container/web/network/> leave

Issuing the command leave queues a job to download the image and create a container in the background. To see the progress:

admin@infix:/> show log container

or just poll the status command:

admin@infix:/> show container
CONTAINER ID  IMAGE                           COMMAND               CREATED         STATUS         PORTS               NAMES
c60a6deeea4e  docker.io/library/nginx:alpine  nginx -g daemon o...  2 minutes ago   Up 2 minutes   0.0.0.0:8080->80/tcp  web

You should now be able to access the web server on port 8080 of the host’s IP address.

Nginx default landing page.

Customizing Content

Deceivingly enough, Docker containers have a thin writable layer that allows changing just about any file in the image. The big HOWEVER though is that this layer doesn’t survive configuration changes or, most importantly, image upgrades.

Use Volumes! They are a specialized type of “mount”, for people familiar with UNIX systems. Infix currently supports named mounts that provide a persistent writable layer for containers.

Here’s how to add a volume to your container:

admin@infix:/> configure
admin@infix:/config/> edit container web
admin@infix:/config/container/web/> edit volume content
admin@infix:/config/container/web/volume/content/> set target /usr/share/nginx/html
admin@infix:/config/container/web/volume/content/> leave

Named volumes have the downside of being opaque to the host, so the easiest is to upload the content using scp or editing it directly in the container:

admin@infix:/> container shell web
d95ce9f7674d:/# vi /usr/share/nginx/html/
50x.html    index.html
d95ce9f7674d:/# vi /usr/share/nginx/html/index.html 
... edit, save & exit from vi ...
d95ce9f7674d:/# 

Container Content in Device Configuration

Save the best for last? A neat feature is that container content can be saved in the system’s startup-config and therefore be automatically be backed up by administrators snapshotting the system.

This also means that custom(er) builds of Infix can bundle a built-in container’s initial configuration in the Infix factory-config, which can be very useful when deploying at new installations.

This feature is perfectly suited for container applications that need a specific site setup. For example a configuration file. Here we use the same container image to bundle an index.html file:

admin@infix:/> configure
admin@infix:/config/> edit container web
admin@infix:/config/container/web/> edit mount index.html
admin@infix:/config/container/web/mount/index.html/> set target /usr/share/nginx/html/index.html
admin@infix:/config/container/web/mount/index.html/> text-editor content

The content setting is an alternative to source for file mounts which allows providing the contents through the device’s configuration.

The text-editor command can be changed to use other editors in the system configuration context, by default it starts a Micro Emacs clone, Mg. See the documentation for more information.

Paste in this:

<!DOCTYPE html>
<html>
<head>
<title>Welcome to Infix!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to Infix the Network Operating System!</h1>
<p>If you see this page, the nginx web server container has been
installed and is working.</p>

<p>For online documentation and support please refer to the
<a href="https://kernelkit.github.io/">Infix Homepage</a>.<br/>

Commercial support and customer adaptations are available from
<a href="https://addiva.se/electronics">Addiva Elektronik AB</a>.</p>

<p><em>Thank you for reading this blog post!</em></p>
</body>
</html>

Save and exit with the usual Emacs salute: C-x C-x (Ctrl-X Ctrl-c, or hold down Ctrl while tapping the X and C keys).

Leave configuration context to activate your changes:

admin@infix:/config/container/web/mount/index.html/> leave

Reload your browser to see the change.

Fin

That’s the end of the first post about containers in Infix. Remember to save your changes for next boot:

admin@infix:/> copy running-config startup-config

Take care! <3