infix/doc/container.md

Containers in Infix

• Introduction
• Caution
• Getting Started
  • Examples
• Networking and Containers
  • Container Bridge
  • Container Host Interface
  • Host Networking
• Mounts and Volumes
  • Content Mounts
• Example Containers
  • System Container
  • Application Container: nftables
  • Application Container: ntpd
• Upgrading a Container Image

Introduction

Infix comes with native support for Docker containers using podman. The YANG model describes the current level of support, complete enough to run both system and application containers.

Key design features, like using Linux switchdev, allow users to assign switch ports directly to containers, not just bridged VETH pairs, this is a rare and in many cases unique feature of Infix.

All network specific settings are done using the IETF interfaces YANG model, with augments for containers to ensure smooth integration with container networking in podman.

Note: even though the podman command can be used directly from a shell prompt, we strongly recommend using the CLI commands instead. They employ the services of a wrapper container script which handles the integration of containers in the system.

Caution

A word of warning, containers can run on your system in privileged mode, as root. This gives them full access to devices on your system. But even when though unprivileged containers are fenced from the host with Linux namespaces, and resource limited using Linux cgroups, which scope container applications from seeing and accessing the complete system, there is no guarantee that an application cannot ever break out of this confinement.

• If the system is compromised, containers can be used to easily install malicious software in your system and over the network
• Your system is as secure as anything you run in the container
• If you run containers, there is no security guarantee of any kind
• Running 3rd party container images on your system could open a security hole/attack vector/attack surface
• An expert with knowledge how to build exploits will be able to jailbreak/elevate to root even if best practices are followed

This being said, a system suspected of being compromised can always be restored to a safe state with a factory reset. Provided, of course, that it has secure boot enabled.

Getting Started

In the CLI, containers can be run in one of two ways:

1. container run IMAGE [COMMAND], and
2. enter configure context, then edit container NAME

The first is useful mostly for testing, or running single commands in an image. It is a wrapper for podman run -it --rm ..., while the latter is a wrapper and adaptation of podman create ....

The second create a container with a semi-persistent writable layer that survives container restarts and host system restarts. However, if you change the container configuration or upgrade the image (see below), the container will be recreated and the writable layer is lost. This is why it is recommended to set up a named volume for directories, or use file [Content Mounts][], in your container you want truly persistent content.

In fact, in many cases the best way is to create a read-only container and use file mounts and volumes only for the critical parts. Podman ensures (using tmpfs) read-only containers still have writable directories for certain critical file system paths: /dev, /dev/shm, /run, /tmp, and /var/tmp. Meaning, what you most often need is writable volumes for /var/lib and /etc, or only file mounts for a few files in /etc. The actual needs depend on the container image and application to run.

Note: when running containers from public registries, double-check that they support the CPU architecture of your host system. Remember, unlike virtualization, containers reuse the host's CPU and kernel.

Examples

Classic Hello World:

admin@example-c0-ff-ee:/> container run docker://hello-world

Persistent web server using nginx, sharing the host's network:

admin@example-c0-ff-ee:/> configure
admin@example-c0-ff-ee:/config> edit container web
admin@example-c0-ff-ee:/config/container/web> set image docker://nginx:alpine
admin@example-c0-ff-ee:/config/container/web> set publish 80:80
admin@example-c0-ff-ee:/config/container/web> set network host
admin@example-c0-ff-ee:/config/container/web> leave
admin@example-c0-ff-ee:/> show container

Exit to the shell and verify the service with curl, or try to attach to your device's IP address using your browser:

admin@example-c0-ff-ee:~$ curl http://localhost

or connect to port 80 of your running Infix system with a browser. See the following sections for how to add more interfaces and manage your container at runtime.

Networking and Containers

By default, unlike other systems, persistent¹ containers have no networking enabled. All network access has to be set up explicitly. Currently two types of of container networks are supported:

• host: one end of a VETH pair, or a physical Ethernet port
• bridge: an IP masquerading bridge

For more information on VETH pairs, see the Networking Guide.

Container Bridge

A container bridge is what most container setups use and users want. The difference from a regular bridge is that the container runtime fully manages them -- connecting containers automatically with VETH pairs and setting up firewall rules between the host and other containers, as well as managing port forwarding. This transparent background management is what makes container use seem to be so simple.

All interface configuration is done in configure context.

admin@example-c0-ff-ee:/> configure
admin@example-c0-ff-ee:/config> edit interface docker0
admin@example-c0-ff-ee:/config/interface/docker0/> set container-network
admin@example-c0-ff-ee:/config/interface/docker0/> leave

There is more to this story. When using the CLI, and sticking to common interface nomenclature, Infix helps you with some of the boring stuff. E.g., creating a new interface with a name like brN or dockerN automatically infers the interface types, which you would otherwise have to set manually:

admin@example-c0-ff-ee:/config/interface/docker0/> set type bridge
admin@example-c0-ff-ee:/config/interface/docker0/> set container-network type bridge

Note: when doing the same operation over NETCONF there is no inference, so all the "magic" settings needs to be defined. This makes the CLI very useful for first setup and then extracting the resulting XML from the shell using the cfg -X command.

We have to declare the interface as a container network, ensuring the interface cannot be used by the system for any other purpose. E.g., a container host interface is supposed to be used by a container, by declaring it as such we can guarantee that it would never accidentally be added as a bridge or lag port. Hence, to move an interface currently set as a bridge-port it must be removed from the bridge before being given to a container.

The default subnet for a container bridge is 172.17.0.0/16, the bridge takes the .1 address and hand out the rest of the range to containers in a round-robin like fashion. A container with this network get an automatically created VETH pair connection to the bridge and a lot of other networking parameters (DNS, default route) are set up.

Some of the defaults of a container bridge can be changed, e.g., instead of set container-network type bridge, above, do:

admin@example-c0-ff-ee:/config/interface/docker0/> edit container-network
admin@example-c0-ff-ee:/config/interface/docker0/container-network/> set type bridge
admin@example-c0-ff-ee:/config/interface/docker0/container-network/> edit subnet 192.168.0.0/16
admin@example-c0-ff-ee:/config/interface/docker0/container-network/subnet/192.168.0.0/16/> set gateway 192.168.255.254
admin@example-c0-ff-ee:/config/interface/docker0/container-network/subnet/192.168.0.0/16/> end
admin@example-c0-ff-ee:/config/interface/docker0/container-network/> edit route 10.0.10.0/24
admin@example-c0-ff-ee:/config/interface/docker0/container-network/route/10.0.10.0/24/> set gateway 192.168.10.254
admin@example-c0-ff-ee:/config/interface/docker0/container-network/route/10.0.10.0/24/> end
admin@example-c0-ff-ee:/config/interface/docker0/container-network/> end
admin@example-c0-ff-ee:/config/interface/docker0/> leave

Other network settings, like DNS and domain, use built-in defaults, but can be overridden from each container. Other common settings per container is the IP address and name of the network interface inside the container. The default, after each stop/start cycle, or reboot of the host, is to name the interfaces eth0, eth1, in the order they are given in the network list, and to give the container the next address in a bridge. Below an example of a system container calls set network interface docker0, here we show how to set options for that network:

admin@example-c0-ff-ee:/config/container/ntpd/> edit network docker0 
admin@example-c0-ff-ee:/config/container/ntpd/network/docker0/> 
admin@example-c0-ff-ee:/config/container/ntpd/network/docker0/> set option 
<string>  Options for masquerading container bridges.
admin@example-c0-ff-ee:/config/container/ntpd/network/docker0/> help option 
NAME
        option <string>

DESCRIPTION
        Options for masquerading container bridges.

        Example: ip=1.2.3.4            -- request a specific IP (IPv4 or IPv6)
                 mac=00:01:02:c0:ff:ee -- set fixed MAC address in container
                 interface_name=foo0   -- set interface name inside container

admin@example-c0-ff-ee:/config/container/ntpd/network/docker0/> set option ip=172.17.0.2
admin@example-c0-ff-ee:/config/container/ntpd/network/docker0/> set option interface_name=wan
admin@example-c0-ff-ee:/config/container/ntpd/network/docker0/> leave

Container Host Interface

Another common use-case is to move a network interface into the network namespace of a container. Which the container bridge network type does behind the scenes with one end of the automatically created VETH pair. This works with regular Ethernet interfaces as well, but here we will use a VETH pair as an example along with a regular bridge (where other Ethernet interfaces may live as well).

admin@example-c0-ff-ee:/config/> edit interface veth0
admin@example-c0-ff-ee:/config/interface/veth0/> set veth peer ntpd
admin@example-c0-ff-ee:/config/interface/veth0/> set ipv4 address 192.168.0.1 prefix-length 24
admin@example-c0-ff-ee:/config/interface/veth0/> end
admin@example-c0-ff-ee:/config/> edit interface ntpd
admin@example-c0-ff-ee:/config/interface/ntpd/> set ipv4 address 192.168.0.2 prefix-length 24
admin@example-c0-ff-ee:/config/interface/ntpd/> set container-network

This is a routed setup, where we reserve 192.168.0.0/24 for the network between the host and the ntpd container. A perhaps more common case is to put veth0 as a port in a bridge with other physical ports. The point of the routed case is that port forwarding from the container in this case is limited to a single interface, not all interfaces as is the default in the masquerading container bridge setup.

Host Networking

The third use-case is host networking, this is where a container share the network namespace of the host. An example here could be a nftables or ntpd container -- single applications which add core functionality to the host operating system.

The host networking setup cannot be combined with any other network.

For an example, see below.

Mounts and Volumes

It is possible to mount files, directories, and even files matching a glob, into a container. This gives precise control over the container's file system:

admin@example-c0-ff-ee:/config/container/system/> edit mount leds
admin@example-c0-ff-ee:/config/container/system/mount/leds> set source /sys/class/leds
admin@example-c0-ff-ee:/config/container/system/mount/leds> set target /sys/class/leds
admin@example-c0-ff-ee:/config/container/system/mount/leds> end
admin@example-c0-ff-ee:/config/container/system/>

Sometimes volumes are a better fit. A volume is an automatically created read-writable entity that follows the life of your container.

admin@example-c0-ff-ee:/config/container/ntpd/> set volume varlib target /var/lib

Volumes survive reboots and upgrading of the base image, unlike the persistent writable layer you get by default, which does not survive upgrades. The volume is created by podman when the container first starts up, unlike a regular bind mount it synchronizes with the contents of the underlying container image's path on the first start. I.e., "bind-mount, if empty: then rsync".

Infix support named volumes (only), and it is not possible to share a volume between containers. All the tricks possible with volumes may be added in a later release.

Content Mounts

Content mount is a special type of where the file contents for the container is stored alongside the container configuration. This can be very useful when deploying similar systems at multiple sites. When the host loads its startup-config (or even factory-config) a temporary file is created using the decoded base64 data from the content node.

admin@example-c0-ff-ee:/config/container/ntpd/> edit mount ntpd.conf
admin@example-c0-ff-ee:/config/container/ntpd/mount/ntpd.conf> set content
... interactive editor starts up ...
admin@example-c0-ff-ee:/config/container/ntpd/mount/ntpd.conf> set target /etc/ntpd.conf
admin@example-c0-ff-ee:/config/container/ntpd/mount/ntpd.conf> end
admin@example-c0-ff-ee:/config/container/ntpd/>

The editor is a small Emacs clone called Mg, see the built-in help text, or press Ctrl-x Ctrl-c to exit and save. When the editor exits the contents are base64 encoded and stored in the candidate datastore.

Note: since these files are always recreated when the host is restarted, changes made by the container are not preserved, or saved back to the host's startup-config even if the read-only option is off.

Example Containers

System Container

Let's try out what we've learned by setting up a system container, a container providing multiple services, using the docker0 interface we created previously:

admin@example-c0-ff-ee:/> configure
admin@example-c0-ff-ee:/config> edit container system
admin@example-c0-ff-ee:/config/container/system/> set image ghcr.io/kernelkit/curios:edge
admin@example-c0-ff-ee:/config/container/system/> set network interface docker0
admin@example-c0-ff-ee:/config/container/system/> set publish 222:22
admin@example-c0-ff-ee:/config/container/system/> leave

Note: ensure you have a network connection to the registry. If the image cannot be pulled, creation of the container will be put in a queue and be retried every time there is a change in the routing table, e.g., default route is added.

Provided the image is downloaded successfully, a new system container now runs behind the docker0 interface, forwarding container port 22 to port 222 on all of the host's interfaces. (See help publish in the container configuration context for the full syntax.)

Available containers can be accessed from admin-exec:

admin@example-c0-ff-ee:/> show container
CONTAINER ID  IMAGE                          COMMAND     CREATED       STATUS       PORTS                 NAMES
439af2917b44  ghcr.io/kernelkit/curios:edge              41 hours ago  Up 16 hours  0.0.0.0:222->222/tcp  system

This is a system container, so you can "attach" to it by starting a shell (or logging in with SSH):

admin@example-c0-ff-ee:/> container shell system
root@439af2917b44:/#

Notice how the hostname inside the container changes. By default the container ID (hash) is used, but this can be easily changed:

root@439af2917b44:/# exit
admin@infix-00-00-00:/> configure
admin@infix-00-00-00:/config/> edit container system
admin@infix-00-00-00:/config/container/system/> set hostname sys101
admin@infix-00-00-00:/config/container/system/> leave
admin@infix-00-00-00:/> container shell system
root@sys101:/#

Application Container: nftables

Infix currently does not have a native firewall configuration, and even when it does it will never expose the full capabilities of nftables. For really advanced setups, the following will be the only alternative:

admin@example-c0-ff-ee:/> configure
admin@example-c0-ff-ee:/config> edit container nftables
admin@example-c0-ff-ee:/config/container/system/> set image ghcr.io/kernelkit/curios-nftables:edge
admin@example-c0-ff-ee:/config/container/system/> set network host
admin@example-c0-ff-ee:/config/container/system/> edit mount nftables.conf
admin@example-c0-ff-ee:/config/container/system/mount/nftables.conf/> set target /etc/nftables.conf
admin@example-c0-ff-ee:/config/container/system/mount/nftables.conf/> set content
... interactive editor starts up where you can paste your rules ...
admin@example-c0-ff-ee:/config/container/system/mount/nftables.conf/> leave

Application Container: ntpd

The default NTP server/client in Infix is Chrony, a fully working and capable workhorse for most use-cases. However, it does not support a feature like multicasting, for that you need ISC ntpd.

As we did with nftables, previously, we can use host networking and set up a read-only config file that is bind-mounted into the container's file system and store in the host's startup-config. However, ntpd also saves clock drift information in /var/lib/ntpd, so we will also use volumes in this example.

admin@example-c0-ff-ee:/> configure
admin@example-c0-ff-ee:/config> edit container ntpd
admin@example-c0-ff-ee:/config/container/ntpd/> set image ghcr.io/kernelkit/curios-ntpd:edge
admin@example-c0-ff-ee:/config/container/ntpd/> set network interface ntpd    # From veth0 above
admin@example-c0-ff-ee:/config/container/ntpd/> edit mount ntp.conf
admin@example-c0-ff-ee:/config/container/ntpd/mount/ntp.conf/> set target /etc/ntp.conf
admin@example-c0-ff-ee:/config/container/ntpd/mount/ntp.conf/> set content
... interactive editor starts up where you can paste your rules ...
admin@example-c0-ff-ee:/config/container/ntpd/mount/ntp.conf/> end
admin@example-c0-ff-ee:/config/container/ntpd/> edit volume varlib
admin@example-c0-ff-ee:/config/container/ntpd/volume/varlib/> set target /var/lib
admin@example-c0-ff-ee:/config/container/ntpd/volume/varlib/> leave
admin@example-c0-ff-ee:/> copy running-config startup-config

The ntp.conf file is stored in the host's startup-config and any state data in the container's /var/lib is retained between reboots and across image upgrades.

Upgrading a Container Image

All container configurations are locked to the image hash at the time of first download, not just ones that use an :edge or :latest tag. An upgrade of containers using versioned images is more obvious -- update the configuration -- but the latter is a bit trickier. Either remove the configuration and recreate it (leave/apply the changes between), or use the admin-exec level command:

admin@example-c0-ff-ee:/> container upgrade NAME

Where NAME is the name of your container. This command stops your container, does a container pull IMAGE, and then recreates the container with the new image. Upgraded containers are not automatically restarted.

admin@example-c0-ff-ee:/> container start NAME

Note: the default writable layer is lost when upgrading the image Use named volumes for directories with writable content you wish to keep over an upgrade.

---

1. this does not apply to the admin-exec command container run. This command is intended to be used for testing and evaluating container images. Such containers are given a private network behind an IP masquerading bridge. ↩︎