Containers in Infix =================== * [Introduction](#introduction) * [Caution](#caution) * [Getting Started](#getting-started) * [Examples](#examples) * [Networking and Containers](#networking-and-containers) * [Container Bridge](#container-bridge) * [Container Host Interface](#container-host-interface) * [Host Networking](#host-networking) * [Mounts and Volumes](#mounts-and-volumes) * [Content Mounts](#content-mounts) * [Example Containers](#example-containers) * [System Container](#system-container) * [Application Container: nftables](#application-container--nftables) * [Application Container: ntpd](#application-container--ntpd) * [Upgrading a Container Image](#upgradeing-a-container-image) Introduction ------------ Infix comes with native support for Docker containers using [podman][]. The [YANG model][1] 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, persistent[^1] 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][0]. ### 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 Options for masquerading container bridges. admin@example-c0-ff-ee:/config/container/ntpd/network/docker0/> help option NAME option 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][2], 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:/# [^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. ### 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. [0]: networking.md [1]: https://github.com/kernelkit/infix/blob/main/src/confd/yang/infix-containers%402023-12-14.yang [2]: https://github.com/troglobit/mg [podman]: https://podman.io