I have a problem with the installation of the Vyos software inside an LXC container. The
As of last week LXC and LXD v3.0.0 were released.
Although there are many great new features/capabilities, to stay on topic, also released was lxd-p2c which is a tool to allow you to create a local (or remote) LXD container from either a physical machine or a VM.
So you can try now to install the ISO as say a KVM VM. After installed then create an LXD container using the lxd-p2c tool.
There is a video from FOSDEM 2018 by Stephane Graber demonstrating taking a CentOS VM running Apache and creating a working LXD CentOS container with the Apache running using lxd-p2c:
The LXD 3.0.0 release announcement is found here:
You don't. LXC containers are not true VMs, and are designed to operate from prebuilt disk images, not ISOs.
You'd need a VM to properly boot ISOs for installing the OS. That is achieved by something like VirtualBox, not by LXC/LXD containerization.