This is a framework to build debian (ubuntu) LXC containers from scratch.
- Guest containers - in place of linux VMs or entire systems
- Host container - read more on the containervisor (cvisor) below
- Installers - use a live installer to quickly bootstrap a system by copying an existing system
While LXC is used to build the live system, it is not necessary in order to run it. The output is a fully functioning system.
The rootfs of the container can be exported and embedded as follows:
- The system is squashed and compressed using squashfs with gzip.
- The squashfs image is embedded into an initramfs
- The initramfs uses debian live-boot with a small patch to load the squashfs image, and mount an overlay on top of it
- A fully functioning read-write system with optional persistence can then be booted
As only a kernel and the initramfs are required, this is extremely portable:
- syslinux / isolinux may be used to easily create a livecd / iso / USB
- A simple PXE config can be used for network booting
The following kernel arguments are required in order to successfully boot:
boot=live root=/dev/ram0 live-media=initramfs
- boot=live - this triggers the necessary live-boot initramfs scripts
- root=/dev/ram0 - this tricks the kernel into using it's own initramfs as the root filesystem, so it won't panic
- live-media=initramfs - this tells live-boot to look at it's own initramfs to find the embedded squashfs image
So long as a bootloader can supply the above kernel arguments, and can load the kernel and initramfs, the cvisor can be booted.
Optionally, a container can be transformed into a 'container-supervisor' or 'cvisor', running directly on the host.
The cvisor image contains lxd to manage lxc images.
This provides a shim to run other LXC containers, potentially performing more complex or specialized tasks.
Thus, a generic host can take on other more specialized roles with relative ease - with no need to reboot, re-image, or reinstall.
More on this later (lxd work in progress)
Building containers is quite simple with few requirements:
- A linux system with a modern kernel
- lxc, squashfs-tools
- optional (cdrom / iso support): syslinux, mkisofs
A named config file describes a few variables that tells the framework how to build.
To build cvisor:
./build.sh -n cvisor
This will result in a squashfs image, and a kernel/initramfs pair suitable for booting
You can optionally run any of the build steps with the -i flag. To package the system up into an ISO:
./build -n cvisor -i iso
For additional help:
./build -h