embr

The purpose of this project was to explore running Ubuntu with Firecracker as a general purpose development machine. This is obviously not what Firecracker was developed for, but it was an opportunity to learn a little about it!

At present, embr can download and start Ubuntu cloud images using firecracker, with support for supplying a cloud-init file to customise the virtual machine. It relies upon dnsmasq to dynamically address the VM it creates.

I took a lot of influence from ubuntu-firecracker by @bkleiner, and this blog from @ahachete in the making of this project.

Using this approach, I was able to deploy the Canonical Observability Stack with Juju on MicroK8s inside a Firecracker VM:

Prerequisites

Before you can use or test this project, you'll need the following installed on your machine:

• dnsmasq
• firecracker
• jq
• yq

Quick start

You can start the project on a clean machine with ./embr launch.

This will do the following:

• Download and process the relevant Ubuntu cloud image (latest LTS by default)
• Create a network bridge device
• Start dnsmasq on that bridge
• Create two tap network interfaces for the VM (one for the metadata service, one for normal use)
• Create a folder structure for a VM, containing kernel, disk, initrd and a definition file
• Start firecracker and configure the VM over it's HTTP API
• Start the VM

With no arguments, embr will create a VM with 8 CPUs, 16GB RAM and a 20GB disk.

Once you've run ./embr launch, you'll get instructions on how to connect to your VM.

To cleanup your machine, run ./embr clean. Note that this will, kill started processes, remove any network interfaces and delete the VM.

Customising your machine

The embr launch command takes a number of arguments such that you can customise the CPUS, memory, disk and series that is used:

$ ./embr launch --help
embr is a tool for creating and launching Ubuntu virtual machines with Firecracker.

USAGE:
        embr launch [OPTIONS]

OPTIONS:
        -n, --name <name>
                Hostname of the virtual machine to create.
                Default: dev

        -c, --cpus <cpus>
                Number of virtual CPUs to assign to the VM
                Default: 8

        -m, --memory <mem>
                Amount of memory in GB to assign to the VM.
                Default: 16

        -d, --disk <disk>
                Size of disk for the VM in GB.
                Default: 20

        -f, --cloud-init <file>
                Filename of the cloud-init user data file to use for provisioning.
                Default: userdata.yaml

        -s, --series <series>
                The Ubuntu series codename to use. E.g. xenial, bionic, focal, jammy
                Default: jammy

        -h, --help
                Display this help message.

TODO

• Resume VM and make sure existing interfaces are present
• Multiple VM support
  • Store VMs in separate directories
  • Start / stop VMs independently
  • Status command to show running, IP, etc.
• Stop being a maniac and write this in Go

Done

• Better command line arg experience
• Output an accurate message with connection instructions on boot
• Figure out how to run DHCP on a tap interface
• Enable the use of standard Ubuntu cloud images
• Enable cloud-init support
• Add support for customising kernel and rootfs build