CoreOS

CoreOS #

CoreOS is deprecated. I’ve played with its successor Fedora CoreOS but I’m not sure how easily these tips translate to it.

QEMU Guest Agent #

When CoreOS is running in a virtual machine, the guest agent qemu-ga is required for the host to discover the machine’s network setup, specifically it’s IP. You can start the guest agent in an Alpine container:

docker run -d \
  -v /dev:/dev \
  --privileged \
  --net host \
  alpine ash -c 'apk add qemu-guest-agent && exec qemu-ga -v'

An alternative for very minimal machines deployed with virt-install exists, where the necessary channel needs to be created in the domain XML first.

Add the following device by editing the domain definiton with virsh edit $name:

<channel type='unix'>
  <target type='virtio' name='org.qemu.guest_agent.0'/>
</channel>

You’ll need to fully shut the machine down and start it again. A single reboot is not enough. Now download a qemu-guest-agent package in a TAR archive.

Extract the contained qemu-ga binary to /opt/bin and use the following systemd service:

[Unit]
Description=QEMU Guest Agent
ConditionPathExists=/dev/virtio-ports/org.qemu.guest_agent.0

[Service]
ExecStart=/opt/bin/qemu-ga

[Install]
WantedBy=multi-user.target

fcos Installer #

I wrote a little script to create new Fedora CoreOS based virtual machines while playing around with it. I’m pubishing it here before cleaning up some unused files:

#!/usr/bin/env bash

# helpers
err() { echo "err: $1" >&2; }
required() { if [[ -z $1 ]]; then err "$2 required"; exit 1; fi; }
usage() { cat <<USAGE
usage: $ fcos-install [-args] [extra]
  -n name     : machine name
  -c cpus     : number of vcpu cores
  -m memory   : memory in MiB
  -N netname  : use network name
  -d disk     : size of disk in GiB
  -D          : download latest iso
USAGE
}

# default config
VCPUS="2"
MEMORY="2048"
NETWORK="vf-eno4"
DISKSIZE="24"
DOWNLOAD="false"

# commandline parser
while getopts ":n:c:m:N:d:Dh" OPTION; do
  case "$OPTION" in
    # invalid cases
   \?) err "invalid option: $OPTARG"; exit 1;;
    :) err "invalid option: $OPTARG requires an argument"; exit 1;;
    h) usage; exit 0;;
    # arguments
    n) MACHINE="$OPTARG";;
    c) VCPUS="$OPTARG";;
    m) MEMORY="$OPTARG";;
    N) NETWORK="$OPTARG";;
    d) DISKSIZE="$OPTARG";;
    D) DOWNLOAD="true";;
  esac
done
shift "$((OPTIND-1))"

# check required values
required "$MACHINE" "machine name"
required "$VCPUS" "number of cpu cores"
required "$MEMORY" "amount of memory"
required "$NETWORK" "network name"
required "$DISKSIZE" "disk size"

# download and use latest available iso
if [[ $DOWNLOAD = true ]]; then
  podman run --privileged --pull=always --rm \
    -v /var/lib/libvirt/boot:/data -w /data \
    quay.io/coreos/coreos-installer:release -- download -f iso
fi
ISO=$(ls /var/lib/libvirt/boot/fedora-coreos-*-live.x86_64.iso | sort -rV | head -1)

# run virt-install
virt-install --name="$MACHINE" --os-variant="fedora31" \
  --vcpus="$VCPUS" --memory="$MEMORY" --memorybacking="hugepages=on" \
  --network="network=$NETWORK" --graphics="none" --disk="size=$DISKSIZE" \
  --location="$ISO,kernel=/images/pxeboot/vmlinuz,initrd=/images/pxeboot/initrd.img" \
  --extra-args="initrd=/images/pxeboot/initrd.img,/images/ignition.img mitigations=auto,nosmt systemd.unified_cgroup_hierarchy=0 coreos.liveiso=$(basename "${ISO%%-live.x86_64.iso}") ignition.firstboot ignition.platform.id=qemu console=tty0 console=ttyS0,115200n8"