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