virter/virter

Virter

Virter is a command line tool for simple creation and cloning of virtual machines.

Virter supports VMs running standard general purpose distributions such as CentOS and Ubuntu. It is especially useful for development and testing of projects which cannot use containers due to kernel dependencies, such as https://github.com/LINBIT/drbd and https://github.com/LINBIT/linstor-server.

Quick Start

First install and set up https://libvirt.org/index.html. Then download one of the https://github.com/LINBIT/virter/releases. Virter is packaged as a single ***ary, so just put that into /usr/local/bin and you are ready to use Virter:

virter image pull centos-7 # also would be auto-pulled in next step
virter vm run --name centos-7-hello --id 100 --wait-ssh centos-7
virter vm ssh centos-7-hello
virter vm rm centos-7-hello

Depending on your host distribution and libvirt installation, you may need to:

• Set up a storage pool; and/or
• Configure AppArmor.

Usage

For usage just run virter help.

Some examples are provided in the examples directory. See the README files for the individual examples.

There is also additional documentation for the provisioning feature. This is useful for defining new images. These images can be used to start clusters of cloned VMs.

Installation Details

Virter requires:

• A running libvirt daemon on the host where it is run
• When container provisioning is used: A container runtime. Currently, Virter supports docker and podman.

Configuration is read by default from ~/.config/virter/virter.toml.

When starting Virter for the first time, a default configuration file will be generated, including documentation about the various flags.

Container runtime

Select the container runtime by setting container.provider to either docker or podman.

podman

Virter communicates with podman via it's REST-API. Make sure the API socket is available.

This may be done by:

• Starting podman via systemd: systemctl --user start podman.socket (use systemctl --user enable --now podman.socket to make this permanent)
• Start podman manually: podman system service

Network domain

If you require DNS resolution from your VMs to return correct FQDNs, add the domain to your libvirt network definition:

<network>
  ...
  <domain name='test'/>
  ...
</network>

By default, Virter uses the libvirt network named default.

DHCP Leases

Libvirt produces some weird behavior when MAC or IP addresses are reused while there is still an active DHCP lease for them. This can result in a new VM getting assigned a random IP instead of the IP corresponding to its ID.

To work around this, Virter tries to execute the dhcp_release utility in order to release the DHCP lease from libvirt's DHCP server when a VM is removed. This utility has to be run by the root user, so Virter executes it using sudo.

If execution fails (for example because the utility is not installed or the sudo rules are not set up correctly), the error is ignored by Virter.

So, to make Virter work more reliably, especially when you are running lots of VMs in a short amount of time, you should install the dhcp_release utility (usually packaged as dnsmasq-utils). Additionally, you should make sure that your user can run dhcp_release as root, for example by using a sudo rule like this:

%libvirt ALL=(ALL) NOPASSWD: /usr/bin/dhcp_release

This allows all users in the group libvirt to run the dhcp_release utility without being pro***ed for a password.

Console logs

The --console argument to virter vm run causes serial output from the VM to be saved to a file. This file is created with the current user as the owner. However, it is written to by libvirt, so it needs to located on a filesystem to which libvirt can write. NFS mounts generally cannot be used due to root_squash.

In addition, when the VM generates a lot of output, this can trigger virtlogd to roll the log file over, which creates a file owned by root (assuming virtlogd is running as root). To prevent this, increase max_size in /etc/libvirt/virtlogd.conf.

libvirt storage pool

Virter requires a libvirt storage pool for its images and VM volumes. By default, it expects a pool named default. Some libvirt distributions configure this pool automatically. Some, such as the standard packages on Ubuntu Focal, do not. If the pool does not exist, create it like this:

virsh pool-define-as --name default --type dir --target /var/lib/libvirt/images
virsh pool-autostart default
virsh pool-start default

AppArmor

On some distributions, AppArmor denies access to /var/lib/libvirt/images by default. This leads to messages in dmesg along the lines of:

[ 4274.237593] audit: type=1400 audit(1598348576.161:102): apparmor="DENIED" operation="open" profile="libvirt-d84ef9d7-a7ad-4388-bd5d-cfc3a3db28a6" name="/var/lib/libvirt/images/centos-8" pid=14918 comm="qemu-system-x86" requested_mask="r" denied_mask="r" fsuid=64055 ouid=64055

This can be circumvented by overriding the AppArmor abstraction for that directory:

echo '/var/lib/libvirt/images/* rwk,' >> /etc/apparmor.d/local/abstractions/libvirt-qemu
systemctl restart apparmor.service
systemctl restart libvirtd.service

Architecture

Virter connects to the libvirt daemon for all the heavy lifting. It supplies bootstrap configuration to the VMs using cloud-init volumes, so that the hostname is set and SSH access is possible.

Building from source

If you want to test the latest unstable version of Virter, you can build the git version from sources:

git clone https://github.com/LINBIT/virter
cd virter
go build .

Comparison to other tools

virsh

Virter is good for starting and cloning cloud-init based VMs. virsh is useful for more detailed libvirt management. They work well together.

virt-install

virt-install is built for images that use conventional installers. Virter uses cloud-init, making it simpler to use and quicker to start a fresh VM.

Running VMs in AWS/GCP/OpenNebula

Virter is local to a single host making snapshot/restore/clone operations very efficient. Virter could be thought of as cloud provisioning for your local machine.

Vagrant

Virter and Vagrant have essentially the same goal. Virter is more tightly integrated with the Linux virtualization stack, resulting in better snapshot/restore/clone support.

Multipass

Virter and Multipass have similar goals, but Multipass is Ubuntu specific.

Docker

Virter is like Docker for VMs. The user experience of the tools is generally similar. Docker containers share the host kernel, whereas Virter starts VMs with their own kernel.

Kata Containers

Virter starts VMs running a variety of Linux distributions, whereas Kata Containers uses a specific guest that then runs containers.

Weave Ignite

Ignite has very strong requirements on the guest, so it cannot be used for running standard distributions.

Development

Virter is a standard go project using modules. Go 1.13+ is supported.