virter

README

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 DRBD and LINSTOR.

Quick Start

First install and set up libvirt. Then download one of the releases. Virter is packaged as a single binary, 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

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 .

Installation Details

Virter requires:

• A running libvirt daemon on the host where it is run
• 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 prompted for a password.

Usage

For usage just run virter help.

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.

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 the 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.