Vagrant deploys VMs (and containers) and vagrant-libvirt is a provider for Vagrant which allows Vagrant to create libvirt VMs.

vagrant-libvirt is a pain to install. I tried in RockyLinux and gave up. Seems like if your distribution is not supported is better to not try.

Conventions and Terminology

Box: package format for Vagrant environments. Find boxes
Provider: VirtualBox, Hyper-V, Docker or vagrant-libvirt the services that Vagrant uses to set up and create virtual environments.
Provisioners: Puppet, Chef or Ansible tools that allow users to customize the configuration of virtual environments.
Share: Remote access to the environment over HTTP, SSH or vagrant connect.

Install Vagrant in Debian

# curl -fsSL https://apt.releases.hashicorp.com/gpg | apt-key add -
# apt-add-repository "deb [arch=amd64] https://apt.releases.hashicorp.com $(lsb_release -cs) main"
# apt-get update
# apt-get install -y vagrant vagrant-libvirt
$ vagrant plugin install vagrant-libvirt
# systemctl enable --now libvirtd
# usermod -a -G libvirt $user

The plugin instalation has to be run as user.

Useful commands

vagrant up Starts the VM. The first time also creates and provisions the VM.
vagrant up --provision Start and provision the VM when it is stopped.
vagrant halt Stop the VM.
vagrant destroy Delete the VM.
vagrant reload Like halt followed by up
vagrant reload --provision Reloads the VM and provisions again.
vagrant ssh-config Generate the necessary configuration for ssh to connect. Append to ~/.ssh/config
vagrant ssh Connect over ssh to the VM.
vagrant provision Run provisioning in the VM.

To save the ssh config vagrant ssh-config >> ~/.ssh/config

When you update the playbook run vagrant provision or vagrant up --provision if the VM is stopped.

When you update the Vagrantfile run vagrant reload. Some options like the hostname is required to recreate the VM with vagrant destroy and vagrant up.

Create a Vagrant file

Basic Vagrant file.

Vagrant.configure("2") do |config|
  config.vm.box = "rockylinux/8"
  config.vm.provider "libvirt" do |v|
    v.title = "RockyLinux"
  end
end

Custom settings for the VM. More info

Vagrant.configure("2") do |config|
  config.vm.box = "rockylinux/8"
  config.vm.provider "libvirt" do |v|
    v.title = "RockyLinux"
    v.memory = 1024
    v.cpus = 2
    v.nic_model_type = "virtio"
    v.machine_virtual_size = 10
  end
end

Add Ansible to the mix

Install Ansible

# echo "deb http://ppa.launchpad.net/ansible/ansible/ubuntu focal main" | tee -a /etc/apt/sources.list.d/ansible.list
# apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 93C4A3FD7BB9C367
# apt update
# apt install -y ansible

More advanced Vagrant file with an Ansible playbook.

Vagrant.configure("2") do |config|
  config.vm.define :testvm do |testvm|
    testvm.vm.box = "rockylinux/8"
    testvm.vm.hostname = "rockylinux"
    testvm.vm.provider "libvirt" do |v|
      v.title = "RockyLinux"
      v.memory = 1024
      v.cpus = 4
      v.nic_model_type = "virtio"
      v.machine_virtual_size = 10
      v.storage_pool_name = "vms"
    end
    testvm.vm.provision :ansible do |ansible|
      ansible.playbook = "ansible_playbook.yml"
    end
    testvm.vm.synced_folder ".", "/mnt",
      type: "nfs",
      linux__nfs_options: ['rw','no_subtree_check','all_squash','async']
  end
end

Conclusion

Unless you need to deploy many VMs, it is not so useful. How many times do you deploy a VM? A container maybe, but a VM only once. Maybe a few times if you mess up.

Default credentials root/vagrant
vagrant-libvirt is not officially supported and it shows. If it works it is awesome.
vagrant-libvirt can control a local or a remote instance of libvirt.
Creating images is easy, but you need to configure them internally like password-less sudo, ssh key, possible dependencies (like rsync), etc. There are online guides on how to create images.
You have to allow DHCP and forwarding in the firewall.
Provisioning only happens when you create the VM by default.

It is awesome, but not for me.