2.4. KVM Setup Instructions

2.4.1. Overview

This document will help define one possible method to setup a KVM hypervisor host as a Digital Rebar endpoint, running KVM, and provisioning Virtual Machines on that KVM host.

The configuration of this setup utilizes the RackN kvm-test plugin which is currently in Alpha or Experimental stages. It has limited functionality, but does provide useful capabilities for managing the KVM environment, and appears to be relatively stable.

This environment is tested and running as a primary development platform for one of the RackN engineers

Please feel free to provide any feedback or alternative setup methods.

2.4.2. Architecture

The setup of the RackN kvm-test Plugin Provider requires that the DRP Endpoint service (dr-provision) run directly on the same machine that the KVM hypervisor services are also running on. Please see the Future ToDos at the bottom of this document regarding this.

The setup of this environment utilizes the DRP Endpoint running on the bare hardware machine, alongside the KVM services. All Virtual Machines will be connected to a single bridge (called kvm-test in this document), which provides the connectivity to the Hypervisor and outbound external network connectivity for the Virtual Machines.

The Hypervisor will provide NAT/Masquerading services and act as the Default Gateway to the External network (either your local network, or outbound to the Internet).

Here is a simplified diagram:

|   External   |
|              +------------ ( Internet )
|    Switch    |
|     eth0     | (ex:
|              |
| DRP  Machine |   * must be a physical server
|   KVM Qemu   |   * performs IP gateway NAT/Masquerading
|              |
|   kvm-test   | (ex:
        |                     KVM Bridge (kvm-test -
        +-----------------------------------+------------------------------------+------- ...
        |                                   |                                    |
+-----------+                          +----+------+                          +--+--+
|   eth0    | (ex:     |   eth0    | (ex:     |     |
|           |                          |           |                          |     |
|   VM 01   |                          |   VM 02   |                          | ... |
|           |                          |           |                          |     |
+-----------+                          +-----------+                          +-----+

This method has a few advantages:

  • You can have many target VMs and they are easy to create/destroy
  • The DRP Endpoint controls the KVM network bridge setup/tear down
  • The DRP endpoint may have Internet access, and can selectively provide Internet access to the target VMs using standard Linux tools
  • Virtual Machine creation/destruction can be performed from Digital Rebar APIs / Control
  • Virtual Machine power operations can be performed form Digital Rebar APIs / Control
  • KVM can replicate many different machine architectures and configurations, Legacy BIOS, UEFI BIOS, etc.
  • The primary limitaiton to number of VMs is physical memory, disk space, and your oversubscription comfort levels

2.4.3. Prerequisites

This test environment is based on CentOS 7.8 and Libvirt 5.0.0 and QEMU-KVM 2.12.0. It is entirely likely that this setup will run fine under other Linux Distros. You may need to adjust package selections or other distro specific isms to the below recipe.

You will need:

The remainder of this document assumes you have CentOS 7.8 installed on your physical server, and you are accessing the system either from the console, or an SSH session.

2.4.4. Install KVM/Libvirt

Create a CentOS yum repository with the latest Qemu/KVM and Libvirt packages:

cat << EOF-REPO > /etc/yum.repos.d/CentOS-Virt.repo

# CentOS-Virt

name=CentOS-$releasever - Virt Libvirt Latest

name=CentOS-$releasever - Virt KVM Common


Install the packages:

yum makecache
yum install qemu-kvm libvirt libvirt-python libguestfs-tools bridge-utils iptables iptables-services util-linux unbound curl wget jq

2.4.5. Install Digital Rebar

Install Digital Rebar based on the Quick Start Guide or Production Install documentation, *WITH THE FOLLOWING DIFFERENCE*

  • use “production” mode (do not use --isolated install flag)
  • add --systemd to enable the SystemD startup unit files

Example installation command line:

  • curl -s get.rebar.digital/stable | bash -s -- install --systemd

Once you have a basic DRP Endpoint up and running, add the kvm-test Plugin Provider via the Catalog in the UX, or via the following command line usage:

  • drpcli catalog item install kvm-test

2.4.6. Install EFI Firmware Code for Virtual Machines

The default configuration and machine creating by the Digital Rebar plugin will build VMs with UEFI BIOS and firmware. This requires installation of the CODE and VARS to support the EFI mode in the VMs. There are many ways to integrate EFI in to KVM/Libvirt guests. This is only one, and is required to be setup this way for this environment.

wget https://s3-us-west-2.amazonaws.com/get.rebar.digital/artifacts/fw.tar.gz -O /tmp/fw.tar.gz
cd /
tar -xzvf /tmp/fw.tar.gz

If you are building guest VMs direclty with Libvirt/Qemu tools, you are free to use any other UEFI firmware packages or solutions. Additionally, you can create virtual machines with Standard / Legacy BIOS boot mode and not utilize UEFI at all.

2.4.7. Create the kvm-test Virtual Machine Subnet

Now create a DHCP Subnet (pool) for the Virtual Machines to utilize. If you have previously created a DHCP pool in DRP, you may need to either destroy that pool, or create this new pool for your VMs.

cat << EOF_SUBNET > $HOME/kvm-test-net.yaml
  "Name": "kvm-test",
  "ActiveEnd": "",
  "ActiveLeaseTime": 3600,
  "ActiveStart": "",
  "Enabled": true,
  "Meta": {},
  "NextServer": "",
  "OnlyReservations": false,
  "Options": [
    { "Code": 3,  "Description": "Default GW",  "Value": "" },
    { "Code": 6,  "Description": "DNS Servers", "Value": "" },
    { "Code": 15, "Description": "Domain",      "Value": "kvm-test.local" },
    { "Code": 1,  "Description": "Netmask",     "Value": "" },
    { "Code": 28, "Description": "Broadcast",   "Value": "" }
  "Pickers": [ "hint", "nextFree", "mostExpired" ],
  "Proxy": false,
  "ReservedLeaseTime": 7200,
  "Strategy": "MAC",
  "Subnet": "",
  "Unmanaged": false

drpcli subnets create $HOME/kvm-test-net.yaml


See the DNS notes section below for additional options related to name server lookup configurations.

Once our DHCP Subnet is created, we can now define the KVM Plugin configuration, which works cooperatively with the DHCP Subnet.

2.4.8. Instantiate the kvm-test Plugin and Configuration

The kvm-test Plugin Provider adds the ability to manage KVM networks. We have to instantiate a Plugin with the network details to create/enable the bridges for this setup. Create a YAML file with the following configuration to specify the storage pool, and the network (subnet) configurations:


Your network configuration here must match the Subnet created above.

cat << EOF-PLUGIN > $HOME/kvm-test-plugin.yaml
Name: kvm-test
Description: ""
Meta: {}
  kvm-test/storage-pool: dirpool
    domain: kvm-test.local
    name: kvm-test
Provider: kvm-test


# now create the plugin from the above config file
drpcli plugins create $HOME/kvm-test-plugin.yaml


This is only one possible configuration. You can specify different addressing, DNS servers, etc. to match your requirements. See the DNS topic below.

Once you create the Plugin, you should now be able to see the network bridge in the OS of your DRP Endpoint. If you do not, restart DRP (systemctl restart dr-provision), and check again:

# ip a sh kvm-test
7: kvm-test: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether fe:54:00:28:20:b7 brd ff:ff:ff:ff:ff:ff
    inet brd scope global kvm-test
      valid_lft forever preferred_lft forever

# brctl show kvm-test
bridge name bridge id               STP enabled     interfaces
kvm-test            8000.fe54002820b7       no              vnet0

2.4.9. Setup IP Forwarding and NAT Masquerading

This portion of the configuration sets up the DRP Endpoint machine as a router and IP NAT Masquerading host for the Virtual Machines that DRP will manage and control. This has the drawback that all VM network traffic will route through the DRP Endpoint Operating System, however, it is a simplified setup that works very well and is repeatable and independent from the machines external network topology.

Configuring the Virtual Machine networks differently (eg with multiple NICs), and creating associated Bridges to other network devices is entirely possible, but outside the scope of this document.

The vm-bridge.sh <https://gitlab.com/rackn/provision/blob/v4/tools/vm-bridge.sh> script uses Digital Rebar Provision Command Line Interface (CLI) to read DRP Endpoint subnet information and then enables extremely simplified iptables rules to perform these tasks. Other firewall services can be substituted, as long as you perform these similar capabilities. We encourage you to also increase the external network rulesets to better protect your system services.


If you utilize other firewall services (eg firewalld), ensure you perform
the equivalent setup as below.
curl -fsSL https://raw.githubusercontent.com/digitalrebar/provision/v4/tools/vm-bridge.sh -o install.sh | bash -s --

2.4.10. Virtual Machine Creation

The DRP based KVM plugin supports creating and provides limited control over virtual machine actions (poweron, poweroff, reboot, etc.). To support these actions, the Machine must have the KVM specific Parameters:

  • kvm-test/machine: { ... }
  • machine-plugin: kvm-test

These values help the plugin to control the Virtual Machine state correctly.


The create VM variations below all initially create the Virtual Machine as an object in DRP to manage, and the Virtual Machine within KVM; you will need to power the Machine(s) on after creation (details below). Create VMs via Portal (UX)

You can create new virtual machines from the RackN hosted Portal, by visiting the Plugins menu page, and then selecting the kvm-test plugin that was created earlier. On this page, there is a simple dialog input form to specify the Machine base name, and number of machines to create. These machines will be created based on the internally compiled in machine specs, which can not be changed easily at this time. Create VMs via Command Line (drpcli)

The drpcli command can be used to create a Machine object, and by setting specific Param values on the Machine object, the system will create VMs. The below shell script builds up the appropriate Machine Ojbect JSON information, initiates the create, and powers on the VM. You can just run the script to receive a randomized machine name, or pass a VM name as ARGv1 to the script.

cat << 'EOF_SCRIPT' > $HOME/create-vm.sh
#!/usr/bin/env bash
# create a DRP managed KVM Virtual Machine

# optionally specify machine name as ARGv1

MID=$(mktemp -u XXXXXX | tr '[:upper:]' '[:lower:]')

{ \"Name\": \"$NAME\",
  \"Params\": {
    \"machine-plugin\": \"kvm-test\",
    \"kvm-test/machine\": {
    \"arch\": \"x86_64\",
    \"bios\": \"bios\",
    \"bridge\": \"kvm-test\",
    \"cores\": 2,
    \"disk-size\": 20,
    \"memory\": 2048,
    \"Name\": \"$NAME\",
    \"pool\": \"default\",
    \"uuid\": \"$UUID\"

echo ">>> Creating Machine:  $NAME"
drpcli machines create "$JSON"

echo ">>> Powering on machine: $NAME"
drpcli machines action Name:$NAME poweron

exit 0

chmod +x $HOME/create-vm.sh

Example usage of the script, creating VM named vm-test-01:

  • $HOME/create-vm.sh vm-test-01 Create VMs via virsh or other Methods

You are welcome to create Virtual Machines through any other traditional VM creation mechanism that is supported by your setup. Just set the Virtual Machine to boot PXE first, and generally speaking, it should be discovered, and added in to inventory on the DRP Endpoint to be managed as any other normal machine.

This method allows you greater control over the virtual machine specifications if you need to test different hardware architectures, components, BIOS setups, etc.


Machines created this way can not be power controlled via DRP, unless you add Machine Params as specified above. Reference a Digital Rebar created VM for the correct structure of the Params. Power Control of your VMs

Power on, off, reboot, etc. controls are enabled through DRP Plugin actions. The actions work as long as the Machine object has the correct Params set on it to allow the Plugin system to reference properly.

If you are creating machines directly via virsh, qemu-kvm, qqemu-system-x86_64, or other options; you must manually add the Params to the DRP Machine object. In this case, it is recommend you create a VM via the Portal/UX, observe the Machines kvm-test/* param values, and replicate those.

For VMs created via the Portal/UX or CLI tool, you can use DRP to perform the machine actions. In the Portal, use the standard Actions dialogs on the Machines menu page, or on the Machines detail panel to effect power changes. For CLI actions, perform the following:

VM="MACHINE_NAME"  # change this!

# get a list of the Actions availble on the Machine
drpcli machines actions Name:$VM | jq -r '.[].Command'

# perform an action
drpcli machines action Name:$VM poweron


It appears that the CLI method of passing machine actions for VM power control are not very reliable. Utilize the Portal/UX method if you have issues with the CLI method.

2.4.11. Virtual Consoles for VMs

There are a couple of options for managing the view/interaction with the console of the VMs. These all basically come down to how the VM was created, and the supported console setup inside the Machine specifications. The default setup for VMs created by the Portal/UX Plugin operation, or the CLI tooling utilize a Spice display method. You can find more at the following resources:

The Virtual Machine display specifications can be changed to utilize VNC and VNC clients as well.

In all cases, if you are remote from the KVM hypervisor, you will need to either forward Ports to the KVM Hypervisor, setup a VPN connection to connect to the Hypervisor and your Guest VMs, or otherwise arrange to have the Spice/VNC ports opened up on the External network interface of your hypervisor for access directly over the network.

At the shell/command line of the Hypervisor, you can see the emulated serial console of the VM by use of the virsh tool, as follows:

virsh console <VM_NAME>

If there is no console output, it may appear that you are not connected - hit <Enter> to regenerate the Shell login dialog on the TTY in this case.

2.4.12. Extra Disks and NICs for your VMs

If you require additional storage devices (eg “disks”) inside your VM, more than the single defined NIC, or other hardware changes, you can create VMs from the Hypervisor tooling with these devices. Any configuration that allows DRP to have access on one Boot/Control NIC will work.

You will need to add any additional Hypervisor network (bridges, NAT/Masqurading, etc.) necessary to support additional NICs.

2.4.13. A Note about VM DNS Services

The above configuration has the DRP Subnet set external DNS servers for resolving name server lookups. This works well, but you can also set up services like Unbound in the DRP Endpoint / KVM hypervisor and limit the DNS queries based on Unbound rules and capabilities. A simple example that provides pass-through recursive DNS query and caching support for Unbound is as follows:

# assumes package 'unbound' was installed as per above examples

cat << EOF_UNOUND > /etc/unbound/conf.d/kvm-test.conf
# kvm-test DRP managed virtual machine network
  access-control: allow
  access-control: ::1 allow

systemctl restart unbound

Now you can adjust the Subnet specifiction for the DNS Option (Code 6) to set the DNS server that your DHCP clients use to:


You can find more information on configuration and management of the Unbound services at:

2.4.14. Additional ToDos and Enhancement Ideas

The kvm-test plugin doesn’t receive much love from RackN. It works pretty well in it’s limited use case today. The primary drawback is the Machine specifications are hard-wired in to the Plugin Provider golang compiled binary. This makes changing hardware types left to the direct Virtual Machine creation path within KVM/Qemu/Libvirt, and not via the DRP Plugin mechanism.

If you find the KVM Test plugin useful, and are so inclined, we welcome Pull Requests enhancements to add value and additional capabilities to the tooling. You can find the Github repo and code for kvm-test at:

Some places that could use love and enhancement:

  • More flexible Machine creation specifications
  • A workflow designed to run in the special Self Runner to configured the DRP Endpoint with KVM configuration
  • Remote API invocation of KVM hypervisors across the network, so DRP Endpoint isn’t required to be on the same KVM host

There are many more small areas that can be enhanced. Please contact RackN if you have any thoughts or questions to make this better!

2.4.15. Example Machine Creation - virt-install

A simple example of using virt-install to create a Virtual Machine:

virt-install \
  --name=winders --ram=4096 --cpu host --hvm --vcpus=2 \
  --os-type=windows --os-variant=win10 \
  --disk /var/lib/libvirt/images/winders.qcow2,size=80,bus=virtio \
  --pxe --network bridge=kvm-test,model=virtio \
  --graphics vnc,listen=,password=foobar --check all=off &

This creates the Virtual machine and specifies PXE network boot. The machine should create and load the Sledgehammer Discovery image. Note that when the Machine object is created in Digital Rebar, the name will not match - it will recieve the dname based on the PXE boot NIC MAC address like d52-54-00-3b-c5-76.

The console is availble via the VNC protocol on localhost with the password foobar in this example.