Make new KVM VMs in less than 10 seconds

In the course of my day, I tend to spin up lots of VMs on my laptop. KVM is my hypervisor of choice, and since it supports libvirt, there are lots of great tools to make this easier. virt-manager is a nice GUI that’s very helpful for beginners. virt-install is my CLI tool of choice. But if you want to use dnsmasq for guest name resolution, and dhcp against libvirt networking, it can be a little tedious to type out everything over and over. So I decided to make a tool to save me some time and typing: kvminstall.

Hat tip to Rich Lucente who shared with me a bash script that inspired me to write kvminstall.

Installation

To install, use Python PIP. If you haven’t used this before, it’s easy to install with yum.

# yum install python-pip
# pip install kvminstall
# kvminstall --help
usage: kvminstall [-h] [-c CLONE] [-i IMAGE] [-v VCPUS] [-r RAM] [-d DISK]
                  [-D DOMAIN] [-N NETWORK] [--type TYPE] [--variant VARIANT]
                  [-f CONFIGFILE] [--verbose]
                  name

positional arguments:
  name                  name of the new virtual machine

optional arguments:
  -h, --help            show this help message and exit
  -c CLONE, --clone CLONE
                        name of the source logical volume to be cloned
  -i IMAGE, --image IMAGE
                        image file to duplicate
  -v VCPUS, --vcpus VCPUS
                        number of virtual CPUs
  -r RAM, --ram RAM     amount of RAM in MB
  -d DISK, --disk DISK  disk size in GB
  -D DOMAIN, --domain DOMAIN
                        domainname for dhcp / dnsmasq
  -N NETWORK, --network NETWORK
                        libvirt network
  --type TYPE           os type, i.e., linux
  --variant VARIANT     os variant, i.e., rhel7
  -f CONFIGFILE, --configfile CONFIGFILE
                        specify an alternate config file,
                        default=~/.config/kvminstall/config.yaml
  --verbose             verbose output

Configuration

In your .config directory, kvminstall sets up a yaml file with defaults. You can specify any of these interactively, or if you want to minimize typing, you can set these defaults in ~/.config/kvminstall/config:

---
vcpus: 1
ram: 1024
disk: 10
domain: example.com
network: default
mac: 5c:e0:c5:c4:26
type: linux
variant: rhel7

The MAC address can be specified as up to 5 :-delimited fields. If you want to specify fewer, kvminstall will auto-complete with random, available values.

Usage

The current version 0.1.3 supports only image-based installs — either by snapshotting an LVM volume, or by copying an image file. I intend to add kickstart and iso support, but hey, release early, release often.

Image File

Most people will probably want to copy an image file. Let’s assume that you’ve built a base image, and its root volume lives in /var/lib/libvirt/images/rhel71base.img. (Next post will be on building base images.) To create a new VM, based on that image, called ‘testvm’:

# kvminstall -c /var/lib/libvirt/images/rhel71base.img testvm

You’re mostly I/O bound here, as your copying rhel71base.img -> testvm.img. Shortly after that’s finished, you’ve got a new VM with all of your host and guest networking configured.

# virsh list
 Id    Name                           State
----------------------------------------------------
 2     testvm                         running

# grep testvm /etc/hosts
192.168.122.27	testvm.example.com testvm
# ssh testvm
Last login: Thu Aug 27 13:30:25 2015 from 192.168.122.1
[root@testvm ~]# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 5c:e0:c5:c4:26:7a brd ff:ff:ff:ff:ff:ff
    inet 192.168.122.27/24 brd 192.168.122.255 scope global dynamic eth0
       valid_lft 2141sec preferred_lft 2141sec
    inet6 fe80::5ee0:c5ff:fec4:267a/64 scope link 
       valid_lft forever preferred_lft forever
# nslookup testvm.example.com
Server:		192.168.122.1
Address:	192.168.122.1#53

Name:	testvm.example.com
Address: 192.168.122.27

The guest networking has been setup with virsh. An available IP and MAC address has been automatically picked based on your DHCP scope. (In the next version I’ll add support for specifying an IP address.)

# virsh net-dumpxml default
<network connections='1'>
  <name>default</name>
  <uuid>431ea266-8584-4e10-866a-fc1a3ad419b5</uuid>
  <forward mode='nat'>
    <nat>
      <port start='1024' end='65535'/>
    </nat>
  </forward>
  <bridge name='virbr0' stp='on' delay='0'/>
  <mac address='52:54:00:d0:5e:a3'/>
  <dns>
    <host ip='192.168.122.27'>
      <hostname>testvm.example.com</hostname>
    </host>
  </dns>
  <ip address='192.168.122.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.122.2' end='192.168.122.254'/>
      <host mac='5c:e0:c5:c4:26:7a' name='testvm.example.com' ip='192.168.122.27'/>
    </dhcp>
  </ip>
</network>

The dnsmasq service will be automatically restarted after /etc/hosts is updated. This way, so long as your resolv.conf is set up properly in your base image, DNS hostname resolution will work in your guest network.

LVM Volume

Now I use LVM volumes on my laptop, served up from an M2.SATA drive. This gives me better I/O since I’ve split out host and guest storage devices. It’s also much faster to snapshot a base image’s root volume. Using kvminstall with an LVM snapshot, you can get VM creation time down to seconds. My LVM volume group is called libvirt_lvm.

# lvs
  LV                 VG          Attr       LSize   Pool Origin     Data%  Meta%  Move Log Cpy%Sync Convert
  home               fedora      -wi-ao---- 500.00g                                                        
  root               fedora      -wi-ao---- 366.82g                                                        
  swap               fedora      -wi-ao----  64.00g                                                        
  rhel71base         libvirt_lvm owi-a-s---  10.00g                                                        
# time kvminstall -c /dev/libvirt_lvm/rhel71base testvm

real	0m2.217s
user	0m1.012s
sys	0m0.218s
[root@w550 ~]# ssh testvm
Warning: Permanently added the ECDSA host key for IP address '192.168.133.164' to the list of known hosts.
Last login: Sat Aug  8 21:02:29 2015 from 192.168.133.1
[root@testvm ~]# exit
# lvs
  LV                 VG          Attr       LSize   Pool Origin     Data%  Meta%  Move Log Cpy%Sync Convert
  home               fedora      -wi-ao---- 500.00g                                                        
  root               fedora      -wi-ao---- 366.82g                                                        
  swap               fedora      -wi-ao----  64.00g                                                               
  rhel71base         libvirt_lvm owi-a-s---  10.00g                                                        
  testvm             libvirt_lvm swi-aos---  10.00g      rhel71base 0.06                                   

Upcoming features

It would be nice if we could — just as quickly — remove the VMs, or even reset them back to their base images. In the next version, expect kvmuninstall and kvmreset commands.

I’d love feedback. Please feel free to comment here or open issues on the GitHub project page.

Stay tuned for my next article on building base images for easy cloning.

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