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.
Jason Callaway 