KVM

KVM network refer docby Snail

Introduction of configure virtual network and KVM based on libvirt.

Introduction

This is a reference document of building KVMs with certain networks to support BMC deployment virtualization.

It requires the basic knowledge of Linux bridge, net-configure interface, qemu-kvm and libvirt.

Network physical diagram

KVM Install

OS: This document is based on Red Hat Enterprise Linux 6.5
Hardware:
CPU supports Virtualization Technology
Memory more than 4G
Harddisk more than 10G
User: The user to do below steps should be root or gets sudo authority.

Install dependencies and tools

To make a check your machine supports KVM, use grep as below

grep -E '(vmx|svm)' /proc/cpuinfo
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb rdtscp lm constant_tsc rep_good unfair_spinlock pni pclmulqdq vmx ssse3 cx16 pcid sse4_1 sse4_2 x2apic popcnt aes hypervisor lahf_lm vnmi ept
<!-- more information is ignored -->

If the output is not empty, use yum to install dependencies and tools as below

yum install qemu-kvm qemu-kvm-tools libguestfs-tools -y
yum groupinstall Virtualization-Platform Virtualization-Clients Virtualization-Tools -y

To verify the installation, execute

/usr/libexec/qemu-kvm --version

Host network configuration

NetworkManager: The NetworkManager service must be stopped or it’ll interferes the condition of networks. Execute service NetworkManager status and if get message as “NetworkManager (pid $pid_numb) is running…” then execute service NetworkManager stop
Iptables: If your new network can’t access the Internet, check the rules of your iptables or shut down your iptables by executing service iptables stop

The Configuration of no bonding

Setting up a linux bridge

Go into network configuration directory.
cd /etc/sysconfig/network-scripts
Create a configure file named as ifcfg-br*, * must be a number. Here use ifcfg-br1 as an example.
Example 1:

#This is used when there's a DHCP server.
DEVICE=br1
ONBOOT=yes
BOOTPROTO=dhcp
TYPE=Bridge
STP=on

Example 2:

#This is used when there's no DHCP server.
DEVICE=br1
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.100.16
NETMASK=255.255.255.0
TYPE=Bridge
STP=on

Configurate the eth

Here assume that eth1 is linked to the br1 above.
Create a configure file named as ifcfg-eth1.

DEVICE=eth1
TYPE=Ethernet
BRIDGE=br1
ONBOOT=yes
BOOTPROTO=none

Validate the linux bridge

To now, the linux bridge is completely setted but not in validation. To validate it, execute service network restart.
Ensure that the NetworkManager is closed before doing this.
If any errors occurs, do rm /etc/udev/rules.d/70-persistent-net.rules and try again.
If no errors occur, execute brctl show to get the information as follow:

bridge name    bridge id            STP enabled     interfaces  
br1            8000.525400117fda    yes             eth1

Using libvirt tools to build virtual networks

Definition of virtual network

Libvirt use xml format file to define a network. For more
This example showes a bridge forward network. The libvirt will create a tap device and bond it to a bridge. Then the guest virtual machine will use this tap as its ethernet device.

<network>
    <name>virnet-1</name>
    <forward mode="bridge"/>
    <bridge name="br1"/>
</network>

name: The network name for libvirt. You can use virsh net-list --all to list all and virsh net-info $netname to get more information.
bridge: The name of the to be bonded bridge. After the net is started by libvirt, you can check it: ifconfig $netname.
forward: The forward mode of the virtual network. To use linux bridge, the mode should be “bridge”.
bridge: When forward mode is setted as bridge, use this to assign the linux bridge to virtual network. The name is the device name in ifcfg-br?.

Active the virtual network

virsh net-create $xml_file then a temporaty virtual network is created. If you this net to be automatically started at boot, then virsh net-autostart $netname.

The Configuration including bonds

Most of the steps are the same with no bonding one. The difference is as follow steps.

Setting up a linux bridge

Please refer to the part of setting up a lunix bridge in “no bonding”. They are exactly the same as those steps.

Setting up a bonding

Go into network configuration directory.
cd /etc/sysconfig/network-scripts
Create a configure file named as ifcfg-bond*, * must be a number. Here use ifcfg-bond2 as an example.

DEVICE=bond2
TPYE=Bonding
BRIDGE=br2
BONDING_OPTS="mode=1 miimon=200"
ONBOOT=yes
BOOTPROTO=none
USERCTL=no

Above assumes that this bond2 will link to a linux bridge named br2.
The BONDING_OPTS give the detailed options of bonding. Here the “mode 1” means that one is active while others ara backup and the “miimon=200” means the MII will verify if a NIC is active every 200 milliseconds. To know more, go to Redhat site.
The USERCTL=no means user except root can not configure this net device.

Configurate the eth

Here assume that eth2 and eth3 is bonded to the bond2 above.
Create a configure file named as ifcfg-eth2 first.

DEVICE=eth2
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=none
MASTER=bond2
SLAVE=yes

Then a ifcfg-eth3.

DEVICE=eth3
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=none
MASTER=bond2
SLAVE=yes

Others

The rest steps like manage linux bridges and virtual networks are the same as “The Configuration of no bonding”.

Create a KVM

Create a KVM using an existing image

Assume that there’s an image named “bmc15b-Fri.qcow2” which is created from some other KVM’s snapshot.

virt-install \
    -n BMC-release \
    -r 512 \
    --vcpus 1 \
    --network network=virnet-1 \
    --graphics vnc \
    --hvm \
    --virt-type kvm \
    --os-type linux --os-variant rhel6 \
    --disk path=/var/tmp/bmc15b-Fri.qcow2,format=qcow2 \
    --cdrom /var/tmp/seed.iso \
    --boot hd

Then a virtual machine named BMC-release which get 512MB ram, one virtual CPU and virnet-1 as its eth0 is created.

–network network=vnet-1: When you create a virtual machine, this option means VM will use a tap device named vnet-1 as its default net device link to the br1.
–cdrom /var/tmp/seed.iso: File or device use as a virtual CD-ROM device for fully virtualized guests.
–boot hd: A boot defines where the VM will boot from. Here it boots from hd(hard disk).

Auto install a OS base image as raw format

Assume that there’s a official rhel iso named rhel-server-6.5-x86_64-dvd.iso, you can use a premade ks.cfg file to do auto-install.

virt-install \
    -n BMC-release \
    -r 1024 \
    --vcpus 1 \
    --network network=virnet-1 \
    --graphics vnc \
    --hvm \
    --virt-type kvm \
    --os-type linux --os-variant rhel6 \
    --disk path=/var/tmp/bmc15b-Fri.img,size=20G 
    --location ${ISO_PATH}/rhel-server-6.5-x86_64-dvd.iso  \
    --initrd-inject=ks.cfg  \
    --extra-args "ks=file:/ks.cfg"

You can view the installation process in vnc viewer.

Edit image using guestfish

Sometimes a image may need to be made some changes before release. The guestfish is a tool to help doing this safely.
Assume that here gets a RHEL qcow2 image called rhel6.5_demo.img. Mount the image in read-write mode as root, as follows:

# guestfish --rw -a centos63_desktop.img

Welcome to guestfish, the libguestfs filesystem interactive shell for
editing virtual machine filesystems.

Type: 'help' for help on commands
    'man' to read the manual
    'quit' to quit the shell

><fs>

Then use run command to launch a lightweight virtual machine.

><fs> run

If viewing the file systems in the image is requited, using the list-filesystems command.

><fs> list-filesystems
/dev/vda1: ext4

Mount the disk or volumn and start to edit files.

><fs> mount /dev/vda1 /
><fs> rm /etc/udev/rules.d/70-persistent-net.rules
><fs> edit /etc/sysconfig/network-scripts/ifcfg-eth0

When everything is done, use exit to leave.
> exit

Reference

Published 12 October 2014

KVM

libvirt