Welcome to Pandora's Box(Why)

Keep It Simple, Stupid!

Fork me on GitHub

Playing With Xen Under Centos6.4 to Build Your Own VPS

| Comments

Believe it or not, we are under an age called Cloud Computing.

I used to be curious about VPS(Virtual Private Server), how they work, how to build them, etc. As far as I know, AWS, GCE or whatever else solutions depend heavily on Virtualization Technologies and AWS is definitly playing with Xen currently.

I would like very much to have a trial for building my own VPS and blow are my steps doing it. You may need to read some basic wikis about Xen, Xen Overview and Xen Beginners Guide should do some help:–)

Getting a working Dom0 on Centos6.4

Install Centos

Use whatever way you like, remember a minimal install is recommended.

Install Xen

Thanks to Xen4Centos Project, we can get Xen installed in several simple commands(log in as root).

yum -y update
yum install centos-release-xen
yum install xen
/usr/bin/grub-bootxen.sh
reboot

After your machine comes to alive, simply type:

uname -r
xl list

to verify that Xen Dom0 is running.

Config network

I use DHCP to get a valid IP for my box and there is a trick if you can’t ping each other when two machinea are in the same LAN(probably the routing table is not working for you and just delete the record from your routing table).

As me, for example, my laptop got a IP, say 192.168.0.10 and my VPS got 192.168.0.11, but they can’t talk to each:–(

First, check your routing table,

route

Then, delete the record that is evil,

route del -net 192.168.0.0 netmask 255.255.255.0

Please substitute the parameters to suite your own networking.

After that, ping each other,

ping 192.168.0.11

to verify the networking is good to go.

In order to give our DomUs valid IPs, we may use a network bridge, do as follows:

yum -y install bridge-utils
cp /etc/sysconfig/network-scripts/ifcfg-eth0 /etc/sysconfig/network-scripts/ifcfg-xenbr0

My modified and working scripts look like this, for ifcfg-xenbr0:

DEVICE=xenbr0
#HWADDR=00:24:E8:46:CC:C9
TYPE=bridge
#UUID=ff0ab497-0303-4dc3-b6f3-4a6cbd90466b
ONBOOT=yes
NM_CONTROLLED=no
BOOTPROTO=dhcp

And for ifcfg-eth0:

DEVICE=eth0
HWADDR=00:24:E8:46:CC:C9
TYPE=Ethernet
UUID=ff0ab497-0303-4dc3-b6f3-4a6cbd90466b
ONBOOT=yes
NM_CONTROLLED=no
#BOOTPROTO=dhcp
BRIDGE=xenbr0

For static IP configuration, please refer to Xen wiki page!

Then, make the configuration work:

service network restart

If you got errors such as error:check cable, do this manualy:

ifup xenbr0

Verify it works by issuing:

ifconfig xenbr0

Diable SELinux

Honestly speaking, I don’t know WTF the real reason to do this, but people say SELinux can really interfere with Xen.

sed -i 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/selinux/config
setenforce 0

You are good to go with a damn working Dom0 and congratulations!

Bringing Your DomUs Up

It’s up to you to use PV or HVM, personally, I prefer to PV due to higher performance. But if you want a Windows(and other OS whose kernel can’t be modified), HVM is your only choice.

As for me, I want 3 DomUs, namely Debian, Fedora and Arch Linux.

Xen4Cli or Xen4Libvirt

Xen4Cli(xm and xl, currently xm deprecated) are intended for advanced users looking to hand setup the network, the backing filestore and the xen environment. While Xen4Libvirt are for newbies looking for the easiest install path.

I prefer xl since I want to know what exactly is happening, and xl works for Debian and Arch Linux. However for Fedora, Libvert seems to be the right way(using virt-install).

To install Libvirt,

yum install libvirt python-virtinst libvirt-daemon-xen

After the install, restart your Dom0 machine.

File or LVM based backend

Since Centos6.4 is shipped perfectly with LVM and also the default partition schema using LVM during OS Installation, I prefer LVM.

As for me, I do the following:

lvresize -L -200G vg_centos6/lv_home -r
lvcreate -L 30G -n fedora vg_centos6
lvcreate -L 30G -n debian vg_centos6
lvcreate -L 30G -n archlinux vg_centos6

Then verify the Logical Volumes using:

lvdisplay

Or

lvs

If you are not familiar with LVM, search Google for a good tutorial first.

Bridge, Routing or NAT

Three networking modes are provided and choose one according to your own networking environment.

I got bridge working for me as described in above section.

For choosing other modes, you can modify /etc/xen/xend-config.sxp or explicitly passing as parameters when creating DomUs.

Let DomUs fly

Debian

I choose debian7.1 netinst.iso due to my poor bandwidth,

wget -c http://mirrors.sohu.com/debian-cd/7.1.0/amd64/iso-cd/debian-7.1.0-amd64-netinst.iso
mount -o loop /path/to/debian-7.1.0-amd64-netinst.iso /mnt/debian
cp /mnt/debian/install.amd/xen/debian.cfg /etc/xen/
cd /etc/xen/
vi debian.cfg  ## Make modifications according to the comments
xl create -c debian.cfg

Then install Debian as a very normal one.

Arch Linux

I download archlinux-2013.10.01-dual.iso by issuing:

wget http://mirrors.sohu.com/archlinux/iso/latest/archlinux-2013.10.01-dual.iso

Then create a arch.cfg file in /etc/xen/ similar like:

# Refer to https://wiki.archlinux.org/index.php/Xen#Configuring_a_paravirtualized_.28PV.29_Arch_domU

name = "arch"
kernel = "/mnt/arch/arch/boot/x86_64/vmlinuz"
ramdisk = "/mnt/arch/arch/boot/x86_64/archiso.img"
extra = "archisobasedir=arch archisolabel=ARCH_201310"
memory = 512
disk = [ "phy:/dev/vg_centos6/archlinux,sda1,w", "file:/root/isos/arch/archlinux-2013.10.01-dual.iso,sdb,r" ]
vif = [ '' ]

After that, bring the DomU up by:

mount /path/to/archlinux-2013.10.01-dual.iso /mnt/arch
cd /etc/xen/
xl create -c arch.cfg

Install your Arch Linux as you like since it’s really a highly customized distro.

Fedora

Again I got Fedora-20-Alpha-x86_64-netinst.iso by issuing:

wget http://download.fedoraproject.org/pub/fedora/linux/releases/test/20-Alpha/Fedora/x86_64/iso/Fedora-20-Alpha-x86_64-netinst.iso

However, nightmares begin since I want to install it using the Debian way. xl just fails to boot normally but virt-install does the job.

Using the virt-install method:

virt-install --virt-type xen -n fedora19 -r 512 --vcpus=2 -f /dev/vg_centos6/fedora19 --location http://mirrors.163.com/fedora/releases/19/Fedora/x86_64/os/ --os-type linux --accelerate --nographics --network=bridge:xenbr0

Or you can download the ISO file first, then issuing your own httpd locally, thus making it:

mount -o loop /path/to/fedora.iso /mnt/fedora
yum -y install httpd
service httpd start
ln -s /mnt/fedora /var/www/html
service iptables stop
virt-install --virt-type xen -n fedora19 -r 512 --vcpus=2 -f /dev/vg_centos6/fedora19 --location http://your.http.server.ip.address.here/ --os-type linux --accelerate --nographics --network=bridge:xenbr0

Remember this is for full Fedora installation, if you are using a netinst, you need to copy all the files to /var/www/html instead of creating a symbolic link and modify the .treeinfo file. No warrants here, since I did’t try it myself.

References


I do believe you will get lots of annoying problems while playing with Xen. Enjoy the problems and enjoy Xen:–)

Comments