Xen on 4 app servers
Objective
To have four application servers which will be running on top of Xen. These servers will have Debian as their operating system. These four servers will be hosting the applications which are critical to the functioning of organization. We are going to demonstrate how this is possible using Xen and Debian Linux distribution and Apache2.
System Description: Dell PowerEdge R710,Debian (amd64), 500GB Hard disk, 8GB RAM, Quad Core Processor.
Key Terms: Virtualization, Reverse Proxy on Apache2
Who should read this document:
- People/Organizations who want to have different servers for each application which will be dedicated to those applications without buying a separate hardware for these servers.
- System administrators who are new to Linux on Xen.
- Any one who is interested in testing virtualization.
- Curious people
Before you go to read this document familiarize yourself with DNS, Gateway and some basic networking stuff. Those who want to go a level higher they should learn how to use iptables on Linux.
What is virtualization?
- Virtualization is the name given to a concept where in you run multiple operating systems, at the same time, on one computer.
- Rather than running operating systems on the hardware, a small layer of software, called a hypervisor, runs between the operating system and hardware. The hypervisor's role is to provide a platform that can run multiple operating systems concurrently.
- These guest operating systems can be Windows, Linux, Solaris or any other operating system.
Test Infrastructure and Network
We are going to install Debian on a Dell PowerEdge R710 Server. We have a network whose configuration is as follows
Dom0 with IP 192.168.0.100 DomU1 with IP 192.168.0.11 DomU2 with IP 192.168.0.12 DomU3 with IP 192.168.0.13 DomU4 with IP 192.168.0.14
All of these have a subnet mask of 255.255.255.0 and 192.168.0.1 is the gateway
Preparing the base system Dom0
Follow instructions at http://www.debian.org/releases/stable/installmanual to install the latest Debian version.
Installing Xen on Debian
There are two ways to install Xen.
- Compile Xen from sources. See [[1]]
- Install a precompiled binary package.
We have chosen the second approach.
apt-get install xen-linux-system dpkg-divert --divert /etc/grub.d/08_linux_xen --rename /etc/grub.d/20_linux_xen update-grub
Setup networking. See Host_Configuration/Networking.
Creating LVM based DomU Images on Xen for Debian
Before we go on to proceed with LVM based images we will check for the LVM setup.You can skip this section if you have already set a LVM based setup and go to Creation of LVM based images.
- Check your hard disk structure
dom0#fdisk -l
Device Boot Start End Blocks Id System
/dev/sda1 1 1216 9767488+ 83 Linux
/dev/sda2 1217 60801 478616512+ 5 Extended
/dev/sda5 1217 4863 29294496 82 Linux swap / Solaris
/dev/sda6 4864 17021 97659103+ 83 Linux
/dev/sda7 17022 29179 97659103+ 83 Linux
/dev/sda8 29180 41337 97659103+ 83 Linux
/dev/sda9 41338 60801 156344548+ 83 Linux
- First you need to install LVM:
apt-get install lvm2
- Add each disk partition as a physical volume, into LVM.
dom0#pvcreate /dev/sda6 /dev/sda7 /dev/sda8 /dev/sda9
Physical volume "/dev/sda6" successfully created
Physical volume "/dev/sda7" successfully created
Physical volume "/dev/sda8" successfully created
Physical volume "/dev/sda9" successfully created
You can run pvdisplay to learn about the current state of your physical volumes.
dom0:~# pvdisplay
--- Physical volume ---
PV Name /dev/sda6
VG Name
PV Size 93.13 GB / not usable 2.22 MB
Allocatable yes
PE Size (KByte) 4096
Total PE 23842
Free PE 128
Allocated PE 23714
PV UUID l8lIGR-246n-js5p-bb6y-w2zI-XCdy-r6H2CY
--- Physical volume ---
PV Name /dev/sda7
VG Name
PV Size 93.13 GB / not usable 2.22 MB
Allocatable yes (but full)
PE Size (KByte) 4096
Total PE 23842
Free PE 0
Allocated PE 23842
PV UUID m6eqKv-ud3V-TJP2-p9E3-k4FK-3SxM-ZSzKrz
--- Physical volume ---
PV Name /dev/sda8
VG Name
PV Size 93.13 GB / not usable 2.22 MB
Allocatable yes (but full)
PE Size (KByte) 4096
Total PE 23842
Free PE 0
Allocated PE 23842
PV UUID DGGrt0-Bxhn-JmYc-lq2O-acw8-DAt3-KaPC7P
--- Physical volume ---
PV Name /dev/sda9
VG Name
PV Size 149.10 GB / not usable 228.50 KB
Allocatable yes (but full)
PE Size (KByte) 4096
Total PE 38170
Free PE 0
Allocated PE 38170
PV UUID 6ushwj-9Rse-cGGu-RXDk-2vTe-uSbw-6N5R42
Now we will create our volume group virtualization and add /dev/sda6 - /dev/sda7- /dev/sda8 /dev/sda9
dom0:~# vgcreate virtualization /dev/sda6 /dev/sda7 /dev/sda8 /dev/sda9
Volume group "virtualization" successfully created
dom0:~# vgscan
Reading all physical volumes. This may take a while...
Found volume group "virtualization" using metadata type lvm2
Follow the instructions for installing a Debian guest, [[2]]
To use the newly created guest, execute
xl create -c /etc/xen/debian.cfg
To shut down the guest, execute
xl shutdown debian
in dom0.
For more commands you can use xl help. For example, if you have four different DomU's installed, this will show:
dom0:~# xl list
Name ID Mem VCPUs State Time(s)
Domain-0 0 875 8 r----- 361.4
domu1 7 3072 4 -b---- 32.9
domu2 9 1024 4 -b---- 32.0
domu3 8 1024 4 -b---- 34.0
domu4 6 2048 4 -b---- 32.2
If you want domu1 to start automatically at the next boot of the system, then execute:
ln -s /etc/xen/domu1.cfg /etc/xen/auto
Configuration files
A sample configuration file for domU looks like this
kernel = '/boot/vmlinuz-3.5.0'
ramdisk = '/boot/initrd.img-3.5.0'
memory = '2048'
#
# Disk device(s).
#
disk = [
'phy:/dev/virtualization/domu1-swap,xvda1,w',
'phy:/dev/virtualization/domu1-disk,xvda2,w',
]
#
# Hostname
#
name = 'domu1'
#
# Networking
#
vif = [ 'ip=192.168.0.11,mac=00:16:3E:66:03:E1' ]
#
# Behaviour
#
on_poweroff = 'destroy'
on_reboot = 'restart'
on_crash = 'restart'
vcpus = '4'
Setting up Networking
We are now going to set up each of our guests with networking. Each will have its own IP address. The result of this setup will look like:
IP of Domu1:192.168.0.11 Lets call it as a
IP of Domu2:192.168.0.12 Lets call it as b
IP of Domu3:192.168.0.13 Lets Call it as c
IP of Domu4:192.168.0.14 Lets Call it as d
Ip of Dom0 :192.168.0.100 (Will behave as Gateway for DomU's)
Lets call Dom0 as A
Gateway for the network is 192.168.0.1
We will call it as G.
We have to enable IP forwarding for the hosts to appear on network:
dom0:~# echo 1 > /proc/sys/net/ipv4/ip_forward
In /etc/sysctl.conf uncomment net.ipv4.ip_forward=1
Now your hosts should appear on network. Inspite of the fact that that a,b,c,d are DomU's they are available on network as actual machines.
DNS should point to actual DNS of your network since with IP Forwarding enabled the DomU's will be able to access the proxy and rest of the network.
Now since you have enabled IP Forwarding so you should be able to ping from any other machine to you DomU's to make sure the things are working as expected you ping from C to a you should get a reply.
ping 192.168.0.11
PING 192.168.0.11 (192.168.0.11) 56(84) bytes of data.
64 bytes from 192.168.0.11: icmp_seq=1 ttl=64 time=3.32 ms
64 bytes from 192.168.0.11: icmp_seq=2 ttl=64 time=0.045 ms
^C
--- 192.168.0.11 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1008ms
rtt min/avg/max/mdev = 0.045/1.685/3.326/1.641 ms
So DomU1 is accessible from C and in turn from the rest of the network. If you experience problems, ensure you have enabled ip forwarding in Dom0.
Xen has a default network managment which will create a bridge whose name will be same as your interface name. Follow instructions at Network_Configuration_Examples_(Xen_4.1+).
Install applications
Now follow instructions to install and configure your desired applications.
Check points and possible errors
- Before you choose to install separate OS as DomU's calculte the amount of RAM they consume and swap space that to allocate them. When Dom's run they require a certain amount of memory to be allocated to them. Suppose you have 8 GB RAM and you decide to give 2GB Ram to each of the virtual hosts, you create then you won't be left with memory for Dom0. We planned to give 875 Mb memory to the Dom0 so we were left with 8192-875=7317Mb of Ram which we planned to give to the DomU's. The memory assigned to each domain is shown by the command xl list.
dom0:~# xl list
Name ID Mem VCPUs State Time(s)
Domain-0 0 875 8 r----- 361.4
domu1 7 3072 4 -b---- 32.9
domu2 9 1024 4 -b---- 32.0
domu3 8 1024 4 -b---- 34.0
domu4 6 2048 4 -b---- 32.2
Where domu1,domu2,domu3,domu4 are different dom's running.
If you encounter any problem doing above or want to give some suggestion that can be added in this page drop me a mail Tapas: mightydreams@gmail.com
