LOAD BALANCING OF APPLICATIONS USING XEN HYPERVISOR

1. Xen Virtualization
Submitted To:
Mr. Prakash Kumar
Submitted By:
Vanika Kapoor(10103453)
Atishay Baid(10103457)

2. Virtualization
 Separation of administrative zones
 Separation of software failure
 Consolidation of hardware resources
Full utilization of hardware
Easier hardware provisioning -- Want a
server? You’ve got a server.
Excellent test environments

3. What virtualization isn’t
 Not an HA solution by itself
 Naïve Implementation:
 Not suitable for some secure applications
 Timing of private keys
 Unknown -- Lots of new code
 Host OS adds a new point of entry
 May actually increase complexity
 Adds Host OSes to manage
 Adds to total number of points of management
 Encourages “guerilla” server projects

4. Full Virtualization
 Hardware Virtual Machines
 VMWare, Xen HVM, KVM, Microsoft VM, Parallels
 Runs unmodified guests
 Generally worst performance, but often acceptable
 Simulates bios, communicates with VMs through
ACPI emulation, BIOS emulation, sometimes custom
drivers
 Can sometimes virtualize accross architectures,
although this is out of fashion.

5. Para-virtualization
 Hypervisor runs on the bare metal. Handles CPU
scheduling and memory compartmentalization.
 Dom0, a modified Linux Kernel, handles networking
and block storage for all guests.
 Dom0 is also privileged to manage the VMs on the system.
 DomU, or the guests OS, sends some requests
straight to the hypervisor, and others to the Dom0.
 Because the kernel knows its virtualized, features can
be built into it: hot connection/disconnection of
resources, friendly shutdown, serial console.
 Other paravirtualization schemes: Sun Logical
Domains, VMware (sometimes)

6. Elements of a Xen VM
Virtual Block Device
Image file
Real block device (either LVM or physical)
Network Bridges
Routed, terminates at the Dom0
Bridged, terminates at the network
interface
Virtual Framebuffer
VNC Server

7. Example VM Config
name = ”DomU-1"
maxmem = 512
memory = 512
vcpus = 2
bootloader = "/usr/bin/pygrub"
on_poweroff = "destroy"
on_reboot = "restart"
on_crash = "restart"
vfb = [ "type=vnc,vncunused=1,keymap=en-us" ]
disk = [ "tap:aio:/var/lib/xen/images/Centos5Image.img,xvda,w" ]
vif = [ "mac=00:16:3e:79:fd:8d,bridge=xenbr0" ]

8. xm -- Xen Manager
 Commandline tool on Dom0 for managing vms.
 Quick overview of options:
 console -- attach to a device’s console
 create -- boot a DomU from a config file
 destroy -- immediately stop a DomU
 list -- List running DomUs
 migrate -- Migrate a console to another Dom0
 pause/unpause -- akin to suspend. TCP connections will timeout
 shutdown -- Tell a DomU to shut down.
 network-attach/network-detach
 block-attach/block-detach

9. Graph View

10. Xen Live Migration
Migrate machines off during upgrades or
balance load
Set xend.conf to allow migration from
other xen Dom0s.
Machine must reside on shared storage.
Must be on the same level2 network
xm migrate -l Machine dest.ip.addr.ess

11. Shared Storage Options
 NFS
 Simple hardware failover
 well-understood configuration
 Spotty reliability history
 Block level storage (iscsi or FC)
 More complex configuration
 Multipathing
 Commercial solutions are expensive
 We’re seeing traction for open iscsi lately.

12. What to Look for In Storage
Redundant host connections
Snapshotting
Replication
Sensible Volume Management
Thin Provisioning
IP-based failover, esp. if x86 based

13. Storage Systems
 OpenFiler
Nice fronted.
Replication with DRBD
iscsi with linux iscsi-target
 OpenSolaris/ZFS
Thin provisioning
Too many ZFS features to list
StorageTek AVS -- Replication in may forms
Complex configuration
 NexentaStor
ZFS/AVS in Debian.
Rapidly Evolving
 SAN/IQ
Failover, storage virtualization, n(y) redundancy
Expensive and wickedly strict licensing
 Too Many propriety hardware systems to list

14. Network Segmentation
 802.1q VLAN tagging
 All VLANs operate on the same physical network, but
packets carry an extra tag that indicates which
network they belong in.
 Create an interface and a bridge for each vlan.
 Connect Xen DomUs to their appropriate vlan
 Configure host’s switch ports as vlan trunk ports.
 Configure router somewhere, or a layer 3 switch is
useful here.

15. Commercial Xens
Citrix XenServer
Oracle VM
VirtualIron
Typical Features:
Resource QoS
Performance trending
Physical Machine Failure detection
Pretty GUI!
API for server provisioning

16. Recovery strategies
 Mount virtual block device on Dom0
 losetup /dev/loop0 XenVBlockImage.img
 losetup -a
 kpartx -a /dev/loop0
 pvscan (if using LVM inside VM)
 vgchange -a y VolGroup00
 mount /dev/mapper/VolGroup00-LogVol00 /mnt/xen
 chroot /mnt/xen (or whatever recovery steps you take next)

17. Xen Recovery -- cont
 Boot from recovery CD as HVM
disk = [ ’tap:aio:/home/xen/domains/damsel.img,ioemu:hda,w',
'file:/home/jack/knoppix.iso,ioemu:hdc:cdrom,r' ]
builder="hvm"
extid=0
device_model="/usr/lib/xen/bin/qemu-dm"
kernel="/usr/lib/xen/boot/hvmloader"
boot="d"
vnc=1
vncunused=1
apic=0
acpi=1
 Create custom Xen Kernel OS image for rescues

18. Pitfalls
 Failure to segregate network
 802.1q and iptables firewalls everywhere
 Creating Single Points of Failure
 Make sure that VMs are clustered
 If they can’t be clustered, auto started on another
machine
 Assess reliability of shared storage
 Storage Bottlenecks
 Not planning for extra points of management
 cfengine, puppet, centralized authentication
 Less predictable performance modeling

19. Maintaining HA
Hardware will fail
Individual VMs will crash
Cluster Multiple VMs for each application
Load Balancers can be VMs too.

20. HA -- Continued
 Failure Detection, make VM restart on different
machines if a machine fails
 Make VMs migrate off a host when you shut it
down
 Build your testing system into the VM scheme.
 At least one testing system per type of host.
Diligently do all changes on that before rolling out.
 Have at least one development VM per VM cluster.
 Make sure that networking equipment and
storage is redundant too
 If running web servers, keep a physical web
server on hand to serve a “We’re sorry, come
back later” page. For mail servers, an
independant backup MX.

21. What is File System?
• A file system is a hierarchical structure (file
tree) of files and directories.
• This file tree uses directories to organize
data and programs into groups, allowing the
management of several directories and files
at one time.
• Some tasks are performed more efficiently
on a file system than on each directory
within the file system.

22. What is Network File System?
• NFS developed by SUN Microsystems for use
on its UNIX-based workstations.
• A distributed file system
• Allows users to access files and directories
located on remote computers
• But, data potentially stored on another
machine.
• NFS builds on the Open Network Computing
Remote Procedure Call (ONC RPC) system

23. Continue…
Mechanism for storing files on a network.
Allows users to ‘Share’ a directory.
NFS most commonly used with UNIX systems.
Other software platforms:
-Mac OS, Microsoft Windows, Novell NetWare, etc.
Major Goals:
-simple crash recovery
-reasonable performance :80% of a local drive

24. Versions and Variations
Version 1 and Version 2
V1 Sun used only for in-house
experimental purposes
Did not release it to the public
V2 of the protocol originally operated
entirely over UDP and was meant to keep
the protocol stateless, with locking (for
example) implemented outside of the core
protocol.
Both suffered from performance problems
Both suffered from security problems
security dependant upon IP address

25. Version 3
NFS v3 can operate across TCP as well as
UDP
Support for asynchronous writes on the
server
Obtains multiple file name, handles and
attributes
Support for 64-bit file sizes and offsets
Handle files larger than 4 gigabytes (GB)
Improves performance, and allowed it to
work more reliably across the Internet

26. Version 4
Currently version 2 and version 3
protocols are in use with version 4 under
consideration for a standard
includes more performance
improvements
Mandates strong security
introduces a stateful protocol
developed with the IETF (Internet
Engineering Task Force)

27. File
Syste
m
File
Syste
m
NFS
Client
NFS
Client
Netw
ork
NFS
Server
File
Syste
m
NFS Architecture

28. RPC request Action
GETATTR Get file attribute
SETATTR Set file attribute
LOOKUP File name search
ACCESS Check access
READ Read file
WRITE Write to the file
CREATE Create file
REMOVE Remove file
RENAME Rename file

29. stateless server and client
server can be rebooted and user on
client might be unaware of the reboot
client/server distinction occurs at the
application/user level not the system
level
highly flexible, so we need to be
disciplined in our
administration/configuration
Advantages

30. Disadvantage
uses RPC authentication
easily spoofed
filesystem data is transmitted in
cleartext
Data could be copied
Network slower than local disk
Complexity, Security issues.

31. Conclusion
New technologies open up new
possibilities for network file systems
Cost of increased traffic over Ethernet
may cause problems for xFS, cooperative
caching.