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Massive Deployment of Xen enabled Virtual Cluster using Diskless …

Massive Deployment of Xen enabled Virtual Cluster using Diskless Remote Boot Linux

Test Environment

VMWare Server 1.0.3
VMWare Image debian 4.0r1 as DRBL Server
VMWare Image without disk as DRBL Client

Pre-installation

First, install Xen Hypervisor and Xen enabled Linux Kernel and then reboot

root@drbl-xen-srv:~# uname -a
root@drbl-xen-srv:~# mv /lib/tls /lib/tls.disabled
root@drbl-xen-srv:~# echo "loop max_loop=255" >> /etc/modules
Linux drbl-xen-srv 2.6.18-6-686 #1 SMP Sat May 24 10:24:42 UTC 2008 i686 GNU/Linux
root@drbl-xen-srv:~# apt-get install xen-hypervisor-3.0.3-1-i386-pae linux-image-2.6.18-6-xen-vserver-686 xen-tools libc6-xen bridge-utils
root@drbl-xen-srv:~# update-grub
root@drbl-xen-srv:~# reboot

Note1: If you did not install libc6-xen, "4gb seg fixup" error message will keep showing up while booting.
Note2: amd64 architecture does not have libc6-xen package (i386 only)
Note3: disable tls for libc6-xen
```
root@drbl-xeb-srv:/lib# dpkg -S /lib/tls
libc6-xen, libc6: /lib/tls
```
- [FYI] Reload this Page what is the meaning of /lib/tls directory?
Note4: Xen will use loop device for creating new DomU machine, so we load loop kernel module while booting.

Choose Xen to boot at GRUB menu

Install and Configure DRBL

Download GPG-KEY-DRBL and add GPG key via apt-key

root@drbl-xen-srv:~# wget http://drbl.nchc.org.tw/GPG-KEY-DRBL
root@drbl-xen-srv:~# apt-key add GPG-KEY-DRBL

Add DRBL repository URL to /etc/apt/sources.list.d/ then install drbl package

root@drbl-xen-srv:~# echo "deb http://free.nchc.org.tw/drbl-core drbl stable" > /etc/apt/sources.list.d/drbl-sources.list
root@drbl-xen-srv:~# apt-get update
root@drbl-xen-srv:~# apt-get install drbl

Use drblsrv command to setup DRBL server. Here we choose linux-image-2.6.18-6-486 as default DRBL PXE kernel image

root@drbl-xen-srv:~# /opt/drbl/sbin/drblsrv -i 
[....skip....]
Install kernel for clients... ...
In ayo repository, searching the latest kernel ...
*****************************************************.
Now run: /opt/drbl/sbin/drblsrv-offline -c -d -a -l en_US -k /var/cache/apt/archives/linux-image-2.6.18-6-486_2.6.18.dfsg.1-18etch5_i386.deb "" ""
Kernel package /var/cache/apt/archives/linux-image-2.6.18-6-486_2.6.18.dfsg.1-18etch5_i386.deb is used for client...
*****************************************************.
[....skip....]

Use drblpush command to deploy DRBL Client Image

root@drbl-xen-srv:~# /opt/drbl/sbin/drblpush -i

Use Thin Client VMWare Image to test DRBL

Configure PXELinux for Xen Network Booting

To load Xen-based kernels you have to use the SYSLINUX multiboot module mboot.c32. So we copy mboot.c32 and Xen hypervisor to TFTP root directory of DRBL.

root@drbl-xen-srv:~# dpkg -S mboot.c32
syslinux: /usr/lib/syslinux/mboot.c32
root@drbl-xen-srv:~# cp /usr/lib/syslinux/mboot.c32 /tftpboot/nbi_img/.
root@drbl-xen-srv:~# cp /boot/xen-3.0.3-1-i386-pae.gz /tftpboot/nbi_img/.

Use drblsrv-offline command to generate initial ramdisk of xen-based kernel which is needed for PXE network booting. You should find initrd-pxe.2.6.18-6-xen-vserver-686.img and vmlinuz-2.6.18-6-xen-vserver-686 in /tftpboot/nbi_img/ folder.
```
root@drbl-xen-srv:~# /opt/drbl/sbin/drblsrv-offline -s `uname -r`
root@drbl-xen-srv:~# find /tftpboot/nbi_img/ -name "*-xen*"
/tftpboot/nbi_img/initrd-pxe.2.6.18-6-xen-vserver-686.img
/tftpboot/nbi_img/vmlinuz-2.6.18-6-xen-vserver-686
```
- Note: initrd-pxe.2.6.18-6-xen-vserver-686.img is different from /boot/initrd.img-2.6.18-6-xen-vserver-686. In initrd-pxe.2.6.18-6-xen-vserver-686.img, there are NFS mounting scripts which is needed for each DRBL client.

Since Xen-based kernel can not boot with Xen hypervisor, we have to switch vmlinuz-pxe and initrd-pxe.img back to normal linux kernl.

root@drbl-xen-srv:~# /opt/drbl/sbin/drblsrv-offline -c -d -a -l en_US -k /var/cache/apt/archives/linux-image-2.6.18-6-486_2.6.18.dfsg.1-18etch5_i386.deb

Note: You can simply remove and recreate the symbolic links named by vmlinuz-pxe and initrd-pxe.img in /tftpboot/nbi_img

root@drbl-xen-srv:~# cd /tftpboot/nbi_img
root@drbl-xen-srv:/tftpboot/nbi_img# rm initrd-pxe.img vmlinuz-pxe
root@drbl-xen-srv:/tftpboot/nbi_img# ln -s initrd-pxe.2.6.18-6-486.img initrd-pxe.img
root@drbl-xen-srv:/tftpboot/nbi_img# ln -s vmlinuz-2.6.18-6-486 vmlinuz-pxe

Add a new Xen option to pxelinux.cfg

root@drbl-xen-srv:~# cat << EOF >> /tftpboot/nbi_img/pxelinux.cfg/default
> label xen cluster
>   MENU DEFAULT
>   # MENU HIDE
>   MENU LABEL Xen 3.0.1-1-i386-pae
>   # MENU PASSWD
>   kernel mboot.c32
>   append xen-3.0.3-1-i386-pae.gz --- vmlinuz-2.6.18-6-xen-vserver-686 root=/dev/sda1 ro console=tty0 --- initrd-pxe.2.6.18-6-xen-vserver-686.img
>   TEXT HELP
>   Run Xen 3.0 in each DRBL Client
>   ENDTEXT
> EOF

Use dcs to switch PXE menu

drbl-xen-srv:~# /opt/drbl/sbin/dcs more switch-pxe-menu

Use Thin Client VMWare Image to test DRBL

Enable Xend in default rcX.d

You can run /etc/init.d/xend start manually to start xen service for each DRBL clients via drbl-doit command.
```
root@drbl-xeb-srv:~# /opt/drbl/bin/drbl-doit /etc/init.d/xend start
```

You can check the status of xend by running xm list

root@drbl-xeb-srv:~# /opt/drbl/bin/drbl-doit /usr/sbin/xm list

To save your time, we recommand you to add xend to default rcX.d by running update-rc.d xend defaults
```
root@drbl-xeb-srv:~# /opt/drbl/bin/drbl-doit /usr/sbin/update-rc.d xend defaults
```

Know Issue of DRBL () with Xen

Issue 1: Xen DomU Client will need /boot which in only on DRBL Server

Step 1: patch /opt/drbl/sbin/drbl-nfs-exports

/opt/drbl/sbin/drbl-nfs-exports

-                      old
+                      new
         for subnet in $subnet_list; do
           cat <<EOF >> $nfs_exports
 $drbl_common_root $subnet.*($EXPORTS_NFS_RO_NRS_OPT)
+/boot $subnet.*($EXPORTS_NFS_RO_NRS_OPT)
 /usr $subnet.*($EXPORTS_NFS_RO_NRS_OPT)
 /opt $subnet.*($EXPORTS_NFS_RO_NRS_OPT)
 /home $subnet.*($EXPORTS_NFS_RW_NRS_OPT)
 …
         for ip in `get-client-ip-list`; do
           cat <<EOF >> $nfs_exports
 $drbl_common_root $ip($EXPORTS_NFS_RO_NRS_OPT)
+/boot $ip($EXPORTS_NFS_RO_NRS_OPT)
 /usr $ip($EXPORTS_NFS_RO_NRS_OPT)
 /opt $ip($EXPORTS_NFS_RO_NRS_OPT)
 /home $ip($EXPORTS_NFS_RW_NRS_OPT)

step 2: patch /opt/drbl/sbin/drbl-gen-client-files

/opt/drbl/sbin/drbl-gen-client-files

-                      old
+                      new
 $nfsserver:$drblroot/$ip/etc      /etc    nfs     $FSTAB_NFS_RW_OPT
 $nfsserver:$drblroot/$ip/var      /var    nfs     $FSTAB_NFS_RW_OPT
 $nfsserver:$drblroot/$ip/root     /root   nfs     $FSTAB_NFS_RW_OPT
+$nfsserver:/boot            /tmp/boot   nfs    $FSTAB_NFS_RO_OPT
 $nfsserver:/usr             /usr        nfs    $FSTAB_NFS_RO_OPT
 $nfsserver:/opt             /opt        nfs    $FSTAB_NFS_RO_OPT
 $nfsserver:/home            /home       nfs    $FSTAB_NFS_RW_OPT

Step 3: creat a shell script to mount /boot for each node.

root@drbl-xeb-srv:~# vi mount_boot
root@drbl-xeb-srv:~# /opt/drbl/sbin/drbl-cp-host mount_boot /etc/init.d/
root@drbl-xeb-srv:~# /opt/drbl/sbin/drbl-client-service mount_boot on

Here is mount_boot

#! /bin/sh
set -e

# /etc/init.d/mount_boot: mount /boot for DRBL Client which is Xen enabled.

export PATH="${PATH:+$PATH:}/usr/sbin:/sbin"

case "$1" in
  start)
        mkdir -p /tmp/boot
        echo -n "mounting /boot:"
        mount /boot
        echo "[OK]"
        ;;
  stop)
        echo -n "unmounting /boot:"
        umount /boot
        echo "[OK]"
        ;;

  *)
        echo "Usage: /etc/init.d/ssh {start|stop}"
        exit 1
esac

exit 0

[Note 1] The "/boot" problem had been fixed by DRBL version 1.9.1-5

[Note 2] You can also modify "/opt/drbl/conf/client-append-fstab" for adding new mount point for each nodes. You can check the offical document for more detail.

If all the clients have their local harddisk, and the partition is formated (For example, /dev/hda1, its filesystem is ext3), then if you want the client to mount /dev/hda1 as /localwork when booting. Therefore you can edit /opt/drbl/conf/client-append-fstab, and its syntax is just like /etc/fstab. In this example, you can make /opt/drbl/conf/client-append-fstab like this:
/dev/hda1 /localwork ext3 defaults 0 0
(PS: You do not have to create the directory /tftpboot/node_root/localwork in DRBL server manually, later drblpush will do that for you)

Step 4: run /opt/drbl/sbin/dcs -> re-deploy or /opt/drbl/sbin/drblpush -c /etc/drbl/drblpush.conf to replace current /etc/exports.

Create Xen DomU configure files

Use xen-create-image command to create new DomU image

root@drbl-xen-srv:~# ssh 192.168.0.2
root@pc002:~# xen-create-image -dir /home/xen --dist etch --debootstrap --fs reiserfs --accounts --kernel /boot/vmlinuz-2.6.18-6-xen-vserver-686 --initrd /boot/initrd.img-2.6.18-6-xen-vserver-686 --hostname etch1 --dhcp --mirror http://free.nchc.org.tw/debian
root@pc002:~# xm create etch1.cfg
root@pc002:~# xm list

Xen DomU PXE Booting

According to "How-to boot a Xen HVM via PXE" and "pypxeboot", there are possibilities to boot Xen DomU via PXE.

Case 1: HVM supported

Case 2: only Para-Virtualization supported

Reference

Syslinux Wiki
Xen PXE Boot Howto
Bootloader support for Xen
How-to boot a Xen HVM via PXE
pypxeboot
If you are using debian, beware of bug #391152
A Time Machine and File Server with RAID, Samba and Xen (PDF)

Last modified 16 years ago Last modified on May 4, 2009, 10:46:39 AM

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