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 DormU 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 DormU 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

    @@ -135 +135 @@
             for subnet in $subnet_list; do
               cat <<EOF >> $nfs_exports
     $drbl_common_root $subnet.*($EXPORTS_NFS_RO_NRS_OPT)
    +/root $subnet.*($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)
    @@ -169 +170 @@
             for ip in `get-client-ip-list`; do
               cat <<EOF >> $nfs_exports
     $drbl_common_root $ip($EXPORTS_NFS_RO_NRS_OPT)
    +/root $ip($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

    @@ -214 +214 @@
     $nfsserver:$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
      

  • 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 DormU configure files

• Use xen-create-image command to create new DormU 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
  

Reference

• ​Syslinux Wiki
• ​Xen PXE Boot Howto
• ​Bootloader support for Xen
• If you are using debian, beware of bug ​#391152
• ​A Time Machine and File Server with RAID, Samba and Xen (PDF)