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    XEN Cluster HowTo

    I have tried to run both Debian Etch and Ubuntu 8.04 Server on the cluster

    nodes, in Dom0. I started my tests with Debian, but I had some issues with

    slow samba performance in one VM that I couldn't fix so I decided to try

    Ubuntu Server, for the first time. Both installation went OK, the main

    difference was that I used mainly source code in Debian, but only packages in

    Ubuntu. I actually ran into more problems with Ubuntu due to some early

    bugs in the 8.04 release, will describe them below as I go along.

    2011-02-27: The setup in Ubuntu was very stable and I had initially very few

    problems. I ran into some trouble later on when it turned out that my

    heartbeat in combination with XEN was negatively effected by some system

    updates. Never had time to resolve it so I eventually switch off heartbeat as it

    was just causing issues.

    Instead I have started with a new install consisting of Debian Squeeze and

    XEN version 4. I'm migrating the data upgrading one node at the time.

    Documenting the migration phase and will publish it together with a fresh

    install guide.

    Installation How to


    Linux - Ubuntu 8.04 Server

    Ubuntu - Base configuration

    Installing XEN

    Configure LVM

    Configure XEN-tools

    Using XEN-tools to install DomU

    Install and configure DRBD

    Configure DomU to use your DRBD device

    Configure DomU on your other Dom0 node

    Configure Live Migration

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    Install and Configure Heartbeat

    Bug in default xendomains script


    Linux - Ubuntu 8.04 Server

    I am not going to go through each and every step of the Ubuntu installation

    as that is really straight forward. I downloaded the 8.04 Server version from

    http://www.ubuntu.com/getubuntu/download and started the installation one

    on of the nodes.

    During disk partitioning, select manual mode and delete any existing

    partitions (if there are any).

    Create one partition for your main system and make it 5GB. This partition will

    be used for your Dom0 and 5GB should be more than enough.

    Create a second partition for your swap for Dom0. Make this 512MB as we

    later will configure Dom0 to use 512MB of RAM.

    Create a third partition with all your remaining space.

    At the packages selection step do not select any packages. Leave everything


    A few minutes later you should have a basic installation of Ubuntu 8.04

    Server running.

    Ubuntu - Base configuration

    A few things need to be done to the freshly installed Ubuntu Server before we

    start installing XEN.

    Most of the commands need to be executed with super user rights, so we

    start by typing

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    sudo su

    I installed SSH early on so I didn't need to run everything locally on theconsole

    apt-get install ssh

    Configure network interfaces for static IPs:

    nano /etc/networking/interfaces

    and configure it so it looks something like this:

    auto lo

    iface lo inet loopback

    # The primary network interface

    auto eth0

    iface eth0 inet static






    # Secondary interface used between the two clusters

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    auto eth1

    iface eth1 inet static





    This setup will use eth0 to connect to my network and eth1 as the link

    between the two nodes. For node ha2 use ip address and

    Edit /etc/hosts and add both cluster nodes

    nano /etc/hosts

    my file looks like this: localhost ha1.domain.local ha1 ha1.domain.local ha1 ha2.domain.local ha2 ha1X ha2X

    for node ha2 change the second line to ha2.domain.local ha2

    Edit the /etc/hostname file to match your Fully Qualified Domain Name

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    nano /etc/hostname


    and for node ha2 change this to: ha2.domain.local

    Reboot machine to confirm everything is working


    You should now be able to connect to your static IP address and your

    hostname should be your FQDN. Run:


    hostname -f

    and they should both return your FQDN, like this:

    [email protected]:/# hostname


    [email protected]:/# hostname -f


    Install NTP to have your time synchronized. This is important for your VMs,

    especially when migrating a VM to the other node:

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    apt-get install ntp

    Now we are done with the basic configuration of the system and can move onto the fun part, to install Xen, DRBD & Heartbeat

    Installing XEN

    I will use only packages during this installation, and installing XEN on Ubuntu

    is then a quick and hassle free process. I will only cover the important parts

    and make comments where needed, if you want to look at a more

    comprehensive guide for installing XEN on Ubuntu then please check this

    link: http://howtoforge.com/ubuntu-8.04-server-install-xen-from-ubuntu-repositories

    apt-get install ubuntu-xen-server

    Now you should have Xen installed.

    Even though you might not use loop devices in your XEN setup it can be a

    good idea to extend the number of allowed loop devices so you don't run into

    trouble later if you plan to use them. Edit /etc/module and modify the line

    with "loop" as below:

    nano /etc/modules

    loop max_loop=64

    Now it is time to reboot your system so it will boot with the new xen kernel:


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    After reboot, run:

    uname -r

    to confirm your system is using the new xen kernel. It should look like this:

    [email protected]:/# uname -r


    Configure LVM

    To install LVM run:

    apt-get install lvm2

    We will now configure a Volume Group of the third partition created during

    installation. On my system this is /dev/sda3. You can run:

    fdisk -l

    to confirm this.

    Do the following to create a volume group called "vg":

    pvcreate /dev/sda3

    vgcreate vg /dev/sda3

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    To check the status of the volume group, run:


    and then reboot:


    Within this volume group we will later create logical volumes that will be useby our VMs. You can create the logical volumes manually when installing a

    new VM, but below I will use xen-tools which will do all that for us.

    Configure XEN-tools

    If you have a cluster with two machines like me it is not necessary to

    configure xen-tools on both of them. You can decide that you always will use

    one when adding a new DomU. For flexibility I have my both machines

    configured the same way so I can run xen-tools on both.

    Xen-tools is installed automatically as part of the Xen installation above. So

    now we just need to configure it. The configuration for xen-tools is stored

    in /etc/xen-tools/xen-tools.conf


    nano /etc/xen-tools/xen-tools.conf

    and perform the following changes in the xen-tools.conf file:

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    We first uncomment the line with LVM and specify the volume group we

    created above:

    lvm = vg

    Configure the "Disk and Sizing options" section. Mine looks like this at the


    size = 5Gb # Disk image size.

    memory = 384Mb # Memory size

    swap = 384Mb # Swap size

    # noswap = 1 # Don't use swap at all for the new system.

    fs = ext3 # use the EXT3 filesystem for the disk image.

    dist = hardy # Default distribution to install.

    image = sparse # Specify sparse vs. full disk images.

    the disk size and the swap size will be used to create Logical Volumes (LVs) inyour VG specified above.

    Next we edit the "Networking" section. Mine looks like this:

    gateway =

    netmask =

    broadcast =

    we will specify the IP address of the VM and its hostname when creating the

    VM with xen-tools.

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    Uncomment the line with passwd to always be asked for the password for

    your VM. Should look like:

    passwd = 1

    As I have a 64bit AMD CPU I set the following value for my architecture:


    Next and last we change the mirrors used when installing Debian and

    Ubuntu. This is how mine looks like using mirrors in The Netherlands:

    # The default mirror for debootstrap to install Debian-derived distributions


    mirror = http://ftp.nl.debian.org/debian/


    # A mirror suitable for use when installing the Dapper release of Ubuntu.


    mirror = http://nl.archive.ubuntu.com/ubuntu/


    # If you like you could use per-distribution mirrors, which will

    # be more useful if you're working in an environment where you want

    # to regularly use multiple distributions:



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    # mirror_dapper=http://archive.ubuntu.com/ubuntu

    # mirror_edgy=http://archive.ubuntu.com/ubuntu

    # mirror_feisty=http://archive.ubuntu.com/ubuntu

    # mirror_gutsy=http://archive.ubuntu.com/ubuntu

    for Debian I had to enable the per-distribution mirrors as shown above.

    Otherwise installing sid, sarge or etch would fail.

    Now we are done configuring /etc/xen-tools/xen-tools.conf

    The default setting in xen-tools.conf is using the debootstrap installation

    method. For installing Fedora and CentOS you need to use rinse. If you want

    to try that later on you should install rinse by running:

    apt-get install rinse

    Now we are ready to use xen-tools!

    Using XEN-tools to install DomU

    Perform this step on only one of your machines, either HA1 or HA2, to create

    your first DomU.

    Time to install our first DomU. The application we use for this part of Xen-

    tools is called: xen-create-image. The only two parameters we supply when

    using xen-create-image is the IP address and hostname of the DomU. All

    other settings will be taken from xen-tools.conf. But you can override all

    these settings at command line. For example, to change the distribution you

    would write --dist=etch to install Debian etch instead of Ubuntu Hardy.

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    Now, run the following to create a DomU with IP: and with

    hostname: test:

    xen-create-image --hostname=test --ip=

    After a while the process hopefully completed successfully and your DomU is

    ready. For me it took about 5 minutes to complete.

    xen-create-image has now automatically created two LVs in your VG. If you

    used the hostname "test", you will have one LV called "test-disk" and another

    one called "test-swap". Full path to these are: "/dev/vg/test-disk" and




    and you will see the details of your two LVs.

    You should now be able to start your DomU called: test. The config files for

    your DomUs are stored in /etc/xen/. We first change to that folder:

    [email protected]:/# cd /etc/xen

    In /etc/xen/ you will find test.cfg which is the config file for your newly

    created DomU.

    Start the DomU:

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    [email protected]:/etc/xen# xm create test.cfg

    you can also add -c to the line above, that will automatically bring you to theconsole of the DomU. If you didn't, we can check the status of the running

    DomU with:

    xm list

    To change to the console of the running DomU, run:

    xm console test

    if everything went fine you will now see the prompt to login to your DomU

    test. To leave console mode in your DomU you need to press Ctrl and ]:

    Ctrl + ]

    Perfect! You now have your first virtual machine running.


    We will soon go ahead and configure DRBD and Heartbeat to allow for live

    migration and high availability. This is the fun part! But before we do that we

    need to duplicate the LV disk setup on the other machine.

    So on HA2 we need to create one LV with 5GB and another one with 384MB.


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    [email protected]:/# lvcreate -L 5G -n test-disk vg

    to create the "test-disk" with 5GB of space. We use the same name here forsimplicity, but the names doesn't need to match as we will specify that later

    in the DRBD configuration.


    [email protected]:/# lvcreate -L 384M -n test-swap vg

    to create "test-swap" with 384MB of space.

    Now we have the same disk setup on both machines.

    Install and configure DRBD

    To install DRBD run:

    apt-get install drbd8-utils

    The configuration file for DRBD is located in /etc/drbb.conf. We will now

    configure it to use the LVs we create above and later we will change the Xen

    configuration of our test DomU to use the DRBD device instead of directly the

    LV. Edit /etc/drbd.conf:

    [email protected]:/# nano /etc/drbd.conf

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    Below is a copy of my settings with all default comments removed from the


    global {

    usage-count yes;


    common {

    syncer { rate 90M; }


    resource test-disk {

    protocol C;

    startup {

    wfc-timeout 120; ## 2 min

    degr-wfc-timeout 120; ## 2 minutes.


    disk {

    on-io-error detach;


    net {


    after-sb-0pri discard-zero-changes;

    after-sb-1pri discard-secondary;

    timeout 60;

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    connect-int 10;

    ping-int 10;

    max-buffers 2048;

    max-epoch-size 2048;


    syncer {


    on ha1.domain.local {


    device /dev/drbd1;

    disk /dev/vg/test-disk;

    meta-disk /dev/vg/meta[0];


    on ha2.domain.local {


    device /dev/drbd1;

    disk /dev/vg/test-disk;

    meta-disk /dev/vg/meta[0];



    resource test-swap {

    protocol C;

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    startup {

    wfc-timeout 120; ## 2 min

    degr-wfc-timeout 120; ## 2 minutes.


    disk {

    on-io-error detach;


    net {


    after-sb-0pri discard-zero-changes;

    after-sb-1pri discard-secondary;

    timeout 60;

    connect-int 10;

    ping-int 10;

    max-buffers 2048;

    max-epoch-size 2048;


    syncer {


    on ha1.domain.local {


    device /dev/drbd2;

    disk /dev/vg/test-swap;

    meta-disk /dev/vg/meta[1];

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    on ha2.domain.local {


    device /dev/drbd2;

    disk /dev/vg/test-swap;

    meta-disk /dev/vg/meta[1];



    I have given the DRBD resource the same name as its corresponding LV. SoDRBD resource: test-disk is using LV: test-disk.

    Next we will create a separate volume where we store DRBD's meta data.

    Meta data is used by DRBD to store information about the device. This can

    either be internal or external. Internal mode is easier to setup for a new

    devices but requires resizing operations when using an already formatted

    device. Read further about this on: http://www.drbd.org/users-guide/ch-


    As we already have data on our LVs, created by XEN tools, we will use

    external meta data. So we create another LV with 1GB of space:

    lvcreate -L 1G -n meta vg

    If drbd.conf, above, you will see that we specify the line with meta-disk as

    using /dev/vg/meta[0] and /dev/vg/meta[1]. Same device can be used to

    store meta-data for several DRBD resources, that is done with adding [X]

    after the device name.

    To initiate the meta data, run:

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    drbdadm create-md test-disk

    drbdadm create-md test-swap

    Redo the DRBD configuration above for the other node if you haven't done


    Now we will startup DRBD on both nodes. Run:

    /etc/init.d/drbd start

    To check status of DRBD use the following commands:

    /etc/init.d/drbd status

    cat /proc/drbd

    Before the replication of data will begin we have to make one node the

    primary node for each DRBD resource. Run the following on the node you

    installed your DomU above to replicate the data to the other node (Do NOT

    run it on the other node):

    drbdsetup /dev/drbd1 primary -o

    drbdsetup /dev/drbd2 primary -o

    Check the status again to see that the replication started:

    /etc/init.d/drbd status

    cat /proc/drbd

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    If everything is OK after data is replicated you should see something like this

    for each DRBD device when running /etc/init.d/drbd status. It should state

    Primary/Secondary and UpToDate/UpToDate:

    /etc/init.d/drbd status

    1:test-disk Connected Primary/Secondary UpToDate/UpToDate C

    2:test-swap Connected Primary/Secondary UpToDate/UpToDate C

    Now we are done setting up the DRBD device for our LV. Next is to configureor DomU to use DRBD.

    Configure DomU to use your DRBD device

    The configuration files for your DomUs are stored in /etc/xen/. So we first

    change to that directory:

    cd /etc/xen

    In here you have your test.cfg file. Edit it by running:

    /etc/xen# nano test.cfg

    You will find a section that looks like below:

    disk = [

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    Edit this section so it looks like this:

    disk = [




    Done! That is all, now your DomU is ready to be started using the DRBD


    If your DomU is still running we first have to stop it. Run:

    xm shutdown test

    Try to start your DomU again:

    xm create test.cfg -c

    Hopefully everything went fine. Smile Login and then shutdown your DomU:

    shutdown -h now

    When you are back to your Dom0 prompt check the DRBD status again:

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    /etc/init.d/drbd status

    You will now see the status of the DRBD devices as Secondary/Secondary:

    1:test-disk Connected Secondary/Secondary UpToDate/UpToDate C

    2:test-swap Connected Secondary/Secondary UpToDate/UpToDate C

    The good thing with this is that Xen takes care of your DRBD devices and will

    automatically bring them up and down as needed. Same goes when you start

    a DomU, Xen will first make sure the DRBD devices are in primary modebefore starting the DomU.

    Configure DomU on your other Dom0 node

    Now we need to prepare the other Dom0 node to be able to run the DomU

    called test. This is simply done by copying the /etc/xen/test.cfg from ha1 toha2. Copy the whole file or the content of the file, what ever is easier for you.

    When the file is copied we will try to start the DomU on ha2.

    First make sure that DomU test is not running on ha1:

    [email protected]:/# xm list

    If it is running the stop it:

    [email protected]:/# xm shutdown test

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    Then go to ha2 and start it:

    [email protected]:/# xm create test.cfg

    If everything is fine you should see DomU test running. Check with xm list:

    [email protected]:/# xm list

    Perfect! You can now start the DomU on both nodes. (Note: Don't try to start

    the DomU on both nodes at the same time.)

    Next we will start with the real cool things!

    We will go ahead and configure live migration so we can move a DomU

    between the two Dom0 nodes with hardly any downtime. Cool

    Configure Live Migration

    By default XEN does not allow live migration, we have to enable this is

    /etc/xen/xend-config.sxp. Make sure the following line is commented, it

    should look like this:

    #(xend-relocation-hosts-allow '^localhost$ localhost\\.localdomain$')

    and that the following line is not commented, it should look like this:

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    (xend-relocation-port 8002)

    Restart xend, reload has no effect, but restart will not kill running DomUs.


    /etc/init.d/xend restart

    Make sure to do this two changes above on both nodes, both ha1 & ha2.

    NOW, lets try a live migration!

    If everything is in order your DomU called test should be running on your ha2

    node. Please confirm this with xm list:

    [email protected]:/# xm list

    Name ID Mem VCPUs State Time(s)

    Domain-0 0 500 2 r----- 10268.0

    test 7 384 1 -b---- 4694.7

    To migrate a DomU we use the xm migrate command. Run:

    [email protected]:/# xm migrate test ha1x --live

    So first we write xm migrate. Then the name of the DomU we want to

    migrate, in this case test. Then the hostname or IP of the other node, in this

    case ha1x (remember that we specified ha1x and ha2x in the hosts file on

    both nodes and mapped it to the IP of the interface with the cross over

    connection between ha1 and ha2). And we end the command with --live, that

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    will instruct xen to do a live migration.

    If everything went fine your DomU test should be running on ha1. Run:

    [email protected]:/# xm list

    Name ID Mem VCPUs State Time(s)

    Domain-0 0 500 2 r----- 10260.1

    test 11 384 1 -b---- 2.2

    Try the migration a few times between the two nodes. Try accessing the

    DomU during a live migration, ping it from another machine in your network,

    open a SSH session and see how incredible fast it migrates. I have not timed

    it myself, but running a normal ping from a Windows machine I lose no

    packets or maximum 1 packet during a migration. Smile

    Install and Configure Heartbeat

    We will use Heartbeat, part of the Linux High Availability project

    (http://www.linux-ha.org/), to monitor our XEN resources and provide failover

    between our two nodes. I currently use version 2 of hearbeat but utilizing

    versions 1's configuration files, so that is what I will describe below. Read

    more in the link above about the difference in configuration files.

    To install Heartbeat we will use package in the Ubuntu repository. Run this on

    both nodes:

    apt-get install heartbeat

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    Configuration files for Heartbeat is stored in /etc/ha.d/. We need to configure

    the following files: authkeys, haresources and ha.cf.

    We will start with configuring authkeys and ha.cf as they are the easiest to


    Authkeys is used to configure authentication between the cluster nodes.

    Configure it to look something like this:

    [email protected]:/etc/ha.d# nano authkeys

    auth 1

    1 sha1 SecretKey123!!!

    This will tell heartbeat to use the method sha1 with the supplied key. Note:

    Make sure to copy the exact same copy to your ha2 node.

    Lets continue with ha.cf. This file contains the configuration for heartbeat:

    nodes in the cluster, how they communicate and timer settings. What I will

    use is the version 1 configuration format. Configure the file to look something

    like this:

    [email protected]:/etc/ha.d# nano ha.cf

    logfacility local0

    udpport 694

    keepalive 1

    deadtime 10

    warntime 3

    initdead 20

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    ucast eth0

    ucast eth0

    auto_failback on

    watchdog /dev/watchdog

    debugfile /var/log/ha-debug

    node ha1.domain.local

    node ha2.domain.local

    The two lines above that begin with "ucast eth0 " configures the heartbeat

    communication. The reason I have put both node's IP addresses is so the file

    can be identical on both nodes, heartbeat will ignore the IP of the localmachine so this is perfectly fine. Note: Make sure to copy the exact same

    copy to your ha2 node.

    Now we will continue with haresources file. The file itself is actually very easy

    but we need to setup the resources used by heartbeat which requires some

    explanation. We begin with the file, configure it to look like this:

    [email protected]:/etc/ha.d# nano haresources

    ha1.domain.local xendomainsHA1

    ha2.domain.local xendomainsHA2

    Looks very simple, doesn't it? Smile What this means is that the

    resource(script that will control our DomUs) xendomainsHA1 will default to

    node HA1 and xendomainsHA2 to node HA2. These two scripts are copies of

    the /etc/init.d/xendomains script and modified for our two node cluster. We

    need to do this to be able to differentiate between DomUs on HA1 resp. HA2.

    First we copy the /etc/init.d/xendomains twice to create xendomainsHA1 and


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    [email protected]:/# cp /etc/init.d/xendomains /etc/ha.d/resource.d/xendomainsHA1

    [email protected]:/# cp /etc/init.d/xendomains /etc/ha.d/resource.d/xendomainsHA2

    Now we edit both files to change two lines so it looks like below:

    [email protected]:/# nano /etc/ha.d/resource.d/xendomainsHA1



    [email protected]:/# nano /etc/ha.d/resource.d/xendomainsHA2



    Please make sure that all the Heartbeat configuration above is exactly the

    same on node HA2. Below the configuration will differ slightly.

    As you noticed above we specified different configuration files for the

    resources. There is a default configuration file already located in /etc/default,

    called xendomains. We will copy it as below:

    [email protected]:/# cp /etc/default/xendomains /etc/default/xendomainsHA1

    We copy only xendomainsHA1 to begin with. We will modify it and then later

    use it for xendomainsHA2.

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    [email protected]:/# nano /etc/default/xendomainsHA1

    XENDOMAINS_MIGRATE="ha2X --live"

    This will allow for live migration to HA2 when node is shutdown.


    Disable save feature.


    Disable this to prevent ALL DomUs to be shutdown even them not

    controlled by this script


    Disable as we don't save DomUs


    Point to location for DomU configuration files that will be controlled by this



    Only DomUs started via config files in XENDOMAINS_AUTO will be managed

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    Now we copy xendomainsHA1 to create xendomainsHA2:

    [email protected]:/# cp /etc/default/xendomainsHA1 /etc/default/xendomainsHA2

    And we modify xendomainsHA2 to point to correct folder for DomU

    configuration files:

    [email protected]:/# nano /etc/default/xendomainsHA2


    Now we can copy /etc/default/xendomainsHA1 and

    /etc/default/xendomainsHA2 to node HA2. Do that by any means you want,

    either file transfer or copy and paste.

    On HA2 we need to modify the settings for live migration:

    [email protected]:/# nano /etc/default/xendomainsHA1

    XENDOMAINS_MIGRATE="ha1X --live"

    [email protected]:/# nano /etc/default/xendomainsHA2

    XENDOMAINS_MIGRATE="ha1X --live"

    Next we need to create the two folders /etc/xen/auto/HA1 and

    /etc/xen/auto/HA2 as referred above. Do this on both node HA1 & HA2.

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    mkdir /etc/xen/auto/HA1

    mkdir /etc/xen/auto/HA2

    Create a symlink on both nodes in /etc/xen/auto/HA1 pointing to our test.cfg

    file in /etc/xen/

    ln -s /etc/xen/test.cfg /etc/xen/auto/HA1/test

    Whenever creating a new DomU you need to decide if you want it by default

    to run on HA1 or HA2, the location of the symlink will decide that.

    Remove the default xendomains script to start automatically, heartbeat will

    now control this for us. Do this on both nodes:

    update-rc.d -f xendomains remove

    Shutdown DomU test if it is running:

    xm shutdown test

    Start heartbeat manually on both nodes:

    /etc/init.d/heartbeat start

    Hopefully everything is fine. Try to reboot one node at a time to see that

    DomU test is migrated between the two nodes.

    Bug in default xendomains script

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    There is a bug in the default xendomains script that breaks the script if there

    are more than one domain in the AUTO directory. This is only true for non

    standard configurations like mine above when

    XENDOMAINS_AUTO_ONLY=true in /etc/defaults/xendomains. By default thissetting is false hence I guess no one picked up on it. Been too lazy to create a

    patch for it but I will try to get around and do that.


    The rdnames() function now looks like this:




    if ! contains_something "$XENDOMAINS_AUTO"




    for dom in $XENDOMAINS_AUTO/*; do

    rdname $dom

    if test -z "$NAMES"; then







  • 8/3/2019 Xen Clustering


    And the beginning of the stop() function look likes this:



    # Collect list of domains to shut down

    if test "$XENDOMAINS_AUTO_ONLY" = "true"; then



    echo -n "Shutting down Xen domains:"

    while read LN; do

    parseln "$LN"

    if test "$id" = "0"; then continue; fi

    echo -n " $name"


    if test "$XENDOMAINS_AUTO_ONLY" = "true"; then

    for i in ${NAMES[@]}


    if test $found="0"; then

    if test $i = $name; then





    if test $found = "0"; then

    echo -n "(skip)"

  • 8/3/2019 Xen Clustering





    # XENDOMAINS_SYSRQ chould be something like just "s"

    This script shall now work for more than one DomU. Smile


    Here is a string I use in my Dom0 to check relevant logs of the system, xen

    and heartbeat. Keep this running in a separate shell when testing migration

    and heartbeat failover:

    tail -f /var/log/syslog /var/log/xen/xend.log /var/log/xen/xend-debug.log