Ganeti installation tutorial

Table of Contents
1. Introduction
2. Installing the base system and base components
2.1. Hardware requirements
2.2. Installing the base system
2.2.1. Hostname issues
2.3. Installing Xen
2.3.1. Xen settings
2.3.2. Selecting the instance kernel
2.4. Installing DRBD
2.5. Other required software
3. Setting up the environment for Ganeti
3.1. Configuring the network
3.2. Configuring LVM
3.3. Installing Ganeti
3.4. Installing the Operating System support packages
3.5. Initializing the cluster
3.6. Joining the nodes to the cluster
3.7. Separate replication network
3.8. Testing the setup
4. Setting up and managing virtual instances
4.1. Setting up virtual instances
4.2. Managing virtual instances

Documents Ganeti version 1.2

1. Introduction

Ganeti is a cluster virtualization management system based on Xen. This document explains how to bootstrap a Ganeti node (Xen dom0), create a running cluster and install virtual instance (Xen domU). You need to repeat most of the steps in this document for every node you want to install, but of course we recommend creating some semi-automatic procedure if you plan to deploy Ganeti on a medium/large scale.

A basic Ganeti terminology glossary is provided in the introductory section of the Ganeti administrator's guide. Please refer to that document if you are uncertain about the terms we are using.

Ganeti has been developed for Linux and is distribution-agnostic. This documentation will use Debian Etch as an example system but the examples can easily be translated to any other distribution. You are expected to be familiar with your distribution, its package management system, and Xen before trying to use Ganeti.

This document is divided into two main sections:

Each of these is divided into sub-sections. While a full Ganeti system will need all of the steps specified, some are not strictly required for every environment. Which ones they are, and why, is specified in the corresponding sections.

2. Installing the base system and base components

2.1. Hardware requirements

Any system supported by your Linux distribution is fine. 64-bit systems are better as they can support more memory.

Any disk drive recognized by Linux (IDE/SCSI/SATA/etc.) is supported in Ganeti. Note that no shared storage (e.g. SAN) is needed to get high-availability features. It is highly recommended to use more than one disk drive to improve speed. But Ganeti also works with one disk per machine.

2.2. Installing the base system

Mandatory on all nodes.

It is advised to start with a clean, minimal install of the operating system. The only requirement you need to be aware of at this stage is to partition leaving enough space for a big (minimum 20GiB) LVM volume group which will then host your instance filesystems. The volume group name Ganeti 1.2 uses (by default) is xenvg.

While you can use an existing system, please note that the Ganeti installation is intrusive in terms of changes to the system configuration, and it's best to use a newly-installed system without important data on it.

Also, for best results, it's advised that the nodes have as much as possible the same hardware and software configuration. This will make administration much easier.

2.2.1. Hostname issues

Note that Ganeti requires the hostnames of the systems (i.e. what the hostname command outputs to be a fully-qualified name, not a short name. In other words, you should use as a hostname and not just node1.

Debian. Note that Debian Etch configures the hostname differently than you need it for Ganeti. For example, this is what Etch puts in /etc/hosts in certain situations:       localhost node1
but for Ganeti you need to have:       localhost node1
replacing with your node's address. Also, the file /etc/hostname which configures the hostname of the system should contain and not just node1 (you need to run the command /etc/init.d/ start after changing the file).

2.3. Installing Xen

Mandatory on all nodes.

While Ganeti is developed with the ability to modularly run on different virtualization environments in mind the only one currently useable on a live system is Xen. Supported versions are: 3.0.3, 3.0.4, 3.1.

Please follow your distribution's recommended way to install and set up Xen, or install Xen from the upstream source, if you wish, following their manual.

After installing Xen you need to reboot into your Xen-ified dom0 system. On some distributions this might involve configuring GRUB appropriately, whereas others will configure it automatically when you install Xen from a package.

Debian. Under Debian Etch or Sarge+backports you can install the relevant xen-linux-system package, which will pull in both the hypervisor and the relevant kernel. Also, if you are installing a 32-bit Etch, you should install the libc6-xen package (run apt-get install libc6-xen).

2.3.1. Xen settings

It's recommended that dom0 is restricted to a low amount of memory (512MiB is reasonable) and that memory ballooning is disabled in the file /etc/xen/xend-config.sxp by setting the value dom0-min-mem to 0, like this: (dom0-min-mem 0)

For optimum performance when running both CPU and I/O intensive instances, it's also recommended that the dom0 is restricted to one CPU only, for example by booting with the kernel parameter nosmp.

Debian. Besides the ballooning change which you need to set in /etc/xen/xend-config.sxp, you need to set the memory and nosmp parameters in the file /boot/grub/menu.lst. You need to modify the variable xenhopt to add dom0_mem=512M like this:

## Xen hypervisor options to use with the default Xen boot option
# xenhopt=dom0_mem=512M
and the xenkopt needs to include the nosmp option like this:
## Xen Linux kernel options to use with the default Xen boot option
# xenkopt=nosmp
Any existing parameters can be left in place: it's ok to have xenkopt=console=tty0 nosmp, for example. After modifying the files, you need to run:

2.3.2. Selecting the instance kernel

After you have installed Xen, you need to tell Ganeti exactly what kernel to use for the instances it will create. This is done by creating a symlink from your actual kernel to /boot/vmlinuz-2.6-xenU, and one from your initrd to /boot/initrd-2.6-xenU. Note that if you don't use an initrd for the domU kernel, you don't need to create the initrd symlink.

Debian. After installation of the xen-linux-system package, you need to run (replace the exact version number with the one you have):

cd /boot
ln -s vmlinuz-2.6.18-5-xen-686 vmlinuz-2.6-xenU
ln -s initrd.img-2.6.18-5-xen-686 initrd-2.6-xenU

2.4. Installing DRBD

Recommended on all nodes: DRBD is required if you want to use the high availability (HA) features of Ganeti, but optional if you don't require HA or only run Ganeti on single-node clusters. You can upgrade a non-HA cluster to an HA one later, but you might need to export and re-import all your instances to take advantage of the new features.

Supported DRBD version: the 0.7 series. It's recommended to have at least version 0.7.24 if you use udev since older versions have a bug related to device discovery which can be triggered in cases of hard drive failure.

Now the bad news: unless your distribution already provides it installing DRBD might involve recompiling your kernel or anyway fiddling with it. Hopefully at least the Xen-ified kernel source to start from will be provided.

The good news is that you don't need to configure DRBD at all. Ganeti will do it for you for every instance you set up. If you have the DRBD utils installed and the module in your kernel you're fine. Please check that your system is configured to load the module at every boot, and that it passes the following option to the module: minor_count=64 (this will allow you to use up to 32 instances per node).

Debian. You can just install (build) the DRBD 0.7 module with the following commands (make sure you are running the Xen kernel):

apt-get install drbd0.7-module-source drbd0.7-utils
m-a update
m-a a-i drbd0.7
echo drbd minor_count=64 >> /etc/modules
modprobe drbd minor_count=64

2.5. Other required software

Besides Xen and DRBD, you will need to install the following (on all nodes):

These programs are supplied as part of most Linux distributions, so usually they can be installed via apt or similar methods. Also many of them will already be installed on a standard machine.

Debian. You can use this command line to install all of them:

# apt-get install lvm2 ssh bridge-utils iproute iputils-arping \
  fping python2.4 python-twisted-core python-pyopenssl openssl \

3. Setting up the environment for Ganeti

3.1. Configuring the network

Mandatory on all nodes.

Ganeti relies on Xen running in "bridge mode", which means the instances network interfaces will be attached to a software bridge running in dom0. Xen by default creates such a bridge at startup, but your distribution might have a different way to do things.

Beware that the default name Ganeti uses is xen-br0 (which was used in Xen 2.0) while Xen 3.0 uses xenbr0 by default. The default bridge your Ganeti cluster will use for new instances can be specified at cluster initialization time.

Debian. The recommended Debian way to configure the Xen bridge is to edit your /etc/network/interfaces file and substitute your normal Ethernet stanza with the following snippet:

auto xen-br0
iface xen-br0 inet static
        address YOUR_IP_ADDRESS
        netmask YOUR_NETMASK
        network YOUR_NETWORK
        broadcast YOUR_BROADCAST_ADDRESS
        gateway YOUR_GATEWAY
        bridge_ports eth0
        bridge_stp off
        bridge_fd 0

The following commands need to be executed on the local console

ifdown eth0
ifup xen-br0

To check if the bridge is setup, use ip and brctl show:

# ip a show xen-br0
9: xen-br0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc noqueue
    link/ether 00:20:fc:1e:d5:5d brd ff:ff:ff:ff:ff:ff
    inet brd scope global xen-br0
    inet6 fe80::220:fcff:fe1e:d55d/64 scope link
       valid_lft forever preferred_lft forever

# brctl show xen-br0
bridge name     bridge id               STP enabled     interfaces
xen-br0         8000.0020fc1ed55d       no              eth0

3.2. Configuring LVM

Mandatory on all nodes.


The volume group is required to be at least 20GiB.

If you haven't configured your LVM volume group at install time you need to do it before trying to initialize the Ganeti cluster. This is done by formatting the devices/partitions you want to use for it and then adding them to the relevant volume group:

pvcreate /dev/sda3
vgcreate xenvg /dev/sda3
pvcreate /dev/sdb1
pvcreate /dev/sdc1
vgcreate xenvg /dev/sdb1 /dev/sdc1

If you want to add a device later you can do so with the vgextend(8) command:

pvcreate /dev/sdd1
vgextend xenvg /dev/sdd1

Optional. It is recommended to configure LVM not to scan the DRBD devices for physical volumes. This can be accomplished by editing /etc/lvm/lvm.conf and adding the /dev/drbd[0-9]+ regular expression to the filter variable, like this:

    filter = [ "r|/dev/cdrom|", "r|/dev/drbd[0-9]+|" ]

3.3. Installing Ganeti

Mandatory on all nodes.

It's now time to install the Ganeti software itself. Download the source from

tar xvzf ganeti-1.2b1.tar.gz
cd ganeti-1.2b1
./configure --localstatedir=/var
make install
mkdir /srv/ganeti/ /srv/ganeti/os /srv/ganeti/export

You also need to copy the file docs/examples/ganeti.initd from the source archive to /etc/init.d/ganeti and register it with your distribution's startup scripts, for example in Debian:

update-rc.d ganeti defaults 20 80

In order to automatically restart failed instances, you need to setup a cron job run the ganeti-watcher program. A sample cron file is provided in the source at docs/examples/ganeti.cron and you can copy that (eventually altering the path) to /etc/cron.d/ganeti

3.4. Installing the Operating System support packages

Mandatory on all nodes.

To be able to install instances you need to have an Operating System installation script. An example for Debian Etch is provided on the project web site. Download it from and follow the instructions in the README file. Here is the installation procedure:

cd /srv/ganeti/os
tar xvf instance-debian-etch-0.1.tar
mv instance-debian-etch-0.1 debian-etch

In order to use this OS definition, you need to have internet access from your nodes and have debootstrap(8) installed on all the nodes.

Debian. Use this command on all nodes to install debootstrap:

apt-get install debootstrap

Alternatively, you can create your own OS definitions. See the manpage ganeti-os-interface(8).

3.5. Initializing the cluster

Mandatory: only on one node per cluster.

The last step is to initialize the cluster. After you've repeated the above process on all of your nodes, choose one as the master, and execute:

gnt-cluster init CLUSTERNAME

The CLUSTERNAME is a hostname, which must be resolvable (e.g. it must exist in DNS or in /etc/hosts) by all the nodes in the cluster. You must choose a name different from any of the nodes names for a multi-node cluster. In general the best choice is to have a unique name for a cluster, even if it consists of only one machine, as you will be able to expand it later without any problems.

If the bridge name you are using is not xen-br0, use the -b BRIDGENAME option to specify the bridge name. In this case, you should also use the --master-netdev BRIDGENAME option with the same BRIDGENAME argument.

You can use a different name than xenvg for the volume group (but note that the name must be identical on all nodes). In this case you need to specify it by passing the -g VGNAME option to gnt-cluster init.

You can also invoke the command with the --help option in order to see all the possibilities.

3.6. Joining the nodes to the cluster

Mandatory: for all the other nodes.

After you have initialized your cluster you need to join the other nodes to it. You can do so by executing the following command on the master node:

gnt-node add NODENAME

3.7. Separate replication network


Ganeti uses DRBD to mirror the disk of the virtual instances between nodes. To use a dedicated network interface for this (in order to improve performance or to enhance security) you need to configure an additional interface for each node. Use the -s option with gnt-cluster init and gnt-node add to specify the IP address of this secondary interface to use for each node. Note that if you specified this option at cluster setup time, you must afterwards use it for every node add operation.

3.8. Testing the setup

Execute the gnt-node list command to see all nodes in the cluster:

# gnt-node list
Node              DTotal  DFree MTotal MNode MFree Pinst Sinst 197404 197404   2047  1896   125     0     0

4. Setting up and managing virtual instances

4.1. Setting up virtual instances

This step shows how to setup a virtual instance with either non-mirrored disks (plain) or with network mirrored disks (remote_raid1). All commands need to be executed on the Ganeti master node (the one on which gnt-cluster init was run). Verify that the OS scripts are present on all cluster nodes with gnt-os list.

To create a virtual instance, you need a hostname which is resolvable (DNS or /etc/hosts on all nodes). The following command will create a non-mirrored instance for you:

gnt-instance add --node=node1 -o debian-etch -t plain
* creating instance disks...
adding instance to cluster config
Waiting for instance to sync disks.
Instance's disks are in sync.
creating os for instance on node
* running the instance OS create scripts...

The above instance will have no network interface enabled. You can access it over the virtual console with gnt-instance console inst1. There is no password for root. As this is a Debian instance, you can modify the /etc/network/interfaces file to setup the network interface (eth0 is the name of the interface provided to the instance).

To create a network mirrored instance, change the argument to the -t option from plain to remote_raid1 and specify the node on which the mirror should reside with the --secondary-node option, like this:

# gnt-instance add -t remote_raid1 --secondary-node node1 \
  -n node2 -o debian-etch instance2
* creating instance disks...
adding instance instance2 to cluster config
Waiting for instance instance1 to sync disks.
- device sdb:  3.50% done, 304 estimated seconds remaining
- device sdb: 21.70% done, 270 estimated seconds remaining
- device sdb: 39.80% done, 247 estimated seconds remaining
- device sdb: 58.10% done, 121 estimated seconds remaining
- device sdb: 76.30% done, 72 estimated seconds remaining
- device sdb: 94.80% done, 18 estimated seconds remaining
Instance instance2's disks are in sync.
creating os for instance instance2 on node
* running the instance OS create scripts...
* starting instance...

4.2. Managing virtual instances

All commands need to be executed on the Ganeti master node

To access the console of an instance, use gnt-instance console INSTANCENAME.

To shutdown an instance, use gnt-instance shutdown INSTANCENAME. To startup an instance, use gnt-instance startup INSTANCENAME.

To failover an instance to its secondary node (only possible in remote_raid1 setup), use gnt-instance failover INSTANCENAME.

For more instance and cluster administration details, see the Ganeti administrator's guide.