This tutorial demonstrates a minimal installation of a StratusLab cloud on two physical machines. Before trying to install the StratusLab software there are many prerequisites that must be satisfied by the hardware, operating system, and software.

Physical Machines

The physical machines should be relatively modern machines with the following minimum characteristics:

  • 1 64-bit multicore CPU (>= 4 cores)
  • 4 GB of RAM
  • 200 GB local disk space

In general cloud infrastructures prefer “fat” machines; that is machines that have the maximum number of CPUs, RAM, and disk space as possible. This is because the maximum size of a single virtual machine is limited by the size of the largest physical machine.

Virtualization Support

The machine must have a CPU that supports the VT-x virtualization extensions and must have this support enabled in the BIOS. Many vendors ship machines with these extensions disabled.

RedHat has a good document for checking if your machine will support virtualization. In short, check the /proc/cpuinfo for the proper flags:

$ grep vmx /proc/cpuinfo

and check the dmesg console for any KVM errors when trying to load the KVM kernel module:

$ dmesg | grep kvm

looking for any messages about KVM not supporting virtualisation or having it disabled in BIOS.

Operating System

Be sure to read all of the operating system requirements before installing your machines. This will save you from having to do the installation multiple times!

Supported Versions

Install a minimal version of CentOS 6 on the two physical machines that will be used for the cloud infrastructure. Other distributions that are compatible with CentOS 6 will likely work; however, only CentOS 6 is systematically tested.

Operating Systems in the Debian family (e.g. Ubuntu) are not currently supported.

Disable SELinux

The SELinux system must be disabled on all of the machines in the cloud infrastructure. The standard CentOS installation procedure normally activates SELinux.

To disable SELinux, ensure that the file /etc/selinux/config has the following line:


You can also use the commands getenforce and sestatus to find the current SELinux status. Changes in this configuration are only taken into account after rebooting the machine.

You can reboot the machine to have your changes taken into account or disable SELinux temporarily:

$ echo 0 > /selinux/enforce

This change will be lost at the next reboot unless you have also changed the /etc/selinux/config configuration file.

Disk Configuration

StratusLab allows for a variety of storage options behind the persistent disk service.

This tutorial uses the default storage solution using LVM and iSCSI. Because of this, the machines must be configured to use LVM for the disk storage.

The Front End will host the storage service and the physical storage associated with it. It is strongly recommended that the Front End machine be configured with two LVM groups: one for the base operating system (~20 GB) and one for the StratusLab storage service (remaining space). One LVM group is possible, but you risk starving normal system services of disk space.

In the tutorial, we assume that the volume group names are “vg.01” for the operating system and “vg.02” for the StratusLab storage service on the Front End. You can use other names, but change the commands and configuration parameters below as necessary.

The “Node” machine can be configured with a single LVM group.

You can see the configured volume groups with the command:

$ vgdisplay

 --- Volume group ---
 VG Name               rootvg
 System ID
 Format                lvm2

You’ll need the volume group name “VG Name” of the volume group you’ll be using for the cloud storage. Verify that the device associated with the group name exists. Here for example, the device is /dev/rootvg.


Python Version

The default version of Python installed with CentOS should be correct. Verify that the correct version of Python is installed:

$ python --version
Python 2.6.6

StratusLab requires a version of Python 2 with a version 2.6 or later. The StratusLab command line tools do not work with Python 3.

Package Repositories

The StratusLab installation takes packages from four yum repositories:

  1. The standard CentOS repository,
  2. The EPEL 6 repository,
  3. The StratusLab repository, and
  4. The IGTF Root Certificates.

The configuration for the CentOS repository is done when the system is installed and the IGTF repository will be configured by the StratusLab tools as necessary. The others require explicit configuration.

The directory /etc/yum.repos.d contains the currently configured yum repositories.

EPEL Repository

Configure both the Front End and Node for the EPEL repository. Do the following:

$ wget -nd
$ yum install -y epel-release-6-8.noarch.rpm

This will add the necessary files to the /etc/yum.repos.d/ directory. You can find the latest version of the EPEL configuration RPM on the EPEL wiki.

StratusLab Repository

To configure both the Front End and Node for the StratusLab repository, put the following into the file /etc/yum.repos.d/stratuslab.repo:


replacing the URL with the version you want to install.

Cleanup and Upgrade

Although not strictly necessary, it is advisable to clear all of the yum caches and upgrade the packages to the latest versions:

$ yum clean all
$ yum upgrade -y

This may take some time if you installed the base operating system from old media.

Network Setup

DNS and Hostname

Ensure that the hostname is properly setup on the Front End and the Node. The DNS must provide both the forward and reverse naming of the nodes. For example:

$ host is an alias for has address

$ host domain name pointer

Ensure that the host resolves to an IP address and that the IP address resolves back to the original name (or alias).

Also ensure that the hostname is properly set for the node:

$ hostname -f

should return the full hostname (with domain). Set the hostname if it is not correct.

Throughout this tutorial we use the variables $FRONTEND_HOST ($FRONTEND_IP) and $NODE_HOST ($NODE_IP) for the Front End and Node hostnames (IP addresses), respectively. Change these to the proper names for your physical machines when running the commands.

DHCP Server

You must have a range of free IP addresses that can be assigned to virtual machines. The range should be large enough to handle the maximum number of virtual machines you expect to have running simultaneously on your infrastructure.

These IP addresses must be publicly visible if the cloud instances are to be accessible from the internet.

In addition, a DHCP server must be configured to assign static IP addresses corresponding to known MAC addresses for the virtual machines. You can use an external DHCP server or if one is not available (or not desired), the StratusLab installation command can be used to properly configure a DHCP server on the Front End for the virtual machines.

This tutorial will start a DHCP server on the Front End by default.

Network Bridge

A network bridge must be configured on the Node to allow virtual machines access to the internet. You can do this manually if you want, but the StratusLab installation scripts are capable of configuring this automatically.

This tutorial uses the installation scripts to configure the network bridge.

SSH Configuration

The installation scripts will automate most of the work, but the scripts require password-less root access:

  • From the Front End to each Node and
  • From the Front End to the Front End itself

Check to see if there is already an SSH key pair in /root/.ssh/id_rsa*. If not, then you need to create a new key pair without a password:

$ ssh-keygen -q
Enter file in which to save the key (/root/.ssh/id_rsa):
/root/.ssh/id_rsa already exists.
Overwrite (y/n)? y
Enter passphrase (empty for no passphrase):
Enter same passphrase again:

Now do the necessary configuration to ensure that you can log into the Front End from the Front End with your SSH key (and without a password). Do the following:

$ ssh-copy-id $FRONTEND_HOST
The authenticity of host ' (' can't be established.
RSA key fingerprint is e9:04:03:02:e5:2e:f9:a1:0e:ae:9f:9f:e4:3f:70:dd.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added ',' (RSA) to the list of known hosts.'s password:
Now try logging into the machine, with "ssh ''", and check in:


to make sure we haven't added extra keys that you weren't

and then the same thing for the node:

$ ssh-copy-id $NODE_HOST

After these commands you key should have been added to the authorized_key file on both nodes and should allow you to log in without a password.


If you machine does not have the ssh-copy-id command, then you will have to do the configuration by hand. Append the contents of your $HOME/.ssh/ file to the $HOME/.ssh/authorized_keys file on both the Front End and the Node. You will also have to accept the host’s SSH key the first time you log in.

Verify that the password-less access works as expected.


Last login: Mon May 27 14:26:29 2013 from
# exit
Connection to closed.

$ ssh $NODE_HOST

Last login: Mon May 27 14:26:43 2013 from
# exit
Connection to closed.

Now that SSH is properly configured, the StratusLab scripts will be able to install software on both the Front End and the Node.