With the free Citrix XenServer 5.5 software, solutions providers can create a virtual environment in which virtual machines (VMs) are assigned to the host where needed. If a host goes down unexpectedly, nothing will happen to the VMs that were running on it. If a customer needs automatic failover, then they also need XenServer high availability. In this article, you'll learn how to set up Citrix XenServer 5.5 high availability.
To use high availability, your customers need Citrix Essentials. Citrix Essentials has to be purchased, but it gives you lots of useful tools, including services for automatically provisioning VMs. If you want to check out the software first, you can download a free 30-day version of Citrix Essentials.
After downloading the ISO file, you need to write it to a CD. From there, you can start the Citrix Essentials installation program. You must run the installation on the same workstation as the one in which your XenCenter console is installed.
Before starting the installation, make sure that Microsoft SQL Server and the Microsoft SQL Server 2005 backward compatibility components are installed on the target computer. You can download this software for free from Microsoft's website. After installing these components, make sure a base database is created and that you can access this database as a user who is a member of the SQL Administrators group. Once you've verified this, you can start the installation program for XenServer high availability.
After you begin installing the Citrix Essentials software, from the main program interface, click the Workload Balancing option. The name may actually surprise you, but Citrix Workload Balancing is just the name that is used within the software to refer to XenServer high availability. Be sure you select the workload balancing services and data store for installation, connect to the SQL database and, when prompted later, select Install a new Workload Balancing Data Store.
Next, you must specify the settings for Citrix XenServer 5.5 communications. To do this, first provide a group name for the account for the Web service host. XenServer uses this account to connect to workload balancing. After specifying which account you will use for this purpose, select the certificate you want to use to set up a secure connection between the Citrix XenServer 5.5 environment and the Web environment. In case you don't have an existing certificate coming from your customer's Certificate Authority, you can choose to create a self-signed certificate.
Using Citrix XenServer 5.5 high availability
Before you can start using XenServer high availability, you need to activate it. To do that, connect to the licensing server or just add the license from XenCenter. To do the latter, from XenCenter, open the Server menu and select Install License Key. Browse to the license file that you downloaded earlier and add it to XenCenter. Repeat this procedure for each of the high-availability servers that you want to use.
At this point, you can start the XenServer high-availability wizard to configure your customer's environment. You can select this option from the Pool > High Availability option. To set up high availability, it is important that the virtual disk storage is on an iSCSI or Fibre Channel storage area network (Figure 1).
Figure 1 -- For your customer's virtual machines to work with XenServer high availability, they need a storage area network.
In the first step of the setup wizard, you'll see an overview of all of the available storage. From there, you can select the storage that you want to use in the high-availability environment. Next, from the high-availability protection levels menu, select the virtual machines that you want to protect. Make sure that "Protect" is selected for all of the VMs, which adds the highest protection level to your servers (Figure 2). After this step is complete, you will have finished the wizard and added high availability to the selected VMs. Your customer's VMs are now protected and will even survive a power failure on their network!
Figure 2 -- Select Protect to add the highest level of protection to your servers.
Setting up high availability in a Citrix XenServer 5.5 environment is not easy, as many components are involved. However, once you've got the basic product installed, you'll see that actually protecting the VMs is not that hard. Just enable protection and, after a power failure, your customer's VM will restart.
About the expert
Sander van Vugt is an independent trainer and consultant living in the Netherlands. Van Vugt is an expert in Linux high availability, virtualization and performance and has completed several projects that implement all three. He is also the writer of various Linux-related books, such as Beginning the Linux Command Line, Beginning Ubuntu Server Administration and Pro Ubuntu Server Administration.