Chapter 2. Core Architecture and Critical Components
In Chapter 1, we stated that “XenServer is a pre-packaged, Xen-based virtualization solution.” This implies that anyone with sufficient skill can re-create XenServer by starting with the Xen hypervisor. In reality, there is a rather large number of decisions anyone embarking on this task must make, and thankfully the team at Citrix has already made the bulk of those decisions. In this chapter, we’ll cover the core components that make up a production XenServer deployment.
XenServer Isn’t Linux, but dom0 Is
The misconception that XenServer is Linux is easily arrived at because from installation to privileged user space access, everything looks, feels, and tools much like a standard Linux environment. The boot loader used is
extlinux, and the installer uses a familiar dialog for interactive setup and post installation. The administrator ends up within a Linux operating system logged in as the privileged user named root.
Post installation, when the Xen hypervisor starts, it is instantiating a privileged VM known as the control domain or, as it is commonly referred to, dom0. This control domain is a Linux VM with a custom kernel and a modified CentOS base with a very small footprint. From an administrative point of view, dom0 can be seen as a true, highly privileged VM that is responsible for core operations within Xen-based virtualization.