Welcome to the virtual world!
For some reason, I feel that I should leave the definitions to wikipedia and only quote it so that is what I am going to do:
Virtualization (of software and hardware platforms) is really nothing new and has been around since..well the the real thing itself: computers. There has been several implementations of different kind ever since and I are two main reason they exist and grow:
- Developing/testing software for hardware that you do not have. This makes virtualization softwares were attractive for consumer product manufacturers to be able to start the development of software soon after the plans for a particular product are finalized since it takes some time before they can manufacture enough prototypes for every developer and tester involved.
- Portability: In a typically VM setup, installation is done on drive images (files) rather than actual drives/partitions, which means you can carry or send your (virtual) machine anywhere you like.
- Ability to use multiple operating systems at the same time: Many Linux and Mac OS X users often need to run applications that are only available for windows and vice versa. Dual-boot is one solution to this issue but that implies you will only be able to use one OS at a time.
- Partitioning of a single host to multiple servers: Consolidation of many servers to a single host is a popular use case these days, done internally in many companies and also by hosting services. aka “The Cloud”.
There are many such solutions out there, both Free and non-Free out there but the solution of our choice is Qemu. This awesome virtual-machine manager (a.k.a hypervisor) combined with Kernel-based Virtual Machine (KVM) and built-in virtualization extensions in modern CPUs is capable of providing such a virtual environment that puts the real thing to shame.
Qemu+kvm might be a very powerful tool, its still very much a power-user tool. For example you have to use long commandlines with different switches to use Qemu effectively . Worry not! There is another set of tools to help there:
While Qemu+KVM might be an awesome solution, its still one of the many hypervisors out there and with some many people pouring into the virtualization industry, you can be assured that there will be a better alternative available sooner or later. libvirt not only abstracts you from hypervisors but also adds some really nice features on top of that:
- Manipulation (creation, deletion and modification etc) and monitoring etc of virtual machines on remote hosts, securely.
- Live migration of virtual machine(s) from one host to another.
Neither libvirt, not virsh are tools that an end-user could be expected to use. Thats where virt-manager comes into picture. It basically provides the same functionality as virsh but unlike virsh, its designed for end-users and hence has a very user-friendly graphical user-interface. Here is some screenshots that should give you a good idea:
SPICE in simple words can be described as very smart remote-access enabler for virtual machines. Oh wait, I was supposed to leave definitions to wikipedia:
SPICE was originally developed by Qumranet as a proprietary solution. Red Hat acquired Qumranet in 2008 and in December 2009 Red Hat open-sourced the protocol.
Now with definition and history lesson taken care of, lets talk about the real thing: tools. SPICE, the implementation is divided into 3 main parts:
This is the tool that end-user should be concerned with. It provides a view into the guest OS (very much like the popular VNC).In the past there was only one SPICE client called, spicec. Due to various reasons (not embeddable, too low-level etc), it was deemed necessary to create a better client-tool. So for the past some months, our team has been working on a SPICE client Gtk+ widget called (surprise suprice) spice-gtk and helped in integration of it in vinagre (the GNOME remote-desktop client). I still haven’t used (or even built) spicec but from what I’ve been told, vinagre+spice-gtk are already much better than spicec in functionality so I guess I haven’t missed anything. Wait! Why am I telling you all this when I can just show you?
There are certain important tasks that spice-server needs to perform that it can not do so itself as it runs on the host rather than guest. A good example is copy/cut and paste between client’s host and guest desktop. For this reason, vdagent exists. Its a helper that runs inside the guest (and as such is installed from the guest). So making the copy&paste possible, it proxies the appropriate events to/from the SPICE client from/to guest windowing system through spice-server.
Whats wrong with VNC?
VNC has been around for a while now and in modern unix world, its considered as the remote desktop solution so its natural for people to ask: why create yet another solution for the same problem? The reason is that SPICE protocol has been designed to be very efficient on bandwidth usage and to satisfy the needs of a virtualized environment  . Recall QXL I mentioned above? QXL is handled/implemented as something called paravirtual devices in SPICE. Its probably appropriate to quote the related wikipedia definition here first:
I am really not good at explaining things so I’m sure I must have left-out some necessary details but worry not! We have a team of awesome hackers who can always help you with any issues related to SPICE. You can reach us either through our IRC channel or mailing-list . If you are attending the Desktop Summit 2011 in Berlin, you are in luck cause not only there is a talk about ‘Integrating virtualization into the desktop’ but also some of us will be attending the full duration of the conference so you can come and discuss with us in person.