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The primary goal of this project is to create virtual servers sharing the same machine. A virtual server operates like a normal Linux server. It runs normal services such as telnet, mail servers, web servers, and SQL servers.
This allows a clever provider to sell something called Virtual Private Server, which uses less resources than other virtualization techniques, which in turn allows to put more units on a single machine.
The list of providers doing so is relatively long, and so this is rightfully considered the main area of application.
Separating different or similar services which otherwise would interfere with each other, either because they are poorly designed or because they are simply incapable of peaceful coexistence for whatever reason, can be easily done with Linux-VServer.
But even on the old-fashioned real server machines, putting some extremely exposed or untrusted, because unknown or proprietary, services into some kind of jail can improve maintainability and security a lot.
While it can be interesting to run several virtual servers in one box, there is one concept potentially more generally useful. Imagine a physical server running a single virtual server. The goal is isolate the main environment from any service, any network. You boot in the main environment, start very few services and then continue in the virtual server.
The service in the main environment would be:
Another option is to put the firewall in a virtual server, and pull in the DMZ, containing each service in a separate VPS. On proper configuration, this setup can reduce the number of required machines drastically, without impacting performance.
One key feature of a virtual server is the independence from the actual hardware. Most hardware issues are irrelevant for a virtual server installation.
The main server acts as a host and takes care of all the details. The virtual server is just a client and ignores all the details. As such, the client can be moved to another physical server with very few manipulations.
For example, to move the virtual server from one physical computer to another, it sufficient to do the following:
No adjustments to user setup, password database or hardware configuration are required, as long as both machines are binary compatible.
Pushing the limit a little further, replication technology could be used to keep an up-to-the-minute copy of the filesystem of a running Virtual Server. This would permit a very fast fail-over if the running server goes offline for whatever reason.
All the known methods to accomplish this, starting with network replication via rsync, or drbd, via network devices, or shared disk arrays, to distributed filesystems, can be utilized to reduce the down-time and improve overall efficiency.
Consider a software tool or package which should be built for several versions of a specific distribution (Mandrake 8.2, 9.0, 9.1, 9.2, 10.0) or even for different distributions.
This is easily solved with Linux-VServer. Given plenty of disk space, the different distributions can be installed and running side by side, simplifying the task of switching from one to another.
Of course this can be accomplished by chroot() alone, but with Linux-VServer it's a much more realistic simulation.