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A ceux qui ne savent toujours pas ce qu'est le projet vserver: Il vous permet de lancer Linux dans Linux: autant de distributions que vous le souhaitez à l'intérieur de n'importe quelle autre. Chaque serveur virtuel a ses propres packages, ses propres services, ces propres utilisateurs et est confiné pour n'utiliser que certaines adresses IP et certaines parties du système de fichier. Vous pouvez les considérer comme des machines virtuelles.

Aux yeux de certains, vserver ressemble peut etre a un tres beau jouet: Excellent pour les geek, tres sympa, mais sans doute pas pour tout le monde. Faux!

Quelques specifications et explications

1-Un ensemble de vservers travaillent a l'aide un seul et meme noyau, celui de l'hote. Les performances sont exactement identiques a celles d'un hote traditionnel. (contrairement aux autres solutions a base de Machines Virtuelles (VM) ).

2-Les vserver n'engendrent pas de cout de traitement supplementaire. Aucun demon ne tourne. Un vserver fait tourner par exemple crond, sshd, httpd et utilise les memes ressources qu'un serveur linux traditionnel.

3-Les vserver partagent en general le meme espace disque que la machine hote, il n'y a donc aucun besoin d'allouer de l'espace a chacun d'entre eux, pour s'apercevoir ensuite que votre disque est plein. Chaque vserver utilise la portion d'espace qui lui est alloue.

4-Un vserver supplementaire coute seulement 40 a 100Mo d'espace disque supplementaire. Il partage les binaires et les bibliotheques du premier vserver. Une grande partie de l'espace occupe est constitue par la copie de la base de paquets RPM.

5-Les vservers sont mis a jour independemment meme s'ils partagent leurs binaires avec d'autres vservers.

6-Les vservers sur distributions 32bits tournent normalement sur un hote en 64bits, parfois plus rapidement, voire meme extremement.

7-Vous pouvez melanger plusieurs distributions de linux sur un meme serveur hote, et les faire fonctionner en parallele. http://www.solucorp.qc.ca est un serveur rh7.3 tournant dans un hote rh7.3 . Nous avons aussi des vserver en FC3, tout autant que des Debian sur la meme machine physique (Pour info, ce n'est qu'un Celeron 500MHz).

8- Vos outils d'administration tournent dans un vserver tout a fait comme d'habitude.

9-A cracked vserver can't reach the host server. The host server may be used to safely investigate the cracked server (and fix it), something almost impossible with a typical linux installation.

Why do you need vservers ?

Believe me this will change a lot, but once you figure it out you will never look back. Here are some ideas

A) Many tasks on the same box

As the hardware evolves, it is tempting to put more and more tasks on a server. Linux can handle it. Linux is reliable and so on. At some point, you end up with so much stuff and so much people fiddling in the same box that you worry about updating things.

Vservers address this. The same box runs multiple vservers and each one does the job it is supposed to do. If you need to upgrade to php5 for a given project you do so and only this project is affected.

Also, you can give the root password of a vserver to one administrator and he will be able to perform updates, restart services and so on without having to know about every other project hosted on a server.

b) Moving vserver around

Once you have found that a project is using more resource than expected, you can move it to another box without having to fiddle here and there. A vserver is just a directory inside the host server. You tar it and copy it to another box and restart it there.

An administrator can move vservers around without knowing what they do.

c) Experimenting and upgrading.

You have this typical problem. You intend to upgrade a site either with new package (new PHP5) or new features (new version of the Web applications). After having tested all this on the development machine, you are ready to update the production server. Having some experience you do it properly

  • First a good backup of the server
  • Then you perform all the upgrades and install the new applications
  • Fire: the new server is online and kicking.
  • 2 hours later, you realise that something does not work as expected.
  • To make it worse, it works fine on the development machine.
  • Now it is 2 am and this has to work by 8am. Hum. (A famous french song: Je m'arrete ou je continue) Should I stop and restore the tape or hang on and hope to find the problem...

We have all experienced this. Another solution to this problem would be to install the new production server on new hardware, but this is not as easy, as you have to clone the first server (most people are not confortable doing this) or you do not have the hardware.

Using vserver, all this is very easy

  • You stop the production vserver
  • You clone it (Cloning a vserver takes 1 minute unless it has a lot of data).
  • You perform the upgrades in the new vserver and give it life.

Later you find it does not work as expected and you can't immediately fix it.

  • You turn off the new vserver and assign it a new IP number.
  • You start both the old and new. Now the old is still online and you can fiddle with the new (on a different IP address) to fix the problem.

d) development

You are working on a new project. At this point you have no idea of the resources it will need (load). In general, you have a meeting and make a decision about the new hardware. But in this case we have no idea. So instead, we put the new project on a vserver on the first available linux box, including the workstation of the developer. And we develop. Once the thing is ready, we clone the vserver on some production server and give it a go.

Later once we know how popular the new service is, we can move it again to a more powerful server, as needed, without any fiddling (moving accounts, installing packages, and so on)

On my notebook, I have 33 vservers allowing me to tests various project and various distributions from rh6.2 to FC3 and Debian.

We are often talking about our preferred distribution. Should we use FC, Debian or something else ? Should we give a spin to the latest and greatest ?

With vservers, the choice of a distribution is less important. When you select a distribution, you expect it will do the following

  • Good hardware support/detection
  • Good package technology/updates
  • Good package selection
  • Reliable packages

The choice is important because every service running on a box will be using the same distribution. Most distributions out there are good and reliable. But they have flaw. For example, a distribution say XXX is great but is not delivering the latest and greatest PHP. Now because you have decided to use XXX for some projects, it does not prevent you from using XXY for other projects. So instead of moving to XXY for everything, you move to it as you see fit, project per project.

Takes few hours to investigate vservers, you will never look back.