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3.4 Fail over servers


One key feature of a virtual server is the independence from the actual hardware. Most hardware issues are irrelevant for the virtual server installation. For example:

  • Disk layout, partitions and the /etc/fstab configuration. The virtual server has a dummy /etc/fstab.
  • Network devices.
  • Processor type, number of processor (kernel selection).

The main server acts as a host and takes care of all those details. The virtual server is just a client and ignores all the details. As such, the client can be moved to another physical server will very few manipulations. For example, to move the virtual server v1 from one physical one computer to another, you do

  • Turn it off
    /usr/sbin/vserver v1 stop
  • Copy the file /etc/vservers/v1.conf to the new server.
  • Copy all files in /vservers/v1 to the new server
  • On the new server, start the vserver v1
    /usr/sbin/vserver v1 start

As you see, there is no adjustment to do:

  • No user account merging.
  • No hardware configuration to fix.

This opens the door to fail over servers. Imagine a backup server having a copy of many virtual servers. It can take over their tasks with a single command. Various options exists for managing this backup server:

  • rsync to synchronize the data.
  • Network block devices to synchronize the data in real time.
  • Sharing the installation over a SAN (storage area network).
  • Heartbeat for automatic monitoring/fail over.
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