Pattern - Machine Cloning

Features

• Physical Machines are cloned using commercial cloning tools.
• Virtual Machines can be cloned by copying the files containing the disk images.
• With Virtualisation, the cloned machines can have a lifespan of a few minutes to a few hours.
• It is possible to take a physical machine and clone it to an image that is hosted in a Virtual Machine.

Advantages

• Takes a system in any state and scales it up to support more than one machine.
• Can be fully automated.
• Short-lived virtual machines can be brought up for a short period, and destroyed afterwards.
• Can take a functional system whose actual state/configuration is unknown, and allows developers to have a development image.
• Can be used.

Disadvantages

• Windows does not like domained machines being duplicated, unless the machine ID is changed. The new machine needs to be redomained by an authorised domain administrator.
• Requires target hardware to match that of the source system, otherwise migration effort/costs are higher.
• Long-lived machine clones will diverge in configuration/state. If the machines are manually managed, this increases costs.

On one project, [Steve Loughran] had an entertaining crisis as a test system was being brought up based on a clone of a production site. Although the machine had cloned, the database stayed bonded to the production machine. The specific version of SQL Server used required a unique name for the database across the entire private intranet. When the test machine was brought up and the database purged of sensitive data, it took out the production site instead. Fortunately, there was a backup.