An immutable image, as its name implies, does not permanently record changes: changes are available only while the machine is running. As soon as it’s power cycled, changes are lost and the image its reverted to its original state. As in the case of snapshots, VirtualBox will use a differencing image to record changes to an immutable image. The differencing image is then reset to its original state at guest power cycle. The auto-reset feature of a differencing disk can also be turned off. Immutable images can be attached to as many running hosts as you wish: each guest they’ll be attached to will create a new differencing image to store their changes.
Using immutable images with differencing disks is one of the quickest way to deploy multiple instances of the “same” virtual machine. Since more than one virtual machine will be sharing the same underlying image you’ll also spare a good amount of storage space and use it as a way to reduce software installation and licensing for multiple users.
Creating A Virtual Machine
- Create a virtual machine (with a normal image).
- Installe the operating system.
- Finish to configure the environment with most of the configurations all instances would share.
Marking the Image as Immutable
Attaching the Immutable Image to a Virtual Machine
Setting an Image Auto Reset Flag to Off