I have had a few questions recently regarding the benefits of Layering and Application Virtualisation, so I have summarised the basic concept here.
The difference between application layering and application virtualisation, is that layering technology uses a virtual disk to form either a VHD or a VMDK. Once the disk has been created, the application is installed and configured and then the Layer is finalised. The layer is then mapped to an Operating System. The layer can be attached or removed from the operating system without effecting the operating system.
Application Virtualisation is where applications are isolated in their own container which includes virtual filesystem and registry and other components like dll’s etc. Isolating the applications means that they are not allowed to communicate with each other. There are a few methods, one being what we call ached mode where the package is storage on the localhost (local device) or using streaming technology from a central server.
Like with Application virtualisation solutions, the application install is only necessary during the creation process of the layer and only needs to be done once. Updates can be completed on the application layer its self without effecting other applications or the operating system. You would do this by creating versions so existing users are not effected when patching and upgraded are carried out. You can still use application virtualisation with layering and there are some instances with legacy software / bespoke software when application virtualisation still applies. Application management, resource cost and ease of use are some of the reason why I use layering. I have seen issues with layering when using the same application but different versions. For example Outlook 10/13, the mail profile can be corrupted which causes both versions to not work on the final user image.
The figure below shows how the applications and personal apps and data is separated from the Operating System.
Application layers can be stored in different formats and the hypervisor will dictate. Microsoft Hyper-v would create VHD layers and VMware would create VMDK’s naturally.
Stay tuned for a few of my up and coming blog posts on Layering with Microsoft RDS.
Ryan Mangan's IT Blog 
Leave a Reply