Improving Virtual Appliance Management through Virtual Layered File Systems.

Managing many computers is difficult. Recent virtualization trends exacerbate this problem by making it easy to create and deploy multiple virtual appliances per physical machine, each of which can be configured with different applications and utilities. This results in a huge scaling problem for large organizations as management overhead grows linearly with the number of appliances. To address this problem, we introduce Strata, a system that combines unioning file system and package management semantics to enable more efficient creation, provisioning and management of virtual appliances. Unlike traditional systems that depend on monolithic file systems, Strata uses a collection of individual sotware layers that are composed together into the Virtual Layered File System (VLFS) to provide the traditional file system view. Individual layers are maintained in a central repository and shared across all file systems that use them. Layer changes and upgrades only need to be done once in the repository and are then automatically propagated to all virtual appliances, resulting in management overhead independent of the number of appliances. Our Strata Linux prototype requires only a single loadable kernel module providing the VLFS support and doesn't require any application or source code level kernel modifications. Using this prototype, we demonstrate how Strata enables fast system provisioning, simplifies system maintenance and upgrades, speeds system recovery from security exploits, and incurs only modest performance overhead.