Software appliances have several benefits over traditional software applications that are installed on top of an operating system:
Simplified deployment: A software appliance encapsulates an application's dependencies in a pre-integrated, self-contained unit. This can dramatically simplify software deployment by freeing users from having to worry about resolving potentially complex OS compatibility issues, library dependencies or undesirable interactions with other applications. This is known as a "toaster."
Improved isolation: software appliances are typically used to run applications in isolation from one another. If the security of an appliance is compromised, or if the appliance crashes, other isolated appliances will not be affected.
Improved performance: A software appliance does not embed any unused operating system services, applications or any form of bloatware hence it does not have to share the hardware resources usually consumed by these on a generic OS setup. This naturally leads to faster boot time and application execution speed. In the case where multiple software appliances share and run simultaneously on the same hardware this will not hold true as running n instances of a software appliance will consume more hardware resources than running n instances of a software application on 1 instance of an operating system due to the overhead of running n - 1 more instances of operating system.
Types of software appliances
Virtual appliance
A software appliance can be packaged in a virtual machine format as a virtual appliance, allowing it to be run within a virtual machine container. A virtual appliance could be built using either a standard virtual machine format such as Open Virtualization Format, or a format specific to a particular virtual machine container.
A software appliance can be packaged as a Live CD image, allowing it to run on real hardware in addition to most types of virtual machines. This allows developers to avoid the complexities involved in supporting multiple incompatible virtual machine image formats and focus on the lowest common denominator instead.
Commercial software appliances are typically sold as a subscription service and are an alternative approach to software as a service. Customers can receive all service and maintenance from the application vendor, eliminating the requirement to manage multiple maintenance streams, licenses, and service contracts. In some cases, the application vendor may install the software appliance on a piece of hardware prior to delivery to the customer, thereby creating a computer appliance. In both cases, the primary value to the customer remains the simplicity of purchase, deployment, and maintenance.
