Software appliance

A software appliance is a software application that might be combined with just enough operating system (JeOS) for it to run optimally on industry standard hardware (typically a server) or in a virtual machine.

Virtual appliances are a subset of software appliances. The main distinction is the packaging format and the specificity of the target platform. A virtual appliance image is designed to run on a specific virtualization platform, while a software appliance is often packaged in more generally applicable image format (e.g., Live CD) that supports installations to physical machines and multiple types of virtual machines.

Installing a software appliance to a virtual machine and packaging that, creates a virtual appliance.

Benefits

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.

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.

There is currently no standard virtual machine container format, so a virtual appliance is usually built specifically for a single type of virtual machine and will not run on other virtual machines type.

Live CD appliance

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 (i.e., ISO images are supported by most Virtual Machine platforms).

Commercial software appliances

Commercial software appliances are typically sold as a subscription service (pay-as-you-go) 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.

See also

• JeOS
• Virtual appliance
• Virtual machine
• Portable application
• TurnKey Linux Virtual Appliance Library
• VMware ThinApp