An application server is a server that hosts applications or software that delivers a business application through a communication protocol. For a typical web application, the application server sits behind the web servers. An application server framework is a service layer model. It includes software components available to a software developer through an application programming interface. An application server may have features such as clustering, fail-over, and load-balancing. The goal is for developers to focus on the business logic.

Java application servers

Jakarta EE (formerly Java EE or J2EE) defines the core set of API and features of Java application servers. The Jakarta EE infrastructure is partitioned into logical containers.

Microsoft

Microsoft's .NET positions their middle-tier applications and services infrastructure in the Windows Server operating system and the .NET Framework technologies in the role of an application server. The Windows Application Server role includes Internet Information Services (IIS) to provide web server support, the .NET Framework to provide application support, ASP.NET to provide server side scripting, COM+ for application component communication, Message Queuing for multithreaded processing, and the Windows Communication Foundation (WCF) for application communication.

PHP application servers

PHP application servers run and manage PHP applications.

Third-party

Mobile application servers

Mobile application servers provide data delivery to mobile devices.

Mobile features

Core capabilities of mobile application services include

Mobile challenges

Although most standards-based infrastructure (including SOAs) are designed to connect to any independent of any vendor, product or technology, most enterprises have trouble connecting back-end systems to mobile applications, because mobile devices add the following technological challenges:

Deployment models

An application server can be deployed: