Application servers consist of server OSes and server hardwares that work together to provide computing-intensive operations and services to the residing application. The application servers execute and provide user other app access when utilizing the installed application's business/functional logic. Key required features of an application server include data redundancy, database access, high availability, load balancing, user management, data/application security, centralized management interface, and so on.
In the field of web, an application server runs behind a web server (such as Apache, Nginx, or Microsoft IIS) and in front of database servers (such as MySQL, Oracle, or SQL Server). There are many application servers and the choice impacts the cost, performance, reliability, scalability, and maintainability of an application.
How It Works
Application server can be used as a processor, especially for business logic. An application server is generally described a three tier application. The three levels are Graphical User Interface (GUI), application server, and a database server. The GUI acts as the front end of the application, while business logic applications work in the middle tier on a local area network. At the back end is the database or transaction server. Sometimes application servers work with the web using Hyper Text Transfer Protocol (HTTP) and are known as web application servers.