By: IBM Cloud Education

Learn how web servers and application servers are different, how they’re the same, and how they combine to deliver most of the applications you use today.

Web server vs. application server: What is the difference?

By strict definition, a web server is a common subset of an application server.

A web server delivers static web content—e.g., HTML pages, files, images, video—primarily in response to hypertext transfer protocol (HTTP) requests from a web browser.

An application server typically can deliver web content too, but its primary job is to enable interaction between end-user clients and server-side application code—the code representing what is often called business logic—to generate and deliver dynamic content, such as transaction results, decision support, or real-time analytics. The client for an application server can be the application’s own end-user UI, a web browser, or a mobile app, and the client-server interaction can occur via any number of communication protocols.

In practice, however, the line between web servers and application servers has become fuzzier, particularly as the web browser has emerged as the application client of choice and as user expectations of web applications and web application performance have grown.

Most web servers support plug-ins for scripting languages (e.g., ASP, JSP, PHP, Perl) that enable the web server to generate dynamic content based on server-side logic. And an increasing number of application servers not only incorporate web server capabilities, but use HTTP as their primary protocol and support other protocols (e.g., CGI and CGI variants) for interfacing with web servers. They also allow web applications to leverage services like reverse proxy, clustering, redundancy, and load balancing—services that improve performance and reliability and allow developers to focus less on infrastructure and more on coding.

To make matters more confusing, many web servers and some application servers are referred to, or refer to themselves, as web application servers.

The bottom line is that today’s most popular web servers and application servers are hybrids of both. Most of the increasingly rich applications you use today feature a combination of static web content and dynamic application content, delivered via a combination of web server and application server technologies.

Open source web servers and application servers

The market is flooded with web servers and application servers—too many to list here. Instead, we thought it might be more valuable to list the most popular free, open source options available:

Nginx

Nginx is an open source web server that includes reverse proxy, load balancing, mail proxy, and HTTP cache capabilities. (Commercial, supported versions of Nginx are also available, at Nginx, Inc.) According to the internet research and cybercrime prevention company Netcraft, Nginx served or proxied nearly 38% of all the world’s websites and over 25% of the million busiest sites as of December, 2019. World-known enterprise Nginx users include Dropbox, Netflix, and Zynga.

Apache HTTP Server

First released in 1995, Apache HTTP Server (also just known as ‘Apache’) is another very popular free, open source web server that, until very recently, powered more websites than any other web server—71% at its peak—before being overtaken by Nginx in April, 2019. As of December 2019, Apache served over 24% of all sites worldwide and 31% of the million busiest sites.

Apache Tomcat

Apache Tomcat is an open source application server that executes Java Servlets, renders and delivers web pages that include JavaServer Page code, and serves Java Enterprise Edition (Java EE) applications. Released in 1998, Tomcat is the most widely used open source Java application server.

Glassfish

Glassfish is an open source Java EE application server launched by Sun Microsystems in 2006, and it is hosted today by the Eclipse Foundation. Like most Java application servers, Glassfish supports Java Servlets, Enterprise JavaBeans (EJB), and more, but it can also function as a web server, serving up web content in response to HTTP requests.

Web servers, application servers, and IBM Cloud

IBM offers HTTP Server, a web server included with other products such as IBM WebSphere Application Server. IBM HTTP Server is based on the Apache HTTP Server and provides all Apache features, plus IBM enhancements. Find out more about IBM HTTP Server Powered by Apache, Version 9.0.

IBM WebSphere Liberty is a Java EE application server designed for cloud native applications and microservices. WebSphere Liberty is built on the Open Liberty project that provides an open source Java EE and MicroProfile core. Read about the results of one company’s transition to IBM’s WebSphere Application Server Liberty Profile on the IBM Cloud Private platform.

For more information on web servers and application servers or to get started today, sign up for your IBMid and create your IBM Cloud account.