What is the difference between application server and web server?

Question

What is the difference between application server and web server?

Answer 1

As Rutesh and jmservera pointed out, the distinction is a fuzzy one. Historically, they were different, but through the 90's these two previously distinct categories blended features and effectively merged. At this point is is probably best to imagine that the "App Server" product category is a strict superset of the "web server" category.

Some history. In early days of the Mosaic browser and hyperlinked content, there evolved this thing called a "web server" that served web page content and images over HTTP. Most of the content was static, and the HTTP 1.0 protocol was just a way to ship files around. Quickly the "web server" category evolved to include CGI capability - effectively launching a process on each web request to generate dynamic content. HTTP also matured and the products became more sophisticated, with caching, security, and management features. As the technology matured, we got company-specific Java-based server-side technology from Kiva and NetDynamics, which eventually all merged into JSP. Microsoft added ASP, I think in 1996, to Windows NT 4.0. The static web server had learned some new tricks, so that it was an effective "app server" for many scenarios.

In a parallel category, the app server had evolved and existed for a long time. companies delivered products for Unix like Tuxedo, TopEnd, Encina that were philosophically derived from Mainframe application management and monitoring environments like IMS and CICS. Microsoft's offering was Microsoft Transaction Server (MTS), which later evolved into COM+. Most of these products specified "closed" product-specific communications protocols to interconnect "fat" clients to servers. (For Encina, the comms protocol was DCE RPC; for MTS it was DCOM; etc.) In 1995/96, these traditional app server products began to embed basic HTTP communication capability, at first via gateways. And the lines began to blur.

Web servers got more and more mature with respect to handling higher loads, more concurrency, and better features. App servers delivered more and more HTTP-based communication capability.

At this point the line between "app server" and "web server" is a fuzzy one. But people continue to use the terms differently, as a matter of emphasis. When someone says "web server" you often think HTTP-centric, web UI, oriented apps. When someone says "App server" you may think "heavier loads, enterprise features, transactions and queuing, multi-channel communication (HTTP + more). But often it is the same product that serves both sets of workload requirements.

• WebSphere, IBM's "app server" has its own bundled web server.
• WebLogic, another traditional app server, likewise.
• Windows, which is Microsoft's App Server (in addition to being its File&Print Server, Media Server, etc.), bundles IIS.