What is the difference between application server and web server?

Most of the times these terms Web Server and Application server are used interchangeably.

Following are some of the key differences in features of Web Server and Application Server:

• Web Server is designed to serve HTTP Content. App Server can also serve HTTP Content but is not limited to just HTTP. It can be provided other protocol support such as RMI/RPC
• Web Server is mostly designed to serve static content, though most Web Servers have plugins to support scripting languages like Perl, PHP, ASP, JSP etc. through which these servers can generate dynamic HTTP content.
• Most of the application servers have Web Server as integral part of them, that means App Server can do whatever Web Server is capable of. Additionally App Server have components and features to support Application level services such as Connection Pooling, Object Pooling, Transaction Support, Messaging services etc.
• As web servers are well suited for static content and app servers for dynamic content, most of the production environments have web server acting as reverse proxy to app server. That means while servicing a page request, static contents (such as images/Static HTML) are served by web server that interprets the request. Using some kind of filtering technique (mostly extension of requested resource) web server identifies dynamic content request and transparently forwards to app server

Example of such configuration is Apache Tomcat HTTP Server and Oracle (formerly BEA) WebLogic Server. Apache Tomcat HTTP Server is Web Server and Oracle WebLogic is Application Server.

In some cases the servers are tightly integrated such as IIS and .NET Runtime. IIS is web server. When equipped with .NET runtime environment, IIS is capable of providing application services.

• JBoss(now WildFly) too is a renowned example of Application server :D - KNU
• Glass Fish too. - Revanth Kumar
• Nice explanation, since we can use application server instead of web server what are the advantages of having a web server and application server both for a single application? And performance wise what is the best option? - Lalinda Sampath
• "Apache Tomcat HTTP Server is Web Server and Oracle WebLogic is Application Server." So first of all, Apache Tomcat and Apache HTTP server are 2 different products. And that's not really an accurate statement. Apache Tomcat is an application server. Sure, it can serve web pages as well, but it's an application server for deploying Java. I realize a lot use the term "web server" loosely. But it just confuses people. - ironarm
• Apache Tomcat is not a web server, it is an application server that runs Java servelets. Apache HTTP server is a web server. There is no server called Apache Tomcat HTTP server. - Abhishek Pathak

Both terms are very generic, one containing the other one and vice versa in some cases.

• Web server: serves content to the web using http protocol.

• Application server: hosts and exposes business logic and processes.

I think that the main point is that the web server exposes everything through the http protocol, while the application server is not restricted to it.

That said, in many scenarios you will find that the web server is being used to create the front-end of the application server, that is, it exposes a set of web pages that allow the user to interact with the business rules found into the application server.

This is a detailed answer with some scenarios to clearly understand the difference,similarity and how both can work in conjunction and all

Application Server is a term that sometimes is mixed with a web server. While a web server handles mainly HTTP protocols, the application server deals with several different protocols, including, but not limited, to HTTP.

The Web server's main job is to display the site content and the application server is in charge of the logic, the interaction between the user and the displayed content. The application server is working in conjunction with the web server, where one displays and the other one interacts.

The information traveling back and forth between the server and its client is not restricted to simple display markup, but to interaction between the two.

In most cases, the server creates this interaction through a component API, such as J2EE (Java 2 Platform), EJB (Enterprise JavaBean) and other different application software models.

An example:

The best way to understand the difference between the scenarios where an application server works with the web server versus a scenario where there isn't an application server is through an online store.

Scenario 1: Web server without an application server

you have an online store with only a web server and no application server. The site will provide a display where you can choose a product from. When you submit a query, the site performs a lookup and returns an HTML result back to its client. The web server sends your query directly to the database server (be patient, I will explain this one in our next nugget) and waits for a response. Once received, the web server formulates the response into an HTML file and sends it to your web browser. This back and forth communication between the server and database server happens every time a query is run.

Scenario 2: Web server with an application server

if the query you want to run has already been done previously and no data has changed since then, the server will generate the results without having to send the request to the database server. This allows a real-time query where a second client can access the same info and receive real time, reliable information without sending another duplicate query to the database server. The server basically acts as an intermediate between the database server and the web server. This allows the information pulled to be reusable while in the first scenario, since this info is embedded in a particular and "customized" HTML page, this is not a reusable process. A second client will have to request the info again and receive another HTML embedded page with the info requested -highly inefficient. Not to mention that this type of server is very flexible due to its ability to manage its own resources, including security, transaction processing, messaging and resource pooling.

To support such a variety of complex tasks this server must have a built in redundancy, great processing power and high amount of RAM to handle all the data it's pulling in real time.

Hope this helps.

• That's not accurate/confusing, even for web applications (i.e. the term application-server applies to none-web apps). Considering web only: A web server includes software (apache, nginx) to handle web requests (http). An application server contains/exposes the application (e.g. php code). They might be the same machine, they might not - for example it'd be considered normal to have nginx on one machine (web server) forwarding requests to php-fpm on a different machine (application server) which doesn't itself have any http access (only exposing the port for php-fpm itself). - AD7six
• @AD7six A Web server exclusively handles HTTP requests, whereas an application server handles business logic to application programs through any number of protocols including HTTP. - Durai Amuthan.H
• My point there is the application server may handle http requests, it's by no means a requirement. the application server deals with several different protocols, including, but not limited, to HTTP <- that says it definitely does handle http requests - that's not accurate. - AD7six
• After re-reading the examples given, I don't see any real clarity here - the descriptions relate mostly to caching. What aught to be clear is that a webserver is software, an application is software. if they are deployed on the same machine the machine can be referred to however you like. If they are on different machines it would be normal to refer to the one running the webserver as the webserver, and the one running the app as the appserver. You'd normally split things according to load and load balancing. Overall I find this answer doesn't add anything useful. - AD7six
• @AD7six My answer is meant to complement the other answers i.e others answers already mean what you have asked its just an extension to that. - Durai Amuthan.H

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.

• Very clear answer. But can you elaborate a little more about the 'new tricks' that allowed a web server to perform as an application server. - Quazi Irfan
• "new tricks" implies, running server side logic. Scripting logic like ASP or others. The original "web servers" just returned static content, from the filesystem. We've come a long way from that, now. - Cheeso

Web server

Run python -m 'SimpleHTTPServer' and go to http://localhost:8080. What you see is a web server at its workings. The server simply serves files over HTTP stored on your computer. The key point is that all this is done on top of the HTTP protocol. There also exist FTP servers for example which do exactly the same thing (serving stored files) but on top of a different protocol.

Application server

Say we have a tiny application like below (snippet from Flask).

@app.route('/')
def homepage():
    return '<html>My homepage</html>'

@app.route('/about')
def about():
    return '<html>My name is John</html>'

The small example program maps the URL / to the function homepage() and the /about to the function about().

To run this code we need an application server - a program or module that can listen for requests from a client and using our code, return something dynamically. In the example we simply return some very bad HTML.

What's the business logic all the other people talk about? Well, since a URL maps to somewhere specifically in our codebase, we are hypothetically showing some logic about how our program works.

Recapping

web server - serves files stored somewhere (most commonly .css, .html, .js). Common web servers are Apache, Nginx or even Python's SimpleHTTPServer.

application server - serves files generated on the fly. Essentially most web servers have some sort of plugins or even come with built-in functionality to do that. There exist also strict application servers like Gunicorn (Python), Unicorn (Ruby), uWSGI (Python), etc.

Notice that you can actually build a web server with the code of the application server. This is done in some cases during development where you do not want to have a gazillion of different servers running on your computer.

• This is the best and most succinct answer. I was wondering whether a web server could be considered a subset of an application server. Right now I'm thinking of it as a web server is like a getter method and an application server is like a factory method (where the URL is a constructor argument :D) - user7917402
• Uff.. Finally, thanks for giving a Python perspective. As language agnostic as this topic may seem, it is not. Someone who has never used EJB will not understand the Java oriented answers clearly. - Vikas

As many have said before, web servers handle HTTP petitions, while application servers handle petitions for distributed components. So, maybe the easiest way to understand the difference is to compare the two products in regards to programming environment they offer.

Web Server -> Programming Environment

IIS : ASP (.NET)

Tomcat : Servlet

Jetty : Servlet

Apache : Php, CGI

Application Servers -> Programming Environment

MTS : COM+

WAS : EJB

JBoss : EJB

WebLogic Application Server : EJB

The crucial difference is that application servers support some distributed component technology, providing features like remote invocation and distributed transactions, like EJB in Java world or COM+ on Microsoft platform. Http server often support some more simple programming environments, often scripting, like ASP (.NET) in case of Microsoft or Servlet--based, including JSP and many other in case of Java or PHP and CGI in case of Apache.

Other capabilities like load-balancing, clustering, session-failover, connection pooling etc. that used to be in the realm of application servers, are becoming available on web servers as well directly or through some third party products.

Finally, it is worth noting that the picture is further distorted with "lightweight containers" like Spring Framework, that often supplement the purpose of application servers in more simple manner and without the application server infrastructure. And since distribution aspect in applications is moving from distributed component towards service paradigm and SOA architecture, there is less and less space left for traditional application servers.

• Can any of the application servers you listed be used as a http web servers like apache http? - LearningMath

A Web server exclusively handles HTTP/HTTPS requests. It serves content to the web using HTTP/HTTPS protocol.

An application server serves business logic to application programs through any number of protocols, possibly including HTTP. The application program can use this logic just as it would call a method on an object. In most cases, the server exposes this business logic through a component API, such as the EJB (Enterprise JavaBean) component model found on Java EE (Java Platform, Enterprise Edition) application servers. The main point is that the web server exposes everything through the http protocol, while the application server is not restricted to it. An application server thus offers much more services than an web server which typically include:

• A (proprietary or not) API
• Load balancing, fail over...
• Object life cycle management
• State management (session)
• Resource management (e.g. connection pools to database)

Most of the application servers have Web Server as integral part of them, that means App Server can do whatever Web Server is capable of. Additionally App Server have components and features to support Application level services such as Connection Pooling, Object Pooling, Transaction Support, Messaging services etc.

An application server can (but doesn't always) run on a web server to execute program logic, the results of which can then be delivered by the web server. That's one example of a web server/application server scenario. A good example in the Microsoft world is the Internet Information Server / SharePoint Server relationship. IIS is a web server; SharePoint is an application server. SharePoint sits "on top" of IIS, executes specific logic, and serves the results via IIS. In the Java world, there's a similar scenario with Apache and Tomcat, for example.

As web servers are well suited for static content and app servers for dynamic content, most of the production environments have web server acting as reverse proxy to app server. That means while service a page request, static contents such as images/Static html is served by web server that interprets the request. Using some kind of filtering technique (mostly extension of requested resource) web server identifies dynamic content request and transparently forwards to app server.

Example of such configuration is Apache HTTP Server and BEA WebLogic Server. Apache HTTP Server is Web Server and BEA WebLogic is Application Server. In some cases, the servers are tightly integrated such as IIS and .NET Runtime. IIS is web server. when equipped with .NET runtime environment IIS is capable of providing application services

Web Server                               Programming Environment
Apache                                   PHP, CGI
IIS (Internet Information Server)        ASP (.NET)
Tomcat                                   Servlet
Jetty                                    Servlet

Application Server                       Programming Environment
WAS (IBM's WebSphere Application Server) EJB
WebLogic Application Server (Oracle's)   EJB
JBoss AS                                 EJB
MTS                                      COM+

In short a web server is a server that serves web pages to users via http. An application server is a server that hosts the business logic for a system. It often hosts both long running/batch processes and/or a interop services not meant for human consumption (REST/JSON services, SOAP, RPC, etc).

• What does the term 'host's the business logic' mean? How is it performed? - TwiggedToday
• Is the business logic exposed to the client through web services? - TwiggedToday
• It can be served via web-services, or it can be served by any other interface (TCP, MQ, flat files on a share (I don't recommend the last)). - C. Ross
• This can be misleading. The application server doesn't host anything. Your code hosts the business logic and the application server works as the glue between that and the web pages that users request. - Pithikos

The main difference between Web server and application server is that web server is meant to serve static pages e.g. HTML and CSS, while Application Server is responsible for generating dynamic content by executing server side code e.g. JSP, Servlet or EJB.

Which one should i use?
Once you know the difference between web and application server and web containers, it's easy to figure out when to use them. You need a web server like Apache HTTPD if you are serving static web pages. If you have a Java application with just JSP and Servlet to generate dynamic content then you need web containers like Tomcat or Jetty. While, if you have Java EE application using EJB, distributed transaction, messaging and other fancy features than you need a full fledged application server like JBoss, WebSphere or Oracle's WebLogic.

Web container is a part of Web Server and the Web Server is a part of Application Server.

Web Server is composed of web container, while Application Server is composed of web container as well as EJB container.

An application server is typically designed and deployed to facilitate longer running processes that will also be more resource intensive.

A web server is used for short bursts that are not resource intensive, generally. This is mostly to facilitate serving up web based traffic.

A web server runs the HTTP protocol to serve web pages. An application server can (but doesn't always) run on a web server to execute program logic, the results of which can then be delivered by the web server. That's one example of a web server/application server scenario.

A good example in the Microsoft world is the Internet Information Server / SharePoint Server relationship. IIS is a web server; SharePoint is an application server. SharePoint sits "on top" of IIS, executes specific logic, and serves the results via IIS.

In the Java world, there's a similar scenario with Apache and Tomcat, for example.

On a first hand, a web server serves web content (HTML and static content) over the HTTP protocol. On the other hand, an application server is a container upon which you can build and expose business logic and processes to client applications through various protocols including HTTP in a n-tier architecture.

An application server thus offers much more services than an web server which typically include:

• A (proprietary or not) API
• Object life cycle management,
• State management (session),
• Resource management (e.g. connection pools to database),
• Load balancing, fail over...

AFAIK, ATG Dynamo was one of the very first application server in late 90's (according to the definition above). In early 2000, it was the reign of some proprietary application servers like ColdFusion (CFML AS), BroadVision (Server-side JavaScript AS), etc. But none really survived the Java application server era.

The border between these two are getting ever so thinner.

Application servers exposes business logic to a client. So its like application server comprises of a set of methods(not necessarily though, can even be a networked computer allowing many to run software on it) to perform business logic. So it will simply output the desired results, not HTML content. (similar to a method call). So it is not strictly HTTP based.

But web servers passes HTML content to web browsers (Strictly HTTP based). Web servers were capable of handling only the static web resources, but the emergence of server side scripting helped web servers to handle dynamic contents as well. Where web server takes the request and directs it to the script (PHP, JSP, CGI scripts, etc.) to CREATE HTML content to be sent to the client. Then web server knows how to send them back to client. BECAUSE that's what a web server really knows.

Having said that, nowadays developers use both of these together. Where web server takes the request and then calls a script to create the HTML, BUT script will again call an application server LOGIC (e.g. Retrieve transaction details) to fill the HTML content.

So in this case both the servers were used effectively.

Therefore .... We can fairly safely say that in nowadays, in most of the cases, web servers are used as a subset of application servers. BUT theatrically it is NOT the case.

I have read many articles about this topic and found this article quite handy.

In Java terms there's one more: web container (or more strictly, servlet container). It's, say, in between web server and application server. A web container in Java terms is an application server which basically only implements the JSP/Servlet part of Java EE and lacks several core parts of Java EE, such as EJB support. An example is Apache Tomcat.

An application server is a machine (an executable process running on some machine, actually) that "listens" (on any channel, using any protocol), for requests from clients for whatever service it provides, and then does something based on those requests. (may or may not involve a respose to the client)

A Web server is process running on a machine that "listens" specifically on TCP/IP Channel using one of the "internet" protocols, (http, https, ftp, etc..) and does whatever it does based on those incoming requests... Generally, (as origianly defined), it fetched/generated and returned an html web page to the client, either fetched from a static html file on the server, or constructed dynamically based on parameters in the incoming client request.

• can u please give examples for bath cases. - frewper
• Can you please provide examples of both? Thanks. - LearningMath

All of the above is just over-complicating something very simple. An application server contains a web server, an application server just has a couple more additions/extensions to it than standard web servers. If you look at TomEE as an example:

CDI - Apache OpenWebBeans
EJB - Apache OpenEJB
JPA - Apache OpenJPA
JSF - Apache MyFaces
JSP - Apache Tomcat
JSTL - Apache Tomcat
JTA - Apache Geronimo Transaction
Servlet - Apache Tomcat
Javamail - Apache Geronimo JavaMail
Bean Validation - Apache BVal

You will see that Tomcat (Web container/server) is just another tool in the app servers arsenal. You can get JPA and the other tech in the web server as well if you want, but the application servers just package all of these things for your convenience. To be fully classified as an app server you essentially need to comply with a list of tools set forth by some standard.

Biggest difference is a Web Server handles HTTP requests, while an Application server will execute business logic on any number of protocols.

There is not necessarily a clear dividing line. Nowadays, many programs combine elements of both - serving http requests (web server) and handling business logic (app server)

Actually Apache is a web server and Tomcat is an application server. When as HTTP request comes to web server. Then static contents send back to browser by web server. Is there and logic do to done, then that request send to the application server. after processing the logic then response send to web server and send to the client.

Application server and web server both are used to host web application. Web Server is deal with web container on the other hand Application Server is deal with web container as well as EJB (Enterprise JavaBean) container or COM+ container for Microsoft dot Net.

Web Server is designed to serve HTTP static Content like HTML, images etc. and for the dynamic content have plugins to support scripting languages like Perl, PHP, ASP, JSP etc and it is limited to HTTP protocol. Below servers can generate dynamic HTTP content.

Web Server's Programming Environment:

IIS : ASP (.NET)

Apache Tomcat: Servlet

Jetty: Servlet

Apache: Php, CGI

Application Server can do whatever Web Server is capable and listens using any protocol as well as App Server have components and features to support Application level services such as Connection Pooling, Object Pooling, Transaction Support, Messaging services etc.

Application Server's Programming Environment:

MTS: COM+

WAS: EJB

JBoss: EJB

WebLogic Application Server: EJB

While there may be overlaps between the two (some web servers may even be used as application servers) the biggest difference IMHO is in the processing model and the session management:

In Web server processing model, the focus is on handling requests; the notion of "session" is pretty much virtual. That is to say that "session" is simulated by transferring the representation of state between client and server (hence REST) and/or serializing it to an external persistent storage (SQL Server, Memcached etc).

In Application server the session is usually more explicit and often takes form of an object living in memory of the application server for the entire duration of the "session".

From https://en.wikipedia.org/wiki/Web_server

A web server is a computer system that processes requests via HTTP, the basic network protocol used to distribute information on the World Wide Web. The term can refer to the entire system, or specifically to the software that accepts and supervises the HTTP requests.

From https://en.wikipedia.org/wiki/Application_server#Application_Server_definition

An application server runs behind a web Server (e.g. Apache or Microsoft Internet Information Services (IIS)) and (almost always) in front of an SQL database (e.g. PostgreSQL, MySQL, or Oracle).

Web applications are computer code which run atop application servers and are written in the language(s) the application server supports and call the runtime libraries and components the application server offers.

It depends on the specific architecture. Some application servers may use web protocols natively (XML/RPC/SOAP over HTTP), so there is little technical difference. Typically a web server is user-facing, serving a variety of content over HTTP/HTTPS, while an application server is not user-facing and may use non-standard or non-routable protocols. Of course with RIA/AJAX, the difference could be further clouded, serving only non-HTML content (JSON/XML) to clients pumping particular remote access services.

IMO, it's mostly about separating concerns.

From a purely technical point of view, you can do everything (web content + business logic) in a single web server. If you'd do that, then the information would be embedded inside requested the HTML content. What would be the impact?

For example, imagine you have 2 different apps which renders entirely different HTML content on the browser. If you would separate the business logic into an app-server than you could provide different web-servers looking up the same data in the app-server via scripts. However, If you wouldn't separate the logic and keep it in the web-server, whenever you change your business model, you would end up changing it in every single web-server you have which would take more time, be less reliable and error-prone.