How Does Web Server Talk to App Server?


Scott Campbell

Web servers and application servers are essential components in the architecture of a web application. Understanding how these two servers communicate with each other is crucial for developers and system administrators. In this article, we will explore the mechanisms behind this communication and delve into the various methods employed.

What is a Web Server?
A web server is a software or hardware component that responds to HTTP requests from clients, typically web browsers. It is responsible for serving static content, such as HTML files, images, CSS stylesheets, and JavaScript files to clients. Popular web server software includes Apache HTTP Server, NGINX, and Microsoft Internet Information Services (IIS).

What is an Application Server?
An application server is a server that hosts applications and provides services required by those applications to function properly. These services may include database access, security management, transaction processing, and more.

Application servers are responsible for executing dynamic code and generating dynamic content. Examples of application servers include Apache Tomcat, JBoss/WildFly, and IBM WebSphere.

Methods of Communication

1. HTTP Requests

The most common method of communication between web servers and application servers is through HTTP requests. When a client initiates an HTTP request to the web server, the request may contain dynamic content parameters or specific instructions that require processing on the application server.

Once the web server receives such a request requiring application-level processing, it forwards the request to the appropriate application server using various protocols such as:

  • CGI (Common Gateway Interface): One of the oldest methods used for communication between web servers and application servers.
  • FastCGI: An improved version of CGI that reduces overhead by maintaining persistent connections between web servers and application servers.
  • AJP (Apache JServ Protocol): A binary protocol used specifically for communication between Apache web servers and Tomcat application servers.
  • HTTP Proxy: Web servers can act as proxies, forwarding requests to application servers based on URL patterns or other rules.

2. Reverse Proxy

A reverse proxy is a server that sits between the client and the application server. It receives requests from clients and forwards them to the appropriate application server based on various criteria, such as load balancing, caching, or security.

The reverse proxy can handle tasks such as SSL termination, compression, and routing. It acts as an intermediary, shielding the application server from direct client connections. Popular reverse proxy software includes NGINX and Apache HTTP Server with mod_proxy.

3. WebSockets

WebSockets provide a bidirectional communication channel between clients (typically web browsers) and servers. Unlike traditional HTTP requests that follow a request-response model, WebSockets allow for real-time data transfer between the client and server.

While web servers may not directly communicate with application servers using WebSockets, they can act as intermediaries by forwarding WebSocket connections to the appropriate backend server.


In conclusion, web servers and application servers communicate through various methods such as HTTP requests, reverse proxies, and WebSockets. These mechanisms enable dynamic content generation and processing on application servers while ensuring efficient delivery of static content by web servers.

Understanding how these components interact is crucial for developers designing scalable web applications and system administrators managing their infrastructure. By utilizing these methods effectively, developers can create robust systems that deliver dynamic content seamlessly to clients while maintaining high performance and scalability.

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