How Does Web Server Communicate With Application Server?


Larry Thompson

How Does Web Server Communicate With Application Server?

When building a web application, it is common to have separate servers for handling different tasks. The web server is responsible for serving static content such as HTML, CSS, and JavaScript files, while the application server handles dynamic content and executes server-side code. In this article, we will explore how these two servers communicate with each other to deliver a seamless user experience.

The Role of the Web Server

The web server’s main job is to receive and respond to HTTP requests from clients (typically web browsers). It listens on a specific port (usually port 80 for HTTP or port 443 for HTTPS) for incoming requests. When a request arrives, the web server examines the requested URL and determines how to handle it.

Static Content Delivery:

  • The most common scenario is when the requested URL corresponds to a static file such as an HTML document or an image. In this case, the web server simply retrieves the file from its file system and sends it back as a response to the client.
  • Web servers like Apache or Nginx are commonly used for delivering static content efficiently.

Reverse Proxy:

  • In some cases, especially in complex applications with multiple servers, the web server acts as a reverse proxy.
  • A reverse proxy receives requests from clients and forwards them to the appropriate backend server based on certain rules or configurations.
  • This setup allows the web server to handle tasks like load balancing or caching while offloading dynamic processing to application servers.

The Role of the Application Server

Dynamic Content Processing:

The application server hosts the business logic and processes dynamic content. It receives requests from the web server and generates responses based on the application’s code and data.

Server-Side Technologies:

  • Application servers are responsible for executing server-side code written in languages such as Java, Python, PHP, or Node.js.
  • They provide an environment where applications can run, process data, interact with databases, and perform other necessary operations.

Communicating with Web Server:

There are different ways for web servers to communicate with application servers:

  • HTTP-Based Communication:
    • The simplest approach is using HTTP-based communication protocols like CGI (Common Gateway Interface) or FastCGI.
    • In this setup, the web server forwards the request to the application server using a predefined protocol.
    • The application server processes the request, generates a response, and sends it back to the web server over a socket connection.
  • Application Server as a Service:
    • In modern architectures, application servers are often designed as standalone services that expose APIs for communication.
    • The web server can make HTTP requests to these APIs to fetch data or trigger specific actions on the application server.
    • This decoupled approach allows developers to scale different parts of their applications independently and enables better modularization.


In summary, web servers and application servers work together in a client-server architecture to deliver dynamic content efficiently. The web server handles static content delivery and acts as a reverse proxy, forwarding requests to the appropriate application server.

The application server executes server-side code, processes dynamic content, and communicates with the web server using protocols like CGI or through APIs. Understanding this communication flow is essential for building scalable and robust web applications.

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