Web servers and application servers are technologies that enable the exchange of data and services over the Internet. The client-server architecture is the basic mechanism of the Internet. When you visit a website or app, your browser (as a client) requests data from a remote server and displays the response. A web server is a software component that serves static data, such as images, files, and text, in response to client requests. The application server adds business logic to compute the web server's response. Both terms are used interchangeably, and the most popular server software solutions today are hybrid web application servers.
How they work: web server or application server
Web servers and application servers have different independent processes. However, they are invisible to the end user.
How a web server works
A web server is the technology that hosts a website's code and data. When you enter a URL in a browser, that URL is actually the address identifier of the web server.
Your browser and web server interact as follows.
The browser uses the URL to find the IP address of the server
The browser sends an HTTP request for information
The web server communicates with the database server to find the relevant data
A web server returns static content, such as HTML pages, images, videos, or files, to the browser in an HTTP response
The browser then displays the information to you
A website that hosts static content such as blogs, header images, or articles can run on a web server. However, most websites and web applications are much more interactive and require an application server.
How an application server works
The application server extends the capabilities of the web server by supporting dynamic content generation, application logic, and integration with various resources. It provides a runtime environment in which application code can run and interact with other software components, such as messaging systems and databases. It uses business logic to transform data more efficiently than a web server.
When you try to access interactive content on a website, the process is as follows.
The browser uses the URL to find the IP address of the server
The browser sends an HTTP request for information
The web server forwards the request to the application server
The application server applies business logic and interacts with other servers and third-party systems to fulfill the request
The application server renders a new HTML page and returns it as a response to the web server
The web server returns a response to the browser
The browser displays the information for you
In the example of an e-commerce website, when you add items to your cart or checkout, you interact with the application server.
Key Differences: Web Server and Application Server
There are several key differences between web servers and application servers.
Tasks covered
A web server hosts websites and provides answers to simple queries. Web servers also log server activity and allow server-side scripting.
Application servers, on the other hand, have a more complex set of tasks. Application servers use business logic to create dynamic content by connecting to corporate systems, services, and databases.
Used protocols
The main protocol used by web servers is the HTTP protocol. However, various web servers also support FTP and Simple Mail Transfer Protocol (SMTP). These two protocols facilitate the storage and transfer of files, as well as e-mail.
In addition to the protocols used by web servers, application servers use additional protocols to communicate with other software components. For example, they can use Remote Method Invocation (RMI) and Remote Procedure Call (RPC).
Types of content
Web servers mostly provide static content. Static content is content that does not need to be modified or processed by the server before being sent. For example, image files (such as PNG, GIF, and JPEG), downloadable documents (PDF files), videos, and HTML files are static content.
Application servers mainly serve dynamic content. Dynamic content is content that changes depending on how the user interacts with it. For example, dynamically generated reports, customizable data views, personalized user interfaces, database results, and processed HTML code are all dynamic content.
Multithreading
Threads on the server are separate work paths that ensure parallel processing of tasks. In multi-threaded mode, the server creates and runs multiple threads at the same time, each of which processes a separate task or part of a task. Multi-threading support helps deliver web content faster while handling large web traffic.
Most web servers do not support multithreading. Web servers place each new connection request on a queue and use an event loop to track new entries and dequeues. To improve efficiency, the server processes requests using non-blocking I/O operations and callbacks. Non-blocking operations and an event-driven architecture enable web servers to handle parallel connections.
Application servers use multithreading to provide high scalability and efficiency. If a request requires external resources, the application server uses separate threads to cover these interactions. It can handle multiple threads simultaneously, serving multiple client interactions in parallel.
How do application servers and web servers interact?
Application servers and web servers work together to process client requests and deliver content to the user. The web server always receives a new request first. If it can generate the information itself, it does so and sends an HTTP response. It also checks to see if there is any data that the user has requested in the cache.
If the web server cannot access the content the user wants, it redirects the request to the application server. The application server processes the data and uses business logic to provide the correct information. The request is then passed back to the web server, which forwards it to the user. In some architectures, application servers can also be configured to handle HTTP requests on their own.
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