Web Server vs. Application Server: What's the Difference?
In IT Operations, we often hear about web servers vs. application servers, and sometimes it seems like these terms are used interchangeably. Plus, many enterprise teams use both a web server and an app server, running the web server in front of the application server as a proxy. Understanding the use cases and differences between these two infrastructure technologies can be tricky.
In this blog, our expert explains the key differences between web servers vs. application servers, and gives some popular examples of each.
- What Is a Web Server?
- What Is an Application Server?
- Web Server vs. Application Server: Key Differences
- Popular Web and App Servers
- Final Thoughts
What Is a Web Server?
A web server receives HTTP requests and sends back an HTTP response. Depending on what was requested, the response could be anything from HTML, a video, an image, or a message redirecting the HTTP client to another URI.
The primary role of a web server is to parse HTTP requests and provide a response to a client. The web server may even utilize a server-side application to generate a dynamic response.
Web servers are tailored to be performant, responding to as many requests as possible in the shortest amount of time, with as little resource utilization as possible. To do this, they are designed with simplicity in mind. By default, when the web server receives a request, it will try to serve the requested file from the file system. For example, if my web server is configured to serve files from
/var/www/public/html, I can request a file index.html by sending an HTTP request to
mysite.com/index.html. If the file exists in
/var/www/public/html, the web server will read and transmit that file to the requesting client, along with some metadata known as HTTP response headers.
In a more advanced scenario, the web server may be configured to pass the request to a program capable of handling it appropriately. For example, I may have a perl application that renders a response to a request for
mysite.com/cgi-bin/todaysDatethat responds with a template showing the current date and time.
Ultimately, individual web servers are bound to IP addresses and ports, listening for requests on common ports like TCP/80 for HTTP and TCP/443 for HTTPS. They can have many unique names assigned to them, even on the same IP address and port, which is handled through a concept called virtual servers. Web servers also provide an environment where a server-side program, like PHP, perl, python, and others, can execute and send back responses.
Web servers are usually easy to configure. Many enterprise applications rely on web servers to directly respond to requests for static files, as opposed to dynamic files which are “proxied” to application servers. A static file is the same every time it’s requested —for example, the logo for a company’s website — and is generally a logical file on a directory on a disk attached to the web server. A dynamic response is generated every time the path is requested, like the perl example generating the date and time. The simplicity of a static request aids in the overall performance of a web server. A web server is designed to respond to a request rapidly, with little overhead.
When developers deploy web servers with application servers, they often keep the functionality of the web server and the application server separate. This is typically viewed as the best way to increase performance, as the web server fulfills the roll of rapidly responding to HTTP/S requests and the app server can be left to do what app server does best: generate dynamic content.
What Is an Application Server?
An application server is designed to respond to not only web-based requests (HTTP/S), but other protocols as well, delivering dynamic content over message buses, remoting, and other protocols. Application servers use these protocols to deploy and serve business applications. The purpose of application servers is to reduce the size and complexity of a deployment, as well as adding functionality out of the box, such as streamlined security.
While a web server mainly deals with sending static files to a web browser, the application server generates responses according to business logic that is dynamic, and can change depending on the parameters of the request from a web browser client.
As application server workloads are more complicated than web server workloads, they are usually configured to have more CPU, memory, and disk resources compared to web servers. Application servers often require load balancing, which helps to distribute requests to across multiple servers, distributing the entire applications current load and maximizing availability. Web servers are often placed in front of application servers to provide this load balancing functionality.
Application server functionality often includes features not found in web servers such as messaging, security, connection pooling to databases, support for transactions, batch processing, scheduled tasks, and job queues. Application servers can employ scalability strategies, like load balancing, and fault-tolerance techniques, like shared sessions, to enable high availability. These functionalities are often enabled by web servers, but require the application server to be configured to take advantage of the features (such as load balancing) that the web server, configured as a web proxy, provides. This allows application servers to handle increasing numbers of users simultaneously and sustain performance when traffic grows.
Web Server vs. Application Server: Key Differences
While an application server often times contains the functionality of a web server, most developers don’t deploy application servers for use as web servers to aid performance.
See the table below for a side-by-side web server vs. app server feature comparison.
Intended to be used for static content
Used for dynamic content
Utilizes fewer resources than an application server
Requires more resources than a web server
HTTP and HTTPS protocols
HTTP/S, in addition to RPC/RMI/Remoting, messaging, and other proprietary wireline protocols
Responds to HTTP requests with requested content
Dynamically generates a response for the requested resource
Serve over 10k concurrent requests, maximizing performance
Load needs to be balanced across many servers to serve many concurrent requests
Cannot access databases
Storage requirements are minimal
Typically larger storage requirements
Part of a wider business application strategy
Executes business logic, but needs web servers to scale
Popular Web and Application Servers
Apache HTTP Server
Often referred to as just "Apache," Apache HTTP Server has classically been considered the web server ideal for shared hosting environments, because of its ability for users to add configuration files for individual virtual servers and paths.
NGINX is a web server that can also serve as a load balancer, reverse proxy, and http cache. The non-blocking, event-driven architecture of NGINX makes it both fast and scalable, and it is frequently deployed in Kubernetes stacks.
Apache Tomcat is a lightweight, open source Java application server that serves as a reference implementation for servlet and Java Server Pages (JSPs).
Zend Serveris an application server for PHP-based applications. Zend Server supports Apache, NGINX, and IIS as its corresponding web server options. It also uses a dedicated lighttpd web server for its administration interface.
Other Web and App Servers
There are several other examples of app servers out there including JBoss, Glassfish, Weblogic, and Websphere, just to name a few. IIS is an application server for ASP.NET and C# applications, and lighttpd is another popular web server.
Hopefully it's clear by now that web servers and application servers have some functionality overlap, and one is not necessarily superior to the other. Depending on your needs and use case, it often makes sense to pair an application server like Tomcat or Zend Server with a web server like Apache or NGINX to enable high availability and scalable performance.
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