Understanding Nginx Server Blocks: How DNS and IP Address Access Affect Your Web Application

Understanding Nginx Server Blocks: How DNS and IP Address Access Affect Your Web Application

When you set up a web server, whether for personal projects or for professional web applications, understanding how your server handles different types of requests is crucial. This knowledge becomes especially pertinent when dealing with Nginx, a popular web server used for its high performance and flexibility in hosting multiple websites on a single machine. A common scenario that puzzles many is why accessing a server directly via its public IP address only yields a default Nginx message, while accessing the same server through a DNS A record displays the intended application. Let’s dive into the mechanics behind this behavior and how Nginx’s server blocks play a pivotal role.

The Role of Nginx Server Blocks

Server blocks, known in Apache as virtual hosts, are the cornerstone of Nginx’s ability to host multiple domains from a single server. Each block can be configured with specific rules to handle requests for different domain names. This functionality enables Nginx to serve the correct content based on the incoming request’s domain name.

Encounter with the Default Server Block

Upon installing Nginx, you will find that it includes a default server block. This default is essentially a fallback for requests that do not match any other custom-configured server blocks. Typically, when you access the server via its public IP address, Nginx doesn’t find a matching server block for the IP and thus serves the content defined in the default block, which is usually a basic Nginx greeting page.

Custom Server Blocks and DNS A Records

For your application to be accessible via a domain name, a DNS A record is created to point the domain to your server’s IP address. Alongside, a corresponding server block is set up in Nginx to serve your application when requests to your domain name are received. This server block specifies the server name (your domain) and the location of the application files, guiding Nginx to serve the correct content.

Understanding the Behavior Discrepancy

  • Access via Public IP: Direct IP access doesn’t carry the domain name in the request, leading Nginx to resort to the default server block, thus presenting the default Nginx page.
  • Access via DNS A Record: Here, the request includes the domain name, allowing Nginx to match this request with the configured server block for your domain, consequently serving your application.

Addressing the IP Access Scenario

If you wish for the public IP address access to display your application, there are a couple of approaches:

  • Modify the Application’s Server Block: Add the public IP address to the server_name directive in your application’s server block configuration.
  • Adjust the Default Server Block: Change the default server block to point towards your application’s directory.

However, for security, scalability, and maintenance reasons, it’s advisable to access and manage web applications through domain names. This practice not only simplifies SSL/TLS certificate management but also provides flexibility in server management and application deployment.


The distinction in behavior when accessing your server through a public IP address versus a domain name underscores the importance of Nginx server block configurations. By understanding and leveraging these configurations, you can control how your server responds to different requests, ensuring your applications are accessible in the manner you intend. Whether you’re a budding web developer or a seasoned system administrator, mastering Nginx server blocks will equip you with the tools to efficiently manage your web applications.