Why virtual hosting serves multiple domains in Nginx - Visual Breakdown

Process Flow - Why virtual hosting serves multiple domains

Client sends HTTP request

↓

Server receives request

↓

Check Host header in request

↓

Match Host to server block

↓

Serve domain A content

↓

Serve domain B content

↓

Serve default content if no match

↓

Send response to client

The server uses the Host header in the request to decide which domain's content to serve, enabling multiple domains on one server.

Execution Sample

Nginx

server {
  listen 80;
  server_name example.com;
  root /var/www/example;
}

server {
  listen 80;
  server_name test.com;
  root /var/www/test;
}

Two server blocks listen on port 80 and serve different content based on the requested domain name.

Process Table

Step	Client Request Host	Server Block Matched	Content Served	Action
1	example.com	server_name example.com	/var/www/example content	Serve example.com site
2	test.com	server_name test.com	/var/www/test content	Serve test.com site
3	unknown.com	No match	Default server content	Serve default site
4	example.com	server_name example.com	/var/www/example content	Serve example.com site

💡 Requests are matched by Host header; if no match, default server block serves content.

Status Tracker

Variable	Start	After 1	After 2	After 3	After 4
Host header	none	example.com	test.com	unknown.com	example.com
Matched server block	none	example.com block	test.com block	default block	example.com block
Content served	none	/var/www/example	/var/www/test	default content	/var/www/example

Key Moments - 2 Insights

Why does the server use the Host header to decide which content to serve?

Because multiple domains share the same IP and port, the Host header tells the server which domain the client wants, as shown in execution_table rows 1 and 2.

What happens if the Host header does not match any server_name?

The server uses the default server block to serve content, as seen in execution_table row 3.

Visual Quiz - 3 Questions

Look at the execution table, what content is served when the Host header is 'test.com'?

A /var/www/example content

B /var/www/test content

C Default server content

D No content served

💡 Hint

Check execution_table row 2 under 'Content Served'

At which step does the server serve the default content?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at execution_table row 3 under 'Content Served'

If a new domain 'newsite.com' is added with its own server block, what changes in the variable tracker after a request to 'newsite.com'?

A Host header changes to 'newsite.com' and matched server block changes accordingly

B Host header remains the same but content served changes

C No change because server only serves example.com and test.com

D Content served becomes default for all requests

💡 Hint

Refer to variable_tracker rows for 'Host header' and 'Matched server block'

Concept Snapshot

Virtual hosting lets one server handle many domains.
It uses the Host header in HTTP requests to pick the right site.
Each domain has a server block with server_name and root.
If no match, default server block serves content.
This saves IP addresses and simplifies hosting multiple sites.

Full Transcript

Virtual hosting allows a single web server to serve multiple domain names by checking the Host header in each incoming HTTP request. The server compares this header to the server_name directives in its configuration. When a match is found, the server serves the content from the corresponding root directory. If no match is found, the default server block handles the request. This method enables efficient use of one IP address to host many websites.