Default server handling in Nginx - Commands & Configuration

Introduction

When multiple websites or services run on the same server, the web server needs to know which site to show if a visitor does not specify a site name. Default server handling tells the web server which site to show by default when no specific site matches the visitor's request.

When you host multiple websites on one server and want to control which site visitors see if they use the server's IP address or an unknown domain.

When you want to avoid showing an error page if a visitor types a wrong or missing domain name.

When you want to provide a simple landing page or message for all unmatched requests.

When you want to improve security by not revealing other hosted sites when the domain is unknown.

When you want to log or track requests that do not match any configured site.

Config File - nginx.conf

nginx.conf

server {
    listen 80 default_server;
    listen [::]:80 default_server;

    server_name _;

    root /var/www/default;
    index index.html;

    location / {
        try_files $uri $uri/ =404;
    }
}

This configuration defines a default server block for Nginx.

• listen 80 default_server; tells Nginx this server block is the default for IPv4 port 80.
• listen [::]:80 default_server; does the same for IPv6.
• server_name _; matches any hostname not matched by other server blocks.
• root /var/www/default; sets the folder where the default website files are stored.
• location / handles all requests by trying to serve files or returning a 404 if not found.

Commands

Create the directory to hold the default website files.

Terminal

sudo mkdir -p /var/www/default

Expected Output

No output (command runs silently)

Create a simple index.html file to show a welcome message on the default site.

Terminal

echo '<html><body><h1>Welcome to the default site</h1></body></html>' | sudo tee /var/www/default/index.html

Expected Output

<html><body><h1>Welcome to the default site</h1></body></html>

Test the Nginx configuration for syntax errors before reloading.

Terminal

sudo nginx -t

Expected Output

nginx: the configuration file /etc/nginx/nginx.conf syntax is ok

nginx: configuration file /etc/nginx/nginx.conf test is successful

Reload Nginx to apply the new default server configuration without downtime.

Terminal

sudo systemctl reload nginx

Expected Output

No output (command runs silently)

Check that the default site is served when accessing the server without a specific hostname.

Terminal

curl -s http://localhost

Expected Output

<html><body><h1>Welcome to the default site</h1></body></html>

Key Concept

If you remember nothing else from this pattern, remember: the default server block catches all unmatched requests and shows a fallback site or message.

Common Mistakes

Not setting the 'default_server' flag on any listen directive.

Nginx will not know which server block to use as default, so unmatched requests may cause errors or unexpected sites to show.

Add 'default_server' to the listen directive in the server block you want as default.

Using an incorrect or missing root directory for the default server.

Nginx cannot find the files to serve, resulting in 404 errors.

Ensure the root path exists and contains an index.html or other valid files.

Not testing the Nginx configuration before reloading.

Syntax errors can cause Nginx to fail to reload, leading to downtime.

Always run 'nginx -t' to verify configuration before reloading.

Summary

Create a server block with 'default_server' in the listen directive to catch unmatched requests.

Set a valid root directory with an index.html file to serve a default page.

Test the Nginx configuration with 'nginx -t' before reloading to avoid errors.

Reload Nginx to apply changes without downtime.

Verify the default site by accessing the server without a specific hostname.

Practice

1. What does the default_server directive do in an nginx configuration?

easy

A. It sets the server block to only respond to HTTPS requests.

B. It disables the server block from responding to any requests.

C. It redirects all requests to another server block.

D. It marks the server block to respond when no other server name matches the request.

Solution

1. Step 1: Understand the role of default_server

   The default_server directive in the listen line tells nginx which server block to use if no other server name matches the request.

2. Step 2: Analyze the options

   It marks the server block to respond when no other server name matches the request. correctly describes this behavior. Options A, B, and D describe unrelated or incorrect behaviors.

3. Final Answer:

   It marks the server block to respond when no other server name matches the request. -> Option D

4. Quick Check:

   default_server = marks fallback server [OK]

Hint: default_server means fallback server for unmatched requests [OK]

Common Mistakes:

• Thinking default_server disables the server
• Confusing default_server with HTTPS enforcement
• Assuming default_server redirects requests

2. Which of the following is the correct syntax to set a server block as the default server for HTTP on port 80?

easy

A. listen default_server 80;

B. listen 80 default_server;

C. default_server listen 80;

D. listen 80 default;

Solution

1. Step 1: Recall nginx listen directive syntax

   The correct syntax places the port number first, then the default_server flag: listen 80 default_server;.

2. Step 2: Evaluate each option

   listen 80 default_server; matches the correct syntax. Options A and C have incorrect order. listen 80 default; uses an invalid keyword default.

3. Final Answer:

   listen 80 default_server; -> Option B

4. Quick Check:

   listen port default_server order matters [OK]

Hint: Put port number before default_server in listen line [OK]

Common Mistakes:

• Swapping order of port and default_server
• Using invalid keywords like default instead of default_server
• Placing default_server outside listen directive

3. Given this nginx config snippet, what response will nginx serve for a request to IP address 192.168.1.10?

server {
    listen 80 default_server;
    server_name default.example.com;
    return 200 'Default Server';
}

server {
    listen 80;
    server_name site.example.com;
    return 200 'Site Server';
}

medium

A. Returns 'Default Server'

B. Returns 'Site Server'

C. Returns 404 Not Found

D. Returns 500 Internal Server Error

Solution

1. Step 1: Identify which server block matches the IP request

   The request is to IP 192.168.1.10, which does not match any server_name directive.

2. Step 2: Determine which server handles unmatched requests

   The server block with listen 80 default_server; handles requests without matching server_name, so it responds.

3. Final Answer:

   Returns 'Default Server' -> Option A

4. Quick Check:

   IP requests hit default_server block [OK]

Hint: Requests without matching server_name go to default_server [OK]

Common Mistakes:

• Assuming IP requests match any server_name
• Thinking unmatched requests return 404 automatically
• Confusing default_server with error handling

4. You configured two server blocks both with listen 80 default_server;. What will happen when nginx starts?

medium

A. nginx will fail to start due to conflicting default_server directives.

B. nginx will pick the first default_server block and ignore the second.

C. nginx will load both and round-robin requests between them.

D. nginx will merge both server blocks into one.

Solution

1. Step 1: Understand default_server uniqueness

   Only one server block per IP:port can be marked as default_server. Multiple default_server flags on same port cause conflict.

2. Step 2: Check nginx behavior on conflict

   nginx detects this conflict and refuses to start, showing an error about duplicate default_server.

3. Final Answer:

   nginx will fail to start due to conflicting default_server directives. -> Option A

4. Quick Check:

   Only one default_server per port allowed [OK]

Hint: Only one default_server per port; duplicates cause startup error [OK]

Common Mistakes:

• Thinking nginx picks one silently
• Assuming nginx load balances default_server blocks
• Believing nginx merges server blocks automatically

5. You want nginx to serve a custom page for all requests that do not match any server_name, including requests by IP or unknown hostnames. How should you configure the default server block to achieve this?

hard

A. Use listen 80 default_server; and set server_name localhost;.

B. Use listen 80; without default_server and set server_name _;.

C. Use listen 80 default_server; and set server_name _; with a custom return or root directive.

D. Use listen 80 default_server; and omit server_name entirely.

Solution

1. Step 1: Mark the server block as default_server

   To catch unmatched requests, the server block must have listen 80 default_server;.

2. Step 2: Use server_name _; as a wildcard

   Setting server_name _; is a common convention to match any hostname not matched elsewhere.

3. Step 3: Configure custom response

   Inside this block, use return or root to serve the custom page.

4. Final Answer:

   Use listen 80 default_server; and set server_name _; with a custom return or root directive. -> Option C

5. Quick Check:

   default_server + server_name _ = catch-all server [OK]

Hint: default_server plus server_name _ catches all unmatched requests [OK]

Common Mistakes:

• Not using default_server flag
• Omitting server_name or using localhost only
• Assuming default_server alone matches all hostnames