Default server handling in Nginx - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What happens when a request matches no server_name?

Given this nginx configuration snippet:

server {
    listen 80 default_server;
    server_name _;
    return 200 'Default server response';
}

server {
    listen 80;
    server_name example.com;
    return 200 'Example.com response';
}

What will be the response body when a request is sent to IP address directly (no Host header or unknown Host)?

Nginx

server {
    listen 80 default_server;
    server_name _;
    return 200 'Default server response';
}

server {
    listen 80;
    server_name example.com;
    return 200 'Example.com response';
}

A The response body will be 'Default server response'

B The response body will be 'Example.com response'

C The request will be rejected with 404 Not Found

D The request will timeout with no response

💡 Hint

Think about which server block nginx uses when no server_name matches.

Nginx uses the server block marked with 'default_server' for requests that don't match any server_name. Here, the first server block is the default, so it responds with 'Default server response'.

❓ Configuration

intermediate

Identify the correct default server configuration

Which nginx server block configuration correctly sets a default server for HTTP port 80?

A

server {
    listen 80 default_server;
    server_name _;
    return 200 'Default';
}

B

server {
    listen 80;
    server_name default_server;
    return 200 'Default';
}

C

server {
    listen 80 default;
    server_name _;
    return 200 'Default';
}

D

server {
    listen 80 default_server on;
    server_name _;
    return 200 'Default';
}

💡 Hint

The 'default_server' keyword must be used with 'listen'.

Only option A uses the correct syntax 'listen 80 default_server;' to mark the server block as default. Other options have invalid syntax or misuse the directive.

❓ Troubleshoot

advanced

Why does nginx serve the wrong server block?

You have two server blocks:

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

server {
    listen 80;
    server_name test.com;
    return 200 'Test.com';
}

You send a request with Host header 'test.com' but nginx responds with 'Example.com default'. What is the likely cause?

A The first server block is default_server and matches all requests, ignoring server_name

B The second server block has a syntax error and is ignored

C Nginx does not support multiple server blocks on the same port

D The Host header is missing in the request, so default_server is used

💡 Hint

Check if the Host header is correctly sent in the request.

If the Host header is missing or incorrect, nginx cannot match server_name and falls back to the default_server block. This causes the default server block to respond even if another server_name matches.

🔀 Workflow

advanced

Order the steps to set a default server in nginx

Put these steps in the correct order to configure a default server for HTTP requests in nginx:

A 1,3,2,4

B 2,1,3,4

C 1,2,3,4

D 1,2,4,3

💡 Hint

Think about editing config, then reloading, then testing.

First edit the config, then add the default_server directive, reload nginx to apply, and finally test the setup.

✅ Best Practice

expert

Which is the best practice for default server handling in nginx?

Choose the best practice for configuring a default server in nginx to handle unmatched requests safely and clearly.

A Use multiple server blocks with the same server_name and rely on nginx to load balance between them

B Use a dedicated server block with 'listen 80 default_server;' and a generic server_name like '_' that returns a simple 444 or 404 response

C Set the first server block without default_server and rely on nginx to pick the first block as default

D Do not configure a default server; let nginx return 502 Bad Gateway for unmatched requests

💡 Hint

Think about clarity and security for unmatched requests.

Best practice is to explicitly define a default server block with 'default_server' and a generic server_name like '_'. It should return a minimal response like 444 (connection closed) or 404 to avoid leaking information or serving unintended content.

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