Proxy headers in Nginx - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the original client's IP address in the proxy headers.

Nginx

proxy_set_header X-Real-IP [1];

Drag options to blanks, or click blank then click option'

A$http_user_agent

B$host

C$remote_addr

D$server_addr

Attempts:

3 left

💡 Hint

Common Mistakes

Using $host instead of $remote_addr causes the backend to see the server's hostname, not the client IP.

Using $server_addr sends the server's IP, not the client's.

The X-Real-IP header should be set to $remote_addr to pass the client's IP address to the backend server.

2fill in blank

medium

Complete the code to forward the original Host header to the backend server.

Nginx

proxy_set_header Host [1];

Drag options to blanks, or click blank then click option'

A$host

B$remote_addr

C$server_name

D$http_referer

Attempts:

3 left

💡 Hint

Common Mistakes

Using $remote_addr sends the client IP instead of the host.

Using $server_name sends the server's configured name, not the client's requested host.

The Host header should be set to $host to preserve the original host requested by the client.

3fill in blank

hard

Fix the error in the code to correctly set the X-Forwarded-For header to include the client IP and existing forwarded IPs.

Nginx

proxy_set_header X-Forwarded-For [1];

Drag options to blanks, or click blank then click option'

A$http_x_forwarded_for

B$server_addr

C$remote_addr

D$proxy_add_x_forwarded_for

Attempts:

3 left

💡 Hint

Common Mistakes

Using $remote_addr overwrites the existing forwarded IPs.

Using $http_x_forwarded_for alone does not add the current client IP.

The variable $proxy_add_x_forwarded_for appends the client IP to the existing X-Forwarded-For header, preserving the chain of IPs.

4fill in blank

hard

Fill both blanks to set headers that forward the original protocol and client IP to the backend.

Nginx

proxy_set_header X-Forwarded-Proto [1];
proxy_set_header X-Real-IP [2];

Drag options to blanks, or click blank then click option'

A$scheme

B$remote_addr

C$host

D$server_name

Attempts:

3 left

💡 Hint

Common Mistakes

Using $host for X-Forwarded-Proto is incorrect.

Using $server_name for X-Real-IP sends the server name, not client IP.

X-Forwarded-Proto should be set to $scheme to indicate HTTP or HTTPS. X-Real-IP should be set to $remote_addr to pass the client IP.

5fill in blank

hard

Fill all three blanks to set headers that forward the original host, protocol, and client IP to the backend.

Nginx

proxy_set_header Host [1];
proxy_set_header X-Forwarded-Proto [2];
proxy_set_header X-Real-IP [3];

Drag options to blanks, or click blank then click option'

A$remote_addr

B$scheme

C$host

D$server_name

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up $server_name and $host.

Using $remote_addr for Host header.

Using $host for X-Real-IP.

Set Host to $host to preserve the original host. Set X-Forwarded-Proto to $scheme to indicate the protocol. Set X-Real-IP to $remote_addr to forward the client IP.

Practice

1. What is the main purpose of setting proxy headers like X-Real-IP in an nginx configuration?

easy

A. To encrypt the data between nginx and the client

B. To cache the client's request on nginx

C. To pass the original client's IP address to the backend server

D. To block unwanted IP addresses from accessing the server

Solution

1. Step 1: Understand proxy headers role

   Proxy headers like X-Real-IP carry client info through nginx to backend servers.

2. Step 2: Identify the purpose of X-Real-IP

   This header specifically passes the original client's IP address to the backend for logging or processing.

3. Final Answer:

   To pass the original client's IP address to the backend server -> Option C

4. Quick Check:

   Proxy headers pass client info = B [OK]

Hint: Remember: X-Real-IP shows client's real IP to backend [OK]

Common Mistakes:

• Confusing proxy headers with encryption settings
• Thinking proxy headers cache requests
• Assuming proxy headers block IPs

2. Which of the following is the correct nginx directive to set the X-Forwarded-Proto header to the client's protocol?

easy

A. proxy_set_header X-Forwarded-Proto $scheme;

B. set_header X-Forwarded-Proto $protocol;

C. proxy_header X-Forwarded-Proto $scheme;

D. header_set X-Forwarded-Proto $protocol;

Solution

1. Step 1: Recall nginx syntax for proxy headers

   The correct directive to set headers in nginx proxy is proxy_set_header.

2. Step 2: Match variable for client protocol

   The variable $scheme holds the client's protocol (http or https).

3. Final Answer:

   proxy_set_header X-Forwarded-Proto $scheme; -> Option A

4. Quick Check:

   proxy_set_header + $scheme = A [OK]

Hint: Use proxy_set_header with $scheme for protocol header [OK]

Common Mistakes:

• Using incorrect directive names like set_header
• Using wrong variable names like $protocol
• Mixing directive order or syntax

3. Given this nginx proxy configuration snippet:

proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;

What will be the value of X-Forwarded-For if the client IP is 10.0.0.1 and the request passed through one proxy with IP 192.168.1.1?

medium

A. 10.0.0.1

B. 192.168.1.1, 10.0.0.1

C. 192.168.1.1

D. 10.0.0.1, 192.168.1.1

Solution

1. Step 1: Understand $proxy_add_x_forwarded_for behavior

   This variable appends the $remote_addr (proxy IP seen by nginx) to the existing X-Forwarded-For header chain from previous proxies.

2. Step 2: Order of IPs in X-Forwarded-For

   The chain lists the original client first, then proxy IPs appended. For client 10.0.0.1 via proxy 192.168.1.1, it becomes 10.0.0.1, 192.168.1.1.

3. Final Answer:

   10.0.0.1, 192.168.1.1 -> Option D

4. Quick Check:

   Client IP last in X-Forwarded-For = C [OK]

Hint: X-Forwarded-For lists original client first, then proxies [OK]

Common Mistakes:

• Reversing IP order in X-Forwarded-For
• Confusing X-Real-IP with X-Forwarded-For
• Ignoring existing proxy IPs in header

4. You have this nginx config snippet:

proxy_set_header X-Real-IP $remote_addr
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;

When reloading nginx, it fails with a syntax error. What is the problem?

medium

A. Missing semicolon at the end of the first proxy_set_header line

B. Incorrect variable name $proxy_add_x_forwarded_for

C. proxy_set_header cannot be used twice in one block

D. X-Real-IP header cannot be set manually

Solution

1. Step 1: Check nginx directive syntax

   Each directive line must end with a semicolon in nginx configuration.

2. Step 2: Identify missing semicolon

   The first line lacks a semicolon after $remote_addr, causing syntax error.

3. Final Answer:

   Missing semicolon at the end of the first proxy_set_header line -> Option A

4. Quick Check:

   Every directive needs semicolon = D [OK]

Hint: Always end nginx directives with semicolon [OK]

Common Mistakes:

• Ignoring semicolon syntax rules
• Assuming variable names are wrong without checking
• Thinking headers can't be set multiple times

5. You want to ensure your backend server correctly logs the original client IP and protocol when nginx proxies requests. Which complete nginx proxy header configuration snippet achieves this?

hard

A. proxy_set_header X-Real-IP $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Proto $protocol;

B. proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;

C. proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Real-IP $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;

D. proxy_set_header X-Real-IP $remote_addr
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for
proxy_set_header X-Forwarded-Proto $scheme

Solution

1. Step 1: Verify correct variables for headers

   X-Real-IP should be $remote_addr, X-Forwarded-For uses $proxy_add_x_forwarded_for, and X-Forwarded-Proto uses $scheme.

2. Step 2: Check syntax correctness

   Each directive must end with a semicolon; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header X-Forwarded-Proto $scheme; has correct syntax and variables.

3. Final Answer:

   proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header X-Forwarded-Proto $scheme; -> Option B

4. Quick Check:

   Correct vars + semicolons = A [OK]

Hint: Use $remote_addr, $proxy_add_x_forwarded_for, $scheme with semicolons [OK]

Common Mistakes:

• Swapping variables between headers
• Omitting semicolons causing errors
• Using undefined variables like $protocol