Adding response headers (add_header) in Nginx - Commands & Configuration

Introduction

Sometimes websites need to send extra information to browsers or clients. Adding response headers lets you include this extra info in the server's reply. This helps with security, caching, or telling browsers how to behave.

When you want to improve security by adding headers like Content-Security-Policy or X-Frame-Options.

When you want to control browser caching by adding Cache-Control headers.

When you want to add custom headers to track or identify responses.

When you want to enable CORS by adding Access-Control-Allow-Origin headers.

When you want to add headers that tell browsers to upgrade insecure requests.

Config File - nginx.conf

nginx.conf

events {}

http {
    server {
        listen 8080;
        server_name localhost;

        location / {
            root /usr/share/nginx/html;
            index index.html;

            add_header X-Content-Type-Options "nosniff";
            add_header X-Frame-Options "DENY";
            add_header Cache-Control "no-store, no-cache, must-revalidate, proxy-revalidate, max-age=0";
        }
    }
}

This configuration sets up a simple server listening on port 8080.

The add_header directives inside the location / block add three response headers:

• X-Content-Type-Options nosniff: prevents browsers from guessing the content type.
• X-Frame-Options DENY: stops the page from being shown in frames to prevent clickjacking.
• Cache-Control: disables caching to always get fresh content.

Commands

This command tests the nginx configuration file for syntax errors before applying changes.

Terminal

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

This command reloads nginx to apply the new configuration without stopping the server.

Terminal

systemctl reload nginx

Expected Output

No output (command runs silently)

This command requests only the headers from the server to verify the added response headers.

Terminal

curl -I http://localhost:8080

Expected Output

HTTP/1.1 200 OK

Server: nginx/1.24.0

Date: Thu, 01 Jun 2024 12:00:00 GMT

Content-Type: text/html

Content-Length: 612

Last-Modified: Wed, 31 May 2024 10:00:00 GMT

Connection: keep-alive

X-Content-Type-Options: nosniff

X-Frame-Options: DENY

Cache-Control: no-store, no-cache, must-revalidate, proxy-revalidate, max-age=0

Key Concept

If you remember nothing else from this pattern, remember: add_header lets you send extra info in server replies to control browser behavior and improve security.

Common Mistakes

Placing add_header directives outside the http, server, or location blocks.

Nginx ignores add_header if it is not inside a valid context, so headers won't be added.

Always put add_header inside http, server, or location blocks where it applies.

Not reloading nginx after changing the configuration.

Changes won't take effect until nginx reloads or restarts.

Run 'systemctl reload nginx' or 'nginx -s reload' after editing config.

Using add_header with variables or conditions without proper syntax.

Older nginx versions ignore add_header with variables; headers won't appear.

Use nginx 1.7.5 or newer and proper syntax for conditional headers.

Summary

Use add_header inside server or location blocks to add custom response headers.

Test your nginx config with 'nginx -t' before reloading to avoid errors.

Reload nginx to apply changes and verify headers with 'curl -I'.

Practice

1. What is the main purpose of the add_header directive in nginx?

easy

A. To configure server listening ports

B. To add extra information to HTTP responses

C. To redirect HTTP requests to HTTPS

D. To define server root directory

Solution

1. Step 1: Understand the role of add_header

   The add_header directive is used to add extra HTTP headers to responses sent by nginx.

2. Step 2: Compare with other options

   Redirecting requests, configuring ports, and defining root directories are unrelated to adding headers.

3. Final Answer:

   To add extra information to HTTP responses -> Option B

4. Quick Check:

   add_header adds headers [OK]

Hint: Remember: add_header adds info to HTTP responses [OK]

Common Mistakes:

• Confusing add_header with redirect directives
• Thinking add_header sets server ports
• Assuming add_header changes root directory

2. Which of the following is the correct syntax to add a custom header named X-Custom-Header with value MyValue in nginx?

easy

A. add_header "X-Custom-Header: MyValue";

B. add_header X-Custom-Header = MyValue;

C. add_header X-Custom-Header MyValue;

D. add_header X-Custom-Header => MyValue;

Solution

1. Step 1: Recall nginx add_header syntax

   The correct syntax is add_header name value; without extra symbols like = or =>.

2. Step 2: Validate each option

   add_header X-Custom-Header MyValue; matches correct syntax. Options A, C, and D use invalid syntax with quotes or symbols.

3. Final Answer:

   add_header X-Custom-Header MyValue; -> Option C

4. Quick Check:

   Syntax is add_header name value; [OK]

Hint: Use simple syntax: add_header name value; [OK]

Common Mistakes:

• Adding quotes around header name and value
• Using = or => symbols incorrectly
• Missing semicolon at the end

3. Given this nginx config snippet inside a server block:

add_header X-Test "Hello";

location /error {
  return 404;
}

What happens when a client requests /error?

medium

A. The server throws a configuration error

B. The response includes header X-Test: Hello with 404 status

C. The response returns 200 OK with X-Test header

D. The response returns 404 without X-Test header

Solution

1. Step 1: Understand default add_header behavior on errors

   By default, add_header does NOT add headers on error responses like 404.

2. Step 2: Analyze the config and request

   The location returns 404, so X-Test header is omitted unless always is used.

3. Final Answer:

   The response returns 404 without X-Test header -> Option D

4. Quick Check:

   Headers not added on errors without always [OK]

Hint: Headers need 'always' to appear on error responses [OK]

Common Mistakes:

• Assuming headers always appear on error responses
• Confusing return status with header presence
• Expecting 200 OK instead of 404

4. You want to add a security header X-Frame-Options: DENY to all responses including errors. Which nginx config fixes this incorrect snippet?

add_header X-Frame-Options DENY;

But headers are missing on 404 pages.

medium

A. Change to add_header X-Frame-Options DENY always;

B. Add always; on a separate line

C. Use add_header X-Frame-Options DENY on_error;

D. Move add_header inside error_page block

Solution

1. Step 1: Identify why headers are missing on errors

   By default, add_header skips error responses unless always is added.

2. Step 2: Fix syntax to include headers on all responses

   Adding always on the same line ensures headers appear even on errors.

3. Final Answer:

   Change to add_header X-Frame-Options DENY always; -> Option A

4. Quick Check:

   Use 'always' on same line to add headers on errors [OK]

Hint: Add 'always' on same line to include headers on errors [OK]

Common Mistakes:

• Placing 'always' on a separate line
• Using invalid keywords like 'on_error'
• Moving add_header inside unrelated blocks

5. You want to add two headers: Cache-Control: no-store for all responses, and Strict-Transport-Security: max-age=31536000 only for successful responses (status 200-299). Which nginx config achieves this correctly?

hard

A. add_header Cache-Control no-store always;
add_header Strict-Transport-Security max-age=31536000;

B. add_header Cache-Control no-store;
add_header Strict-Transport-Security max-age=31536000 always;

C. add_header Cache-Control no-store;
add_header Strict-Transport-Security max-age=31536000;

D. add_header Cache-Control no-store always;
add_header Strict-Transport-Security max-age=31536000 always;

Solution

1. Step 1: Understand 'always' effect on headers

   The always flag makes headers appear on all responses including errors.

2. Step 2: Apply 'always' only to Cache-Control

   We want Cache-Control on all responses, so add always there. For Strict-Transport-Security, omit always to restrict to 2xx responses.

3. Final Answer:

   add_header Cache-Control no-store always; add_header Strict-Transport-Security max-age=31536000; -> Option A

4. Quick Check:

   'always' for all responses, omit for success-only [OK]

Hint: Use 'always' only for headers needed on errors [OK]

Common Mistakes:

• Adding 'always' to all headers causing unwanted error headers
• Omitting 'always' for headers needed on errors
• Misunderstanding which responses get headers without 'always'