Prefix match in Nginx - Mini Project: Build & Apply

Prefix Match in Nginx Configuration

📖 Scenario: You are setting up a simple web server using Nginx. You want to serve different content based on the URL path prefix.For example, requests starting with /images should serve image files, and requests starting with /videos should serve video files.

🎯 Goal: Configure Nginx to use prefix matching in location blocks to serve different content based on URL path prefixes.

📋 What You'll Learn

Create an Nginx configuration file with a server block

Add a location block that matches the prefix /images

Add a location block that matches the prefix /videos

Set the root directory for each prefix to /var/www/images and /var/www/videos respectively

Print the final Nginx configuration

💡 Why This Matters

🌍 Real World

Web servers often serve different types of content from different folders. Using prefix matching in Nginx helps route requests to the right content folder.

💼 Career

Understanding Nginx configuration and prefix matching is essential for DevOps roles managing web servers and deploying web applications.

1

Create the basic Nginx server block

Create a variable called nginx_config and assign it a string containing the basic Nginx server block with listen 80; and an empty body for server.

Nginx

# Your code here

Hint

Start with a string that contains server { and listen 80; lines.

2

Add a location block for the /images prefix

Add a location /images/ block inside the server block in nginx_config string. Set its alias to /var/www/images/. Use string concatenation or multiline string to add this block.

Nginx

nginx_config = "server {\n    listen 80;\n}\n"
# Add location block for /images prefix here

Hint

Inside the server block, add location /images/ { alias /var/www/images/; }.

3

Add a location block for the /videos prefix

Add a location /videos/ block inside the server block in nginx_config string. Set its alias to /var/www/videos/. Append this block after the /images block.

Nginx

nginx_config = "server {\n    listen 80;\n    location /images/ {\n        alias /var/www/images/;\n    }\n}\n"
# Add location block for /videos prefix here

Hint

Append location /videos/ { alias /var/www/videos/; } inside the server block.

4

Print the final Nginx configuration

Write a print statement to display the content of nginx_config.

Nginx

nginx_config = "server {\n    listen 80;\n    location /images/ {\n        alias /var/www/images/;\n    }\n    location /videos/ {\n        alias /var/www/videos/;\n    }\n}\n"
# Print the nginx_config variable below

Hint

Use print(nginx_config) to show the full configuration.

Practice

1. What does prefix match in nginx do when routing requests?

easy

A. It matches requests based on the start of the URL path.

B. It matches requests only if the full URL matches exactly.

C. It matches requests based on the file extension.

D. It matches requests randomly to any location block.

Solution

1. Step 1: Understand prefix match concept

   Prefix match means nginx checks if the URL path starts with a specific string.

2. Step 2: Compare with other matching types

   Exact match requires full URL match, file extension match is unrelated, random match is invalid.

3. Final Answer:

   It matches requests based on the start of the URL path. -> Option A

4. Quick Check:

   Prefix match = start of URL path [OK]

Hint: Prefix match checks URL start, not full or random [OK]

Common Mistakes:

• Confusing prefix match with exact match
• Thinking prefix match checks file extensions
• Assuming prefix match is random

2. Which of the following is the correct syntax for a prefix match location in nginx?

easy

A. location = /images/ { }

B. location ^~ /images/ { }

C. location /images/ { }

D. location ~ /images/ { }

Solution

1. Step 1: Identify prefix match syntax

   Prefix match uses plain location /prefix/ { } without modifiers.

2. Step 2: Understand other modifiers

   = is exact match, ^~ is prefix but with higher priority, ~ is regex match.

3. Final Answer:

   location /images/ { } -> Option C

4. Quick Check:

   Plain location = prefix match [OK]

Hint: Plain location block means prefix match [OK]

Common Mistakes:

• Using = or ^~ modifiers for simple prefix match
• Confusing regex (~) with prefix match
• Missing trailing slash in prefix

3. Given this nginx config snippet:

location /app/ {
  proxy_pass http://backend1;
}
location /app/api/ {
  proxy_pass http://backend2;
}

Which backend will handle a request to /app/api/users?

medium

A. Both backends in round-robin

B. http://backend2

C. No backend, 404 error

D. http://backend1

Solution

1. Step 1: Understand prefix match selection

   nginx selects the location with the longest matching prefix for plain prefix locations (no modifiers).

2. Step 2: Compare prefixes

   Both /app/ (length 5) and /app/api/ (length 9) match /app/api/users, but /app/api/ is longer, so it wins.

3. Final Answer:

   http://backend2 -> Option B

4. Quick Check:

   Longest prefix wins [OK]

Hint: Longest matching prefix wins [OK]

Common Mistakes:

• Thinking config order (first match) wins instead of longest prefix
• Thinking regex or exact match applies here
• Believing nginx load balances both backends

4. You wrote this nginx config:

location /static {
  root /var/www/html;
}

Requests to /static/css/style.css return 404. What is the likely error?

medium

A. root directive path is incorrect

B. location block should use = modifier

C. Missing trailing slash in location prefix

D. proxy_pass is missing

Solution

1. Step 1: Understand root directive behavior

   root appends the full request URI (/static/css/style.css) to /var/www/html, looking for /var/www/html/static/css/style.css.

2. Step 2: Identify likely cause

   If static files are at /var/www/html/css/style.css (without static/), root path doesn't strip prefix, causing 404. (Use alias /var/www/html; to strip.)

3. Final Answer:

   root directive path is incorrect -> Option A

4. Quick Check:

   root + full URI (no prefix strip) [OK]

Hint: root appends full URI; alias strips prefix [OK]

Common Mistakes:

• Confusing root (full URI) with alias (strips prefix)
• Thinking trailing slash strips prefix for root
• Adding unnecessary modifiers like =

5. You want nginx to route all requests starting with /api/ to http://backend_api and all others to http://backend_web, ensuring the /api/ prefix has priority even if regex locations follow. Which config correctly uses prefix match for this?

hard

A. location ~ /api/ {
proxy_pass http://backend_api;
}
location / {
proxy_pass http://backend_web;
}

B. location /api/ {
proxy_pass http://backend_api;
}
location / {
proxy_pass http://backend_web;
}

C. location = /api/ {
proxy_pass http://backend_api;
}
location / {
proxy_pass http://backend_web;
}

D. location ^~ /api/ {
proxy_pass http://backend_api;
}
location / {
proxy_pass http://backend_web;
}

Solution

1. Step 1: Use ^~ for prefix priority

   The ^~ modifier tells nginx to stop searching if prefix matches, ensuring /api/ routes to backend_api even over later regex.

2. Step 2: Default location for others

   The plain location / { } catches all other requests to backend_web.

3. Final Answer:

   location ^~ /api/ { proxy_pass http://backend_api; } location / { proxy_pass http://backend_web; } -> Option D

4. Quick Check:

   ^~ prefix match for priority routing [OK]

Hint: Use ^~ to prioritize prefix match over regex [OK]

Common Mistakes:

• Not using ^~ causes regex or exact match to override
• Using = modifier limits to exact /api/ only
• Using ~ makes it regex, not prefix match