Nested location blocks in Nginx - Step-by-Step Execution

Process Flow - Nested location blocks

Request comes in

↓

Match outer location block

Yes↓

Check nested location blocks

Yes↓

Match most specific nested location

↓

Serve content or proxy

↓

End

When a request arrives, nginx first matches the outer location block, then checks nested locations inside it to find the most specific match before serving content.

Execution Sample

Nginx

server {
  location /app/ {
    root /var/www/html;
    location /app/images/ {
      root /var/www/images;
    }
  }
}

This config shows a nested location where /app/images/ overrides the root for image files inside /app.

Process Table

Step	Request URI	Outer Location Match	Nested Location Check	Nested Location Match	Action Taken
1	/app/index.html	/app/ matches	Check nested locations	No nested match	Serve /var/www/html/app/index.html
2	/app/images/logo.png	/app/ matches	Check nested locations	/app/images/ matches	Serve /var/www/images/app/images/logo.png
3	/app/css/style.css	/app/ matches	Check nested locations	No nested match	Serve /var/www/html/app/css/style.css
4	/other/page.html	No outer match	No nested check	No nested match	No match, default server action

💡 Execution stops after serving matched content or default action if no location matches.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4
Request URI		/app/index.html	/app/images/logo.png	/app/css/style.css	/other/page.html
Outer Location	none	/app/	/app/	/app/	none
Nested Location	none	none	/app/images/	none	none
Root Used	none	/var/www/html	/var/www/images	/var/www/html	default

Key Moments - 2 Insights

Why does /app/images/logo.png use a different root than /app/index.html?

Because /app/images/ is a nested location inside /app/ with its own root directive, nginx uses the nested location's root for more specific matches as shown in step 2 of the execution_table.

What happens if a request does not match the outer location block?

Nginx skips nested location checks and uses the default server action, as shown in step 4 where /other/page.html does not match any location.

Visual Quiz - 3 Questions

Look at the execution table, what root is used for the request /app/css/style.css?

A /var/www/images

B /var/www/html

C default root

D No root used

💡 Hint

Check step 3 in the execution_table under 'Root Used' column.

At which step does nginx find a nested location match?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Nested Location Match' column in the execution_table.

If the nested location /app/images/ was removed, what would happen to requests for /app/images/logo.png?

A They would use /var/www/html root

B They would use /var/www/images root

C They would not match any location

D They would cause an error

💡 Hint

Refer to the variable_tracker and execution_table for how nested locations override outer roots.

Concept Snapshot

Nested location blocks in nginx allow more specific matching inside a broader location.
Nginx first matches the outer location, then checks nested locations.
The most specific nested location's settings override outer ones.
If no nested match, outer location settings apply.
Requests not matching outer location skip nested checks.
Use nested locations to organize and override config cleanly.

Full Transcript

When nginx receives a request, it first tries to match the outer location block. If it finds one, it then checks if any nested location blocks inside it match the request more specifically. If a nested location matches, nginx uses its configuration, such as root or proxy settings, to serve the request. If no nested location matches, nginx uses the outer location's settings. If the request does not match the outer location at all, nginx skips nested checks and uses the default server behavior. For example, a request to /app/images/logo.png matches the outer /app/ location and the nested /app/images/ location, so nginx uses the nested root /var/www/images. A request to /app/index.html matches only the outer location, so it uses /var/www/html. This layered matching helps organize configurations clearly and apply specific rules where needed.

Practice

1. What is the main purpose of using nested location blocks in an nginx configuration?

easy

A. To automatically update nginx software

B. To increase server hardware performance

C. To organize URL handling inside parent paths for clearer rules

D. To disable logging for specific URLs

Solution

1. Step 1: Understand the role of location blocks

   Location blocks define how nginx handles requests for specific URL paths.

2. Step 2: Recognize the benefit of nesting

   Nested location blocks allow specific rules for sub-paths without repeating the parent path, making configuration clearer.

3. Final Answer:

   To organize URL handling inside parent paths for clearer rules -> Option C

4. Quick Check:

   Nested location blocks = organize URL handling [OK]

Hint: Nested blocks group URL rules under parent paths [OK]

Common Mistakes:

• Thinking nested blocks improve hardware speed
• Confusing nested blocks with software updates
• Assuming nested blocks disable logging

2. Which of the following is the correct syntax to define a nested location block inside location /app/ in nginx?

easy

A. location /app/ { location api/ { proxy_pass http://backend; } }

B. location /app/ { location /appapi/ { proxy_pass http://backend; } }

C. location /app/ { location /app/api/ { proxy_pass http://backend; } }

D. location /app/ { location /api/ { proxy_pass http://backend; } }

Solution

1. Step 1: Check nested location path relative to parent

   Nested location inside location /app/ should define sub-paths relative to /app/, so api/ without leading slash is correct.

2. Step 2: Validate syntax correctness

   location /app/ { location api/ { proxy_pass http://backend; } } uses location api/ inside location /app/, which is valid and clear.

3. Final Answer:

   location /app/ { location api/ { proxy_pass http://backend; } } -> Option A

4. Quick Check:

   Nested path is relative and omits leading slash [OK]

Hint: Nested location paths omit parent prefix and leading slash inside block [OK]

Common Mistakes:

• Repeating full parent path in nested location
• Missing leading slash in nested path
• Combining parent and child paths incorrectly

3. Given this nginx config snippet:

location /shop/ {
  root /var/www/html;
  location /cart/ {
    proxy_pass http://cart_backend;
  }
}

What happens when a user requests /shop/cart/view?

medium

A. Request serves static file /var/www/html/shop/cart/view

B. Request is proxied to http://cart_backend/view

C. Request returns 404 Not Found

D. Request is proxied to http://cart_backend/shop/cart/view

Solution

1. Step 1: Identify matching location block

   Request /shop/cart/view matches nested location /cart/ inside location /shop/.

2. Step 2: Understand proxy_pass behavior

   Proxy_pass inside nested block forwards request path after /cart/, so /view is sent to http://cart_backend.

3. Final Answer:

   Request is proxied to http://cart_backend/view -> Option B

4. Quick Check:

   Nested proxy_pass strips matched prefix [OK]

Hint: Nested proxy_pass forwards sub-path after nested location [OK]

Common Mistakes:

• Assuming static file serving instead of proxy
• Including full original path in proxy_pass
• Expecting 404 due to nested block

4. Identify the error in this nginx config snippet:

location /api/ {
  location /v1/ {
    proxy_pass http://api_v1_backend;
  }
  location /v2/ {
    proxy_pass http://api_v2_backend;
  }
}

medium

A. Nested location blocks cannot be used inside another location

B. No error; configuration is valid

C. proxy_pass URLs must include trailing slash

D. Nested location paths should not start with a slash

Solution

1. Step 1: Recall nested location path syntax

   Nested location paths inside a parent location should be relative and not start with a slash.

2. Step 2: Check given nested paths

   Nested locations use /v1/ and /v2/ starting with slash, which is incorrect.

3. Final Answer:

   Nested location paths should not start with a slash -> Option D

4. Quick Check:

   Nested paths omit leading slash [OK]

Hint: Nested location paths omit leading slash [OK]

Common Mistakes:

• Thinking nested locations are disallowed
• Believing proxy_pass must have trailing slash
• Assuming config is valid as is

5. You want to serve static files from /var/www/app for /app/ URLs, but proxy API requests under /app/api/ to http://api_backend. Which nested location block setup is correct?

hard

A. location /app/ { root /var/www/app; location api/ { proxy_pass http://api_backend; } }

B. location /app/ { root /var/www/app; location /api/ { proxy_pass http://api_backend; } }

C. location /app/ { root /var/www/app; location /app/api/ { proxy_pass http://api_backend; } }

D. location /app/ { root /var/www/app; location /appapi/ { proxy_pass http://api_backend; } }

Solution

1. Step 1: Set root for /app/ static files

   Use root /var/www/app; inside location /app/ to serve static files.

2. Step 2: Define nested location for API proxy

   Nested location for /app/api/ should be location api/ without leading slash inside location /app/.

3. Step 3: Verify proxy_pass target

   Proxy_pass points to http://api_backend correctly.

4. Final Answer:

   location /app/ { root /var/www/app; location api/ { proxy_pass http://api_backend; } } -> Option A

5. Quick Check:

   Nested path omits /, root set for static, proxy for api [OK]

Hint: Nested location paths omit leading slash; root applies to parent [OK]

Common Mistakes:

• Repeating full path in nested location
• Using leading slash in nested location
• Misplacing root directive inside nested block