Location blocks in Nginx - Step-by-Step Execution

Process Flow - Location blocks

Request comes in

↓

Check location blocks in order

↓

Match exact location?

Yes→Use exact block

No↓

Match prefix location?

Yes→Use longest prefix block

No↓

Match regex location?

Yes→Use first regex match

No↓

Use default location block

↓

Serve request with chosen block

Nginx checks location blocks in a specific order: exact match first, then prefix matches, then regex matches, and finally the default block if no match is found.

Execution Sample

Nginx

location = /exact {
  return 200 'Exact match';
}

location /prefix {
  return 200 'Prefix match';
}

location ~ ^/regex {
  return 200 'Regex match';
}

This config defines three location blocks: exact match for /exact, prefix match for /prefix, and regex match for URLs starting with /regex.

Process Table

Step	Request URL	Check	Match Result	Chosen Location Block	Action
1	/exact	Check exact match location = /exact	Matched	/exact	Return 200 'Exact match'
2	/prefix/test	Check exact match location = /prefix/test	No match	N/A	Continue
3	/prefix/test	Check prefix location /prefix	Matched (longest prefix)	/prefix	Return 200 'Prefix match'
4	/regex123	Check exact match location = /regex123	No match	N/A	Continue
5	/regex123	Check prefix location /regex123	No match	N/A	Continue
6	/regex123	Check regex location ~ ^/regex	Matched	/regex	Return 200 'Regex match'
7	/other	Check exact match location = /other	No match	N/A	Continue
8	/other	Check prefix location /other	No match	N/A	Continue
9	/other	Check regex location ~ ^/regex	No match	N/A	Continue
10	/other	Use default location block	Default	/	Serve default content

💡 Request served by the first matching location block found in the order: exact, prefix, regex, or default.

Status Tracker

Variable	Start	After Step 1	After Step 3	After Step 6	After Step 10
Chosen Location Block	None	/exact	/prefix	/regex	/

Key Moments - 3 Insights

Why does nginx choose the exact match location block before prefix or regex?

Nginx prioritizes exact matches first as shown in execution_table row 1, so if an exact match exists, it uses that block immediately.

What happens if no exact or prefix location matches but a regex matches?

Nginx then uses the first regex location that matches, as seen in execution_table row 6 where regex match is chosen after no exact or prefix match.

Why is there a default location block used at the end?

If no exact, prefix, or regex matches are found, nginx falls back to the default location block to serve the request, as in execution_table row 10.

Visual Quiz - 3 Questions

Look at the execution table, which location block is chosen for the URL '/prefix/test'?

A /prefix

B /regex

C /exact

D /

💡 Hint

Check execution_table row 3 where prefix match is found for '/prefix/test'.

At which step does nginx decide to use the regex location block?

A Step 1

B Step 3

C Step 6

D Step 10

💡 Hint

See execution_table row 6 where regex match is confirmed.

If the exact location block for '/exact' was removed, what would happen for the URL '/exact'?

A Use regex location if matches

B Use prefix location if matches

C Use default location block

D Return 404 error

💡 Hint

Refer to concept_flow and execution_table logic: exact match missing leads to prefix match check.

Concept Snapshot

Nginx Location Blocks:
- Exact match (=) checked first
- Then longest prefix match (/)
- Then regex (~ or ~*) matches
- Finally default location (/)
Request served by first matching block found in this order.

Full Transcript

When nginx receives a request, it looks for a matching location block to decide how to serve it. It first checks if there is an exact match location block for the request URL. If found, it uses that block immediately. If not, it looks for prefix matches and chooses the longest matching prefix. If no prefix matches, it checks regex location blocks in order and uses the first regex that matches. If none of these match, it falls back to the default location block. This order ensures nginx serves requests efficiently and predictably.

Practice

1. What is the main purpose of a location block in an nginx configuration?

easy

A. To specify the server's hostname

B. To set the server's IP address

C. To define how nginx handles requests for specific URL paths

D. To configure the database connection

Solution

1. Step 1: Understand the role of location blocks

   Location blocks in nginx specify rules for handling requests based on URL paths.

2. Step 2: Compare options with location block purpose

   Only To define how nginx handles requests for specific URL paths correctly describes this purpose; others relate to different server settings.

3. Final Answer:

   To define how nginx handles requests for specific URL paths -> Option C

4. Quick Check:

   Location blocks control URL handling = D [OK]

Hint: Location blocks match URLs to control request handling [OK]

Common Mistakes:

• Confusing location blocks with server settings
• Thinking location blocks set server IP or hostname
• Mixing location blocks with database configs

2. Which of the following is the correct syntax to define a location block that matches the exact URL /about?

easy

A. location /about { }

B. location ~ /about { }

C. location ^~ /about { }

D. location = /about { }

Solution

1. Step 1: Understand location modifiers

   The = modifier matches the exact URL path.

2. Step 2: Match syntax to exact URL

   location = /about { } uses = /about which matches exactly '/about'. Others match prefixes or regex.

3. Final Answer:

   location = /about { } -> Option D

4. Quick Check:

   Exact match uses '=' modifier = C [OK]

Hint: Use '=' for exact URL match in location block [OK]

Common Mistakes:

• Using no modifier for exact match
• Confusing regex (~) with exact match
• Using ^~ which is prefix, not exact

3. Given this nginx config snippet:

location /images/ {
  root /data;
}

What is the full file path nginx will serve for a request to /images/pic.jpg?

medium

A. /data/pic.jpg

B. /data/images/pic.jpg

C. /images/pic.jpg

D. /data/images/

Solution

1. Step 1: Understand root directive with location

   The root directive appends the part of the URI after the location prefix to the root path.

2. Step 2: Combine root and URI

   Location prefix is /images/, request URI is /images/pic.jpg, so the part after prefix is pic.jpg. Root is /data, so full path is /data/pic.jpg.

3. Final Answer:

   /data/pic.jpg -> Option A

4. Quick Check:

   root + URI after location prefix = /data/pic.jpg [OK]

Hint: root + URI after location prefix = file path served [OK]

Common Mistakes:

• Assuming root combines with full URI
• Using full URI instead of URI after location prefix
• Confusing alias with root behavior

4. Identify the error in this nginx location block:

location /static/ {
  alias /var/www/static;
}

medium

A. Missing trailing slash in alias path

B. alias should be root here

C. location path should not end with slash

D. No error, configuration is correct

Solution

1. Step 1: Understand alias usage

   When using alias with a location ending with a slash, the alias path must also end with a slash.

2. Step 2: Check alias path

   Alias path /var/www/static lacks trailing slash, causing incorrect file path resolution.

3. Final Answer:

   Missing trailing slash in alias path -> Option A

4. Quick Check:

   Alias path must end with '/' if location ends with '/' = B [OK]

Hint: Alias path needs trailing slash if location ends with slash [OK]

Common Mistakes:

• Using root instead of alias incorrectly
• Omitting trailing slash on alias path
• Thinking location path cannot end with slash

5. You want nginx to serve static files from /var/www/app/static when users request URLs starting with /static/, but you want to avoid duplicating the /static/ part in the file path. Which location block correctly achieves this?

hard

A. location /static/ { root /var/www/app/static; }

B. location /static/ { alias /var/www/app/static/; }

C. location /static/ { alias /var/www/app/static; }

D. location /static/ { root /var/www/app; }

Solution

1. Step 1: Understand alias vs root behavior

   Alias replaces the location prefix with the alias path exactly, avoiding duplication.

2. Step 2: Check trailing slashes for alias

   Alias path must end with a slash to match location ending with slash, ensuring correct path mapping.

3. Step 3: Evaluate options

   location /static/ { alias /var/www/app/static/; } uses alias with trailing slash, correctly mapping /static/file to /var/www/app/static/file. Others either duplicate path or miss slash.

4. Final Answer:

   location /static/ { alias /var/www/app/static/; } -> Option B

5. Quick Check:

   Alias with trailing slash avoids duplication = A [OK]

Hint: Use alias with trailing slash to avoid path duplication [OK]

Common Mistakes:

• Using root causing duplicated /static/ in path
• Omitting trailing slash on alias path
• Confusing alias and root usage