Index directive in Nginx - Step-by-Step Execution

Process Flow - Index directive

Client requests URL

↓

Check if URL is directory

Yes↓

Look for index files in order

↓

Serve index file

No↓

Return directory listing or error

When a client requests a directory URL, nginx checks for index files in the order specified by the index directive and serves the first one found.

Execution Sample

Nginx

location / {
    index index.html index.htm index.php;
}

This configuration tells nginx to look for index.html first, then index.htm, then index.php when a directory is requested.

Process Table

Step	Action	Index Files Checked	File Found	Result
1	Client requests /about/	index.html	No	Check next index file
2	Check index.htm	index.htm	No	Check next index file
3	Check index.php	index.php	Yes	Serve index.php file
4	End	-	-	Request served with index.php

💡 index.php found, so nginx serves this file and stops checking further.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
Current Index File	index.html	index.htm	index.php	index.php	index.php
File Found	No	No	Yes	Yes	Yes

Key Moments - 2 Insights

Why does nginx check multiple index files instead of just one?

Because the index directive lists files in order, nginx tries each until it finds one that exists, as shown in execution_table steps 1 to 3.

What happens if none of the index files exist?

Nginx will either show a directory listing or return an error, but this is not shown in the current execution because index.php was found at step 3.

Visual Quiz - 3 Questions

Look at the execution_table, which index file is served to the client?

A index.php

B index.htm

C index.html

D No index file served

💡 Hint

Check the 'File Found' and 'Result' columns in execution_table row 3.

At which step does nginx stop checking further index files?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at when 'File Found' changes to Yes in variable_tracker and execution_table.

If index.html existed, how would the execution_table change?

A Nginx would serve index.php anyway.

B Nginx would still check all files before serving.

C Nginx would serve index.html at step 1 and stop checking.

D Nginx would return an error.

💡 Hint

Index directive order means nginx serves the first found file, see concept_flow.

Concept Snapshot

Index directive syntax:
index file1 file2 file3;
When a directory URL is requested,
nginx checks these files in order.
It serves the first existing file found.
If none found, shows listing or error.

Full Transcript

The index directive in nginx specifies a list of files to look for when a client requests a directory URL. Nginx checks each file in the order listed until it finds one that exists. Then it serves that file. If no files are found, nginx may show a directory listing or an error. In the example, nginx checks index.html, then index.htm, then index.php. It finds index.php and serves it, stopping further checks. This process ensures the correct default file is served for directory requests.

Practice

1.

What is the main purpose of the index directive in nginx?

easy

A. To specify default files to serve when a directory is requested

B. To set the server's IP address

C. To configure SSL certificates

D. To define error pages

Solution

1. Step 1: Understand the role of the index directive

   The index directive tells nginx which files to look for by default when a user requests a directory URL.

2. Step 2: Match the purpose with the options

   Only To specify default files to serve when a directory is requested describes setting default files to serve in a folder, which matches the index directive's function.

3. Final Answer:

   To specify default files to serve when a directory is requested -> Option A

4. Quick Check:

   index directive = default files [OK]

Hint: Index sets default homepage files for folders [OK]

Common Mistakes:

• Confusing index with server IP settings
• Thinking index sets error pages
• Mixing index with SSL configuration

2.

Which of the following is the correct syntax to set index.html and home.html as default files using the index directive?

?

easy

A. index: index.html; home.html;

B. index = index.html, home.html;

C. index { index.html home.html }

D. index index.html home.html;

Solution

1. Step 1: Recall nginx index directive syntax

   The correct syntax lists files separated by spaces, ending with a semicolon.

2. Step 2: Compare options with correct syntax

   index index.html home.html; matches the correct syntax: index index.html home.html;. Others use invalid punctuation or braces.

3. Final Answer:

   index index.html home.html; -> Option D

4. Quick Check:

   Correct syntax = index index.html home.html; [OK]

Hint: List files with spaces, end with semicolon [OK]

Common Mistakes:

• Using commas between filenames
• Using braces or colons incorrectly
• Adding equal signs in directive

3.

Given this nginx config snippet:

location / {
    index about.html index.html;
}

If the folder contains index.html but not about.html, which file will nginx serve when a user visits /?

medium

A. 404 Not Found error

B. about.html

C. index.html

D. Directory listing

Solution

1. Step 1: Understand index file priority

   nginx tries files in order: first about.html, then index.html.

2. Step 2: Check which files exist

   about.html is missing, but index.html exists, so nginx serves index.html.

3. Final Answer:

   index.html -> Option C

4. Quick Check:

   First found file served = index.html [OK]

Hint: nginx serves first existing file in index list [OK]

Common Mistakes:

• Assuming nginx serves first listed file regardless of existence
• Expecting directory listing if first file missing
• Thinking nginx returns error immediately

4.

Identify the error in this nginx config snippet:

location / {
    index index.html, home.html;
}

medium

A. Missing semicolon at the end

B. Using a comma between filenames is invalid syntax

C. index directive cannot be used inside location block

D. File names must be in quotes

Solution

1. Step 1: Check syntax for index directive

   File names must be separated by spaces, not commas.

2. Step 2: Identify the error in the snippet

   The comma between index.html and home.html is invalid syntax.

3. Final Answer:

   Using a comma between filenames is invalid syntax -> Option B

4. Quick Check:

   No commas allowed in index list [OK]

Hint: Separate files with spaces, no commas [OK]

Common Mistakes:

• Adding commas between filenames
• Omitting semicolon
• Thinking quotes are required

5.

You want nginx to serve main.html as the default file, but only if index.html is missing. Which index directive correctly achieves this?

hard

A. index index.html main.html;

B. index main.html index.html;

C. index main.html;

D. index index.html;

Solution

1. Step 1: Understand index file priority order

   nginx serves the first existing file in the list from left to right.

2. Step 2: Choose order to serve main.html only if index.html missing

   To serve main.html only if index.html is missing, index.html must be first, then main.html.

3. Final Answer:

   index index.html main.html; -> Option A

4. Quick Check:

   First existing file served = index.html then main.html [OK]

Hint: List index.html first to prefer it over main.html [OK]

Common Mistakes:

• Reversing file order
• Listing only one file
• Expecting nginx to skip files in order