Try_files directive in Nginx - Step-by-Step Execution

Process Flow - Try_files directive

Request comes in

↓

Try first file

↓

Serve file

No↓

Try second file

↓

Serve file

No↓

Fallback URI

↓

Serve fallback or error

The try_files directive checks files in order and serves the first existing one, or falls back to a URI if none exist.

Execution Sample

Nginx

location / {
  try_files $uri $uri/ /index.html;
}

This tries to serve the requested URI as a file, then as a directory, then falls back to /index.html.

Process Table

Step	Requested URI	File Checked	Exists?	Action
1	/about	/about	No	Try next file
2	/about	/about/	No	Try next file
3	/about	/index.html	Yes	Serve /index.html
4	END	-	-	Request served, stop

💡 Stopped after serving /index.html fallback because previous files did not exist.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
$uri	/about	/about	/about	/about	/about
File Checked	-	/about	/about/	/index.html	/index.html
Exists?	-	No	No	Yes	Yes
Action	-	Try next	Try next	Serve file	Serve file

Key Moments - 2 Insights

Why does nginx try multiple files instead of serving the first one it checks?

Because try_files checks each file in order and only serves the first one that exists. If a file doesn't exist, it moves to the next (see execution_table steps 1 and 2).

What happens if none of the files exist?

Nginx serves the fallback URI specified last in try_files, like /index.html in the example (see execution_table step 3).

Visual Quiz - 3 Questions

Look at the execution table, what file does nginx serve at step 3?

A /index.html

B /about/

C /about

D No file served

💡 Hint

Check the 'File Checked' and 'Action' columns at step 3 in the execution_table.

At which step does nginx find an existing file to serve?

A Step 1

B Step 3

C Step 2

D No step, it never finds a file

💡 Hint

Look at the 'Exists?' column in the execution_table to see when it becomes 'Yes'.

If /about existed as a file, how would the execution table change?

A Nginx would still check /about/ and /index.html

B Nginx would serve /index.html anyway

C Step 1 'Exists?' would be Yes and nginx would serve /about immediately

D The fallback URI would be served first

💡 Hint

Try_files stops at the first existing file, see execution_table step 1 for current behavior.

Concept Snapshot

try_files directive syntax:
try_files file1 file2 ... fallback_uri;

Checks each file in order.
Serves the first existing file.
If none exist, serves fallback URI.
Useful for clean URLs and SPA fallback.

Full Transcript

The try_files directive in nginx processes a request by checking a list of files in order. It tries to find the first file that exists on the server matching the requested URI or alternatives. If it finds one, it serves that file immediately. If none of the files exist, it serves a fallback URI, often used to serve a default page like index.html. This behavior helps handle requests for static files, directories, or fallback pages in a clean and efficient way.

Practice

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

easy

A. To check multiple files or paths in order and serve the first found

B. To restart the nginx server automatically

C. To define user permissions for files

D. To log errors in a custom file

Solution

1. Step 1: Understand the role of try_files

   The try_files directive checks a list of files or paths one by one.

2. Step 2: Identify its purpose

   It serves the first file found or falls back to a default if none exist.

3. Final Answer:

   To check multiple files or paths in order and serve the first found -> Option A

4. Quick Check:

   try_files = check files in order [OK]

Hint: Remember: try_files tries files one by one until success [OK]

Common Mistakes:

• Thinking try_files restarts nginx
• Confusing try_files with permission settings
• Assuming try_files logs errors

2. Which of the following is the correct syntax for the try_files directive in nginx?

easy

A. try_files file1 file2 fallback;

B. try_files file1 file2 =404;

C. try_files file1, file2, fallback;

D. try_files (file1 file2 fallback);

Solution

1. Step 1: Recall try_files syntax rules

   The try_files directive lists files separated by spaces, ending with a fallback like =404.

2. Step 2: Identify correct syntax

   try_files file1 file2 =404; uses spaces and ends with =404, which is valid syntax.

3. Final Answer:

   try_files file1 file2 =404; -> Option B

4. Quick Check:

   try_files syntax uses spaces and fallback [OK]

Hint: Use spaces, no commas or parentheses, end with fallback [OK]

Common Mistakes:

• Using commas between file names
• Adding parentheses around files
• Omitting fallback or using wrong fallback syntax

3. Given this nginx config snippet:

location / {
  try_files $uri $uri/ /index.html;
}

What happens when a user requests /about and /about is not a file but /about/ is a directory?

medium

A. nginx serves the /about file

B. nginx returns a 404 error

C. nginx serves the /about/ directory index

D. nginx serves /index.html fallback

Solution

1. Step 1: Understand try_files order

   nginx first checks if /about file exists, then /about/ directory.

2. Step 2: Apply to given request

   /about file is missing, but /about/ directory exists, so nginx serves the directory index.

3. Final Answer:

   nginx serves the /about/ directory index -> Option C

4. Quick Check:

   try_files checks files then directories [OK]

Hint: try_files checks files then directories in order [OK]

Common Mistakes:

• Assuming it serves /index.html fallback immediately
• Thinking it returns 404 if file missing
• Ignoring directory check after file check

4. Identify the error in this nginx config snippet:

location / {
  try_files $uri, $uri/, /fallback.html;
}

medium

A. Using commas between file names is invalid syntax

B. Missing semicolon at the end of try_files

C. Fallback file must be =404, not /fallback.html

D. Variables like $uri cannot be used in try_files

Solution

1. Step 1: Check try_files syntax

   try_files expects file names separated by spaces, not commas.

2. Step 2: Identify error in snippet

   The commas after $uri and $uri/ cause syntax error.

3. Final Answer:

   Using commas between file names is invalid syntax -> Option A

4. Quick Check:

   try_files uses spaces, no commas [OK]

Hint: No commas in try_files list, only spaces [OK]

Common Mistakes:

• Adding commas between file names
• Confusing fallback with error codes
• Thinking variables are disallowed in try_files

5. You want nginx to try serving /images/$uri, then /images/default.png if the first doesn't exist. Which try_files directive correctly implements this?

hard

A. try_files /images/$uri /images/default.png /index.html;

B. try_files $uri /images/default.png;

C. try_files /images/$uri /images/default.png=404;

D. try_files /images/$uri /images/default.png;

Solution

1. Step 1: Understand file paths in try_files

   To check /images/$uri first, it must be the first argument.

2. Step 2: Choose fallback file

   If the first file is missing, serve /images/default.png as fallback.

3. Step 3: Validate options

   try_files /images/$uri /images/default.png; matches this logic exactly without extra fallbacks or error codes.

4. Final Answer:

   try_files /images/$uri /images/default.png; -> Option D

5. Quick Check:

   try_files lists files in order, fallback last [OK]

Hint: List files in order, fallback last without extra codes [OK]

Common Mistakes:

• Using $uri without /images/ prefix
• Adding unnecessary fallback like =404
• Ending with unrelated fallback like /index.html