JSON error responses in Nginx - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this nginx error response configuration?

Given this nginx configuration snippet for JSON error response, what will be the exact JSON output when a 404 error occurs?

Nginx

error_page 404 = /custom_404.json;
location = /custom_404.json {
  default_type application/json;
  return 404 '{"error": "Not Found", "code": 404}';
}

A <html><body>404 Not Found</body></html>

B SyntaxError: invalid JSON

C {"error": "Page Missing", "code": 404}

D {"error": "Not Found", "code": 404}

💡 Hint

Look at the return directive and the content type set.

The configuration sets the content type to application/json and returns a JSON string with error and code fields for 404 errors.

❓ Configuration

intermediate

Which configuration snippet correctly returns a JSON error for 500 errors?

Select the nginx configuration snippet that correctly returns a JSON error response with status 500 and message "Internal Server Error".

A

error_page 500 = /500.json;
location = /500.json {
  default_type text/html;
  return 500 '{"error": "Internal Server Error", "code": 500}';
}

B

error_page 500 /500.json;
location /500.json {
  add_header Content-Type application/json;
  return 500 '{"error": "Internal Server Error", "code": 500}';
}

C

error_page 500 = /500.json;
location = /500.json {
  default_type application/json;
  return 500 '{"error": "Internal Server Error", "code": 500}';
}

D

error_page 500 = /500.json;
location = /500.json {
  default_type application/json;
  return 404 '{"error": "Internal Server Error", "code": 500}';
}

💡 Hint

Check the status code in the return directive and the content type.

Option C correctly sets the error_page, location with exact match, content type application/json, and returns status 500 with the correct JSON message.

❓ Troubleshoot

advanced

Why does this nginx JSON error response return HTML instead of JSON?

You configured nginx as below to return JSON on 403 errors, but the client receives HTML instead. What is the most likely cause?

Nginx

error_page 403 = /403.json;
location = /403.json {
  return 403 '{"error": "Forbidden", "code": 403}';
}

A Missing default_type application/json directive in the location block

B The return directive must use double quotes instead of single quotes

C The error_page directive should not use '=' sign

D The location block must be named /error/403.json instead of /403.json

💡 Hint

Check what content type nginx sends by default if not specified.

Without default_type application/json, nginx defaults to text/html, so the client receives HTML instead of JSON.

✅ Best Practice

advanced

What is the best practice to serve consistent JSON error responses in nginx?

Which approach ensures all error responses (e.g., 400, 403, 404, 500) return JSON with proper status and message?

A Use a single error_page directive for all errors pointing to one JSON file and set default_type application/json globally

B Define separate error_page and location blocks for each error code with JSON return and default_type application/json

C Use error_page directives without '=' and return HTML pages with embedded JSON scripts

D Configure error_page to redirect to an external API that returns JSON error messages

💡 Hint

Think about how to customize each error code's message and status properly.

Separate error_page and location blocks allow precise control of status codes and JSON messages per error, ensuring consistency.

🧠 Conceptual

expert

What happens if you omit the '=' sign in error_page directive for JSON error responses?

Consider this directive: error_page 404 /404.json; without '=' sign. What is the effect on the HTTP status code and response body?

A Nginx issues an internal redirect to /404.json but keeps the original 404 status code

B Nginx issues an external redirect changing the status code to 302

C Nginx changes the status code to 200 and serves /404.json content

D Nginx returns a syntax error and fails to start

💡 Hint

Understand the difference between internal redirect with and without '=' in error_page.

Without '=', nginx internally redirects to the URI but preserves the original error status code, so client sees 404 with content from /404.json.

Practice

1. What is the main benefit of sending JSON error responses in nginx?

easy

A. They automatically fix server errors without manual intervention.

B. They make error information easy for applications to read and process.

C. They reduce the size of error messages to save bandwidth.

D. They prevent users from seeing any error messages.

Solution

1. Step 1: Understand JSON error response purpose

   JSON error responses format error details in a way apps can easily parse and handle.

2. Step 2: Compare options

   Only They make error information easy for applications to read and process. correctly states the benefit of JSON error responses; others are incorrect or unrelated.

3. Final Answer:

   They make error information easy for applications to read and process. -> Option B

4. Quick Check:

   JSON error responses = easy app reading [OK]

Hint: JSON errors help apps read errors clearly [OK]

Common Mistakes:

• Thinking JSON errors fix server issues automatically
• Believing JSON errors hide all error messages
• Assuming JSON errors reduce bandwidth significantly

2. Which nginx directive is used to specify a custom error page that returns JSON?

easy

A. error_page

B. listen

C. proxy_pass

D. server_name

Solution

1. Step 1: Identify directive for custom error pages

   The error_page directive tells nginx which page to serve on specific errors.

2. Step 2: Eliminate unrelated directives

   proxy_pass forwards requests, listen sets ports, server_name sets domain names; none define error pages.

3. Final Answer:

   error_page -> Option A

4. Quick Check:

   Custom error page directive = error_page [OK]

Hint: Use error_page to set custom error responses [OK]

Common Mistakes:

• Confusing proxy_pass with error_page
• Using listen or server_name for error handling
• Forgetting to set content type for JSON

3. Given this nginx config snippet, what is the JSON response body for a 404 error?

error_page 404 /404.json;
location = /404.json {
  internal;
  default_type application/json;
  return 404 '{"error":"Not Found"}';
}

medium

A. 404 Not Found

B. Not Found

C. {"error":"Not Found"}

D. Error 404

Solution

1. Step 1: Analyze the error_page and location block

   The 404 error triggers /404.json, which is internal and returns JSON with content type application/json.

2. Step 2: Check the return statement

   The return sends status 404 with JSON string '{"error":"Not Found"}' as the body.

3. Final Answer:

   {"error":"Not Found"} -> Option C

4. Quick Check:

   Return JSON string = {"error":"Not Found"} [OK]

Hint: Look at return content for JSON body [OK]

Common Mistakes:

• Assuming default HTML error page is returned
• Ignoring internal directive effect
• Confusing status code text with response body

4. You configured nginx to return JSON errors but clients receive HTML error pages instead. What is the likely mistake?

medium

A. The server_name directive is not set.

B. The error_page directive is missing or incorrect.

C. The return directive uses invalid JSON syntax.

D. The internal directive is missing in the error location block.

Solution

1. Step 1: Understand internal directive role

   The internal directive prevents direct client access to error pages, ensuring nginx uses them only for error responses.

2. Step 2: Identify why HTML is returned

   If internal is missing, clients can access the error page URL directly, causing nginx to serve default HTML instead of JSON error.

3. Final Answer:

   The internal directive is missing in the error location block. -> Option D

4. Quick Check:

   Missing internal = HTML errors shown [OK]

Hint: Always mark error locations internal for JSON errors [OK]

Common Mistakes:

• Forgetting internal causes direct access to error pages
• Blaming server_name for error response format
• Assuming JSON syntax error causes HTML output

5. How would you configure nginx to return a JSON error response with status 500 and body {"error":"Server Error"} using an internal location?

hard

A. error_page 500 /500.json;
location = /500.json {
internal;
default_type application/json;
return 500 '{"error":"Server Error"}';
}

B. error_page 500 /500.html;
location = /500.html {
internal;
default_type text/html;
return 500 'Server Error';
}

C. location /500.json {
return 500 '{"error":"Server Error"}';
}

D. error_page 500 /500.json;
location /500.json {
default_type application/json;
return 500 '{"error":"Server Error"}';
}

Solution

1. Step 1: Use error_page to map 500 to JSON location

   The directive error_page 500 /500.json; tells nginx to use /500.json for 500 errors.

2. Step 2: Define internal location with JSON content type and return JSON body

   The location must be internal to prevent direct access, set default_type application/json;, and return the JSON string with status 500.

3. Step 3: Verify options

   error_page 500 /500.json; location = /500.json { internal; default_type application/json; return 500 '{"error":"Server Error"}'; } matches all requirements. error_page 500 /500.html; location = /500.html { internal; default_type text/html; return 500 '

   Server Error

   '; } uses HTML. The others lack the internal directive or miss the error_page directive.

4. Final Answer:

   error_page 500 /500.json; location = /500.json { internal; default_type application/json; return 500 '{"error":"Server Error"}'; } -> Option A

5. Quick Check:

   Use error_page + internal + JSON return [OK]

Hint: Map error_page, mark internal, set JSON content, return JSON [OK]

Common Mistakes:

• Omitting internal directive
• Using wrong content type
• Not escaping JSON properly
• Not mapping error_page to location