Map directive for variable mapping in Nginx - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a map that sets $cache_bypass to 1 when $arg_nocache is present.

Nginx

map $arg_nocache [1] {
    default 0;
    1 1;
}

Drag options to blanks, or click blank then click option'

A$cache_bypass_value

Bnocache_flag

C$nocache

D$cache_bypass

Attempts:

3 left

💡 Hint

Common Mistakes

Using the source variable instead of the target variable.

Omitting the dollar sign in variable names.

The map directive assigns values to the variable $cache_bypass based on $arg_nocache.

2fill in blank

medium

Complete the map directive to set $backend to 'server1' when $http_host is 'example.com'.

Nginx

map $http_host [1] {
    default backend_default;
    example.com server1;
}

Drag options to blanks, or click blank then click option'

A$server

B$backend

Cbackend

D$host_backend

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name without the dollar sign.

Using an unrelated variable name.

The map directive sets the variable $backend based on the value of $http_host.

3fill in blank

hard

Fix the error in the map directive to correctly map $request_uri to $clean_uri by removing query strings.

Nginx

map $request_uri [1] {
    ~^(?<clean_uri>[^?]+) $clean_uri;
    default $request_uri;
}

Drag options to blanks, or click blank then click option'

A$clean_uri

Bclean_uri

C$uri_clean

D$clean

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the dollar sign.

Using a different variable name than the capture group.

The target variable must be $clean_uri to store the mapped value.

4fill in blank

hard

Fill both blanks to create a map that sets $is_mobile to '1' if $http_user_agent contains 'Mobile', else '0'.

Nginx

map $http_user_agent [1] {
    ~Mobile [2];
    default 0;
}

Drag options to blanks, or click blank then click option'

A$is_mobile

B1

Ctrue

D$mobile_flag

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name without a dollar sign.

Using 'true' instead of '1'.

The map sets $is_mobile to 1 when the user agent contains 'Mobile'.

5fill in blank

hard

Fill all three blanks to create a map that sets $env based on $host: 'prod' for 'example.com', 'dev' for 'dev.example.com', else 'test'.

Nginx

map $host [1] {
    example.com [2];
    dev.example.com [3];
    default test;
}

Drag options to blanks, or click blank then click option'

A$env

Bprod

Cdev

D$environment

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name without a dollar sign.

Mixing up the values for hosts.

The map sets the variable $env to 'prod' or 'dev' based on the host, defaulting to 'test'.

Practice

1. What is the primary purpose of the map directive in nginx configuration?

easy

A. To create new variables based on existing variables

B. To define server blocks for different domains

C. To set up SSL certificates

D. To configure load balancing between servers

Solution

1. Step 1: Understand the role of map in nginx

   The map directive is used to create new variables by mapping values from existing variables.

2. Step 2: Compare with other nginx directives

   Other options like server blocks, SSL, and load balancing serve different purposes unrelated to variable mapping.

3. Final Answer:

   To create new variables based on existing variables -> Option A

4. Quick Check:

   map creates variables [OK]

Hint: Map creates variables from existing ones [OK]

Common Mistakes:

• Confusing map with server block configuration
• Thinking map sets SSL or load balancing
• Assuming map modifies request headers directly

2. Which of the following is the correct syntax to start a map block in nginx?

easy

A. map ($variable, $new_variable) {

B. map $new_variable $variable {

C. map { $variable $new_variable }

D. map $variable $new_variable {

Solution

1. Step 1: Recall the syntax of the map directive

   The correct syntax is map $variable $new_variable { where the first variable is the source and the second is the target.

2. Step 2: Eliminate incorrect syntax

   The incorrect options use wrong order or invalid punctuation for nginx configuration.

3. Final Answer:

   map $variable $new_variable { -> Option D

4. Quick Check:

   map syntax = map $source $target { [OK]

Hint: Map syntax: map $source $target { [OK]

Common Mistakes:

• Swapping source and target variables
• Using parentheses or braces incorrectly
• Missing the $ sign before variables

3. Given this nginx map configuration:

map $http_user_agent $is_mobile {
    default 0;
    ~*Mobile 1;
}

What will be the value of $is_mobile if the user agent is Mozilla/5.0 (Linux; Mobile)?

medium

A. Mobile

B. 0

C. 1

D. default

Solution

1. Step 1: Understand the map pattern matching

   The map uses a case-insensitive regex ~*Mobile to match user agents containing 'Mobile'.

2. Step 2: Check the user agent string

   The user agent contains 'Mobile', so the regex matches and sets $is_mobile to 1.

3. Final Answer:

   1 -> Option C

4. Quick Check:

   Regex match 'Mobile' sets value to 1 [OK]

Hint: Regex ~*Mobile matches user agent containing 'Mobile' [OK]

Common Mistakes:

• Ignoring case-insensitive regex (~*)
• Assuming default value applies despite match
• Confusing variable names

4. Identify the error in this nginx map configuration:

map $request_method $allow_method {
    GET yes;
    POST yes;
    DELETE no
}

medium

A. Missing semicolon after DELETE no

B. Incorrect variable names

C. map directive cannot map request methods

D. Using yes/no instead of 1/0 is invalid

Solution

1. Step 1: Check syntax for each mapping line

   Each line inside map must end with a semicolon. The line DELETE no is missing a semicolon.

2. Step 2: Validate other options

   Variable names are valid, mapping request methods is allowed, and yes/no strings are acceptable values.

3. Final Answer:

   Missing semicolon after DELETE no -> Option A

4. Quick Check:

   Each map line ends with ; [OK]

Hint: Every map entry line ends with a semicolon [OK]

Common Mistakes:

• Omitting semicolons at line ends
• Thinking yes/no are invalid values
• Assuming map can't use request methods

5. You want to create a variable $cache_key that is mobile if the user agent contains 'Mobile', otherwise desktop. Which map configuration correctly achieves this?

hard

A. map $cache_key $http_user_agent {
mobile ~*Mobile;
desktop default;
}

B. map $http_user_agent $cache_key {
~*Mobile mobile;
default desktop;
}

C. map $http_user_agent $cache_key {
default desktop
~*Mobile mobile
}

D. map $http_user_agent $cache_key {
Mobile mobile;
default desktop;
}

Solution

1. Step 1: Confirm correct map syntax and order

   The map directive must have source variable first, target variable second, and each line ends with semicolon.

2. Step 2: Check pattern matching and default

   map $http_user_agent $cache_key { ~*Mobile mobile; default desktop; } uses case-insensitive regex ~*Mobile to match user agents containing 'Mobile' and sets mobile, else desktop.

3. Step 3: Eliminate incorrect options

   map $cache_key $http_user_agent { mobile ~*Mobile; desktop default; } reverses variables, one misses semicolons, another uses exact 'Mobile' without regex and may miss case-insensitive matches.

4. Final Answer:

   map $http_user_agent $cache_key { ~*Mobile mobile; default desktop; } -> Option B

5. Quick Check:

   Correct map syntax with regex and default [OK]

Hint: Use map $source $target with regex and default [OK]

Common Mistakes:

• Swapping source and target variables
• Missing semicolons after lines
• Not using case-insensitive regex for matching