Map directive for variable mapping in Nginx - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of Nginx map directive with simple variable mapping

Given the following Nginx configuration snippet, what will be the value of the variable $color when the request URI is /blue?

Nginx

map $uri $color {
    default red;
    /blue blue;
    /green green;
}

A empty string

B red

C green

D blue

💡 Hint

The map directive assigns values based on matching keys; if no match, it uses default.

The map directive checks the $uri. Since the URI is /blue, it matches the key /blue and assigns blue to $color.

🧠 Conceptual

intermediate

Purpose of the Nginx map directive

What is the primary purpose of the Nginx map directive?

A To set up SSL certificates for HTTPS

B To rewrite URLs before processing requests

C To create a new variable by mapping one variable's value to another based on conditions

D To define server blocks for different domains

💡 Hint

Think about how you can assign values dynamically based on another variable's value.

The map directive creates a new variable whose value depends on the value of another variable, allowing conditional logic in configuration.

❓ Configuration

advanced

Correct Nginx map syntax for IP-based access control

Which of the following Nginx map configurations correctly sets $allowed to 1 for IP 192.168.1.100 and 0 for all others?

A

map $remote_addr $allowed {
    192.168.1.100 1;
    default 0;
}

B

map $remote_addr $allowed {
    default 0;
    192.168.1.100 1;
}

C

map $remote_addr $allowed {
    192.168.1.100:1;
    default:0;
}

D

map $remote_addr $allowed {
    192.168.1.100 => 1;
    default => 0;
}

💡 Hint

Check the syntax for key-value pairs inside the map block.

Option A uses the correct syntax: key and value separated by space and ending with semicolon. Other options have syntax errors.

❓ Troubleshoot

advanced

Troubleshooting unexpected variable value in Nginx map

You have this map directive:

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

But $is_mobile is always 0 even when accessing from a mobile browser. What is the most likely cause?

A The variable <code>$http_user_agent</code> is empty or not passed correctly

B The map directive does not support regular expressions

C The <code>~*</code> regex pattern is case-sensitive and should be <code>~</code>

D The map directive must be placed inside the server block, not http block

💡 Hint

Consider if the variable used in the map has the expected value during request processing.

If $http_user_agent is empty or missing, the regex match will never succeed, so $is_mobile stays at default 0.

🔀 Workflow

expert

Order of evaluation in Nginx map directive with overlapping keys

Consider this map directive:

map $uri $page_type {
    /about about_page;
    ~^/about/us about_us_page;
    default other_page;
}

What will be the value of $page_type for the request URI /about/us?

A about_page

B about_us_page

C other_page

D empty string

💡 Hint

The map directive evaluates keys in the order they appear; the first matching key wins.

The map directive checks keys in the order they appear. The URI '/about/us' does not exactly match '/about', but matches the regex '~^/about/us', so $page_type is set to 'about_us_page'.