Proxy cache key in Nginx - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the proxy cache key using the request URI.

Nginx

proxy_cache_key [1];

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

A$http_user_agent

B$host

C$request_uri

D$remote_addr

Attempts:

3 left

💡 Hint

Common Mistakes

Using $host or $remote_addr as cache key causes cache misses for different URIs.

Using $http_user_agent is unrelated to the request URI.

The proxy_cache_key directive defines the key used to store cached responses. Using $request_uri ensures the cache key is based on the full request URI.

2fill in blank

medium

Complete the code to include the request method in the proxy cache key.

Nginx

proxy_cache_key [1]$request_uri;

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

A$request_method

B$host

C$remote_addr

D$http_cookie

Attempts:

3 left

💡 Hint

Common Mistakes

Using $host or $remote_addr does not reflect the HTTP method.

Using $http_cookie is unrelated to the request method.

Including $request_method in the cache key differentiates cache entries by HTTP method (GET, POST, etc.).

3fill in blank

hard

Fix the error in the proxy cache key to include the host and URI correctly.

Nginx

proxy_cache_key [1]$request_uri;

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

A$http_user_agent

B$request_method

C$remote_addr

D$host

Attempts:

3 left

💡 Hint

Common Mistakes

Using $request_method instead of $host causes incorrect cache keys.

Using $remote_addr or $http_user_agent does not represent the host.

The correct way to include the host and URI is by using $host followed by $request_uri. This ensures the cache key is unique per host and URI.

4fill in blank

hard

Fill both blanks to create a cache key that includes the host and the request method.

Nginx

proxy_cache_key [1][2]$request_uri;

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

A$host

B$request_method

C$remote_addr

D$http_cookie

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of variables can cause unexpected cache behavior.

Using $remote_addr or $http_cookie instead of host or method.

Combining $host and $request_method before $request_uri creates a cache key that varies by host and HTTP method.

5fill in blank

hard

Fill all three blanks to create a cache key that includes the host, request method, and a custom header 'X-User'.

Nginx

proxy_cache_key [1][2][3]$request_uri;

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

A$host

B$request_method

C$http_x_user

D$remote_addr

Attempts:

3 left

💡 Hint

Common Mistakes

Using $remote_addr instead of the custom header.

Forgetting the $http_ prefix for custom headers.

This cache key includes the host, HTTP method, and the custom header X-User (accessed as $http_x_user) before the request URI. This ensures caching varies by these values.

Practice

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

easy

A. To define how nginx identifies and stores cached content

B. To set the maximum size of the cache

C. To specify the cache expiration time

D. To enable SSL for proxy connections

Solution

1. Step 1: Understand the role of proxy_cache_key

   The proxy_cache_key tells nginx how to uniquely identify cached content by combining variables like scheme, host, and URI.

2. Step 2: Differentiate from other cache settings

   Other directives control cache size or expiration, but proxy_cache_key specifically defines the cache lookup key.

3. Final Answer:

   To define how nginx identifies and stores cached content -> Option A

4. Quick Check:

   proxy_cache_key = cache identifier [OK]

Hint: proxy_cache_key sets cache identity, not size or time [OK]

Common Mistakes:

• Confusing cache key with cache size or expiration
• Thinking it enables SSL
• Assuming it controls cache storage location

2. Which of the following is the correct syntax to set a proxy cache key using scheme, host, and request URI in nginx?

easy

A. proxy_cache_key $scheme$host$request_uri;

B. proxy_cache_key $scheme://$host$request_uri;

C. proxy_cache_key $scheme://host$request_uri;

D. proxy_cache_key "$scheme://$host$request_uri";

Solution

1. Step 1: Check syntax for proxy_cache_key

   The value must be a string, so it should be enclosed in double quotes if it contains special characters like ://.

2. Step 2: Verify variable usage

   Variables like $scheme, $host, and $request_uri must be concatenated properly inside quotes.

3. Final Answer:

   proxy_cache_key "$scheme://$host$request_uri"; -> Option D

4. Quick Check:

   Quotes needed for complex keys = proxy_cache_key "$scheme://$host$request_uri"; [OK]

Hint: Use quotes when combining variables with symbols like :// [OK]

Common Mistakes:

• Omitting quotes around the key string
• Missing $ before variables
• Incorrect concatenation without quotes

3. Given this nginx config snippet:

proxy_cache_key "$scheme://$host$request_uri";

What will be the cache key for a request to https://example.com/path/page?query=1?

medium

A. example.com/path/page?query=1

B. https://example.com/path/page?query=1

C. https://example.com/path/page

D. http://example.com/path/page?query=1

Solution

1. Step 1: Substitute variables with request values

   $scheme is 'https', $host is 'example.com', and $request_uri includes path and query: '/path/page?query=1'.

2. Step 2: Combine variables as per the key format

   Joining them gives 'https://example.com/path/page?query=1'.

3. Final Answer:

   https://example.com/path/page?query=1 -> Option B

4. Quick Check:

   Variables combined exactly = https://example.com/path/page?query=1 [OK]

Hint: Remember $request_uri includes query string [OK]

Common Mistakes:

• Ignoring the query string in $request_uri
• Using http instead of https for scheme
• Leaving out the scheme or host

4. You set proxy_cache_key "$scheme://$host$uri"; but nginx caches different query strings as the same content. What is the likely cause?

medium

A. You did not enable proxy_cache_path

B. You used $request_uri which already includes query string

C. You forgot to include $args in the cache key

D. You used double quotes instead of single quotes

Solution

1. Step 1: Understand $uri vs $request_uri

   $uri contains only the path (normalized), excluding the query string. $request_uri includes the query.

2. Step 2: Analyze the symptom

   Different query strings yield the same $uri, hence same cache key, causing shared cache content.

3. Final Answer:

   You forgot to include $args in the cache key -> Option C

4. Quick Check:

   $uri excludes query; add $args [OK]

Hint: $uri lacks query string; add $args [OK]

Common Mistakes:

• Confusing cache key with cache size or expiration
• Thinking it enables SSL
• Assuming it controls cache storage location

5. You want to cache content separately for mobile and desktop users. Which proxy cache key configuration achieves this if user agent contains 'Mobile' for mobile devices?

hard

A. proxy_cache_key "$scheme://$host$request_uri:$is_mobile"; # where $is_mobile is set by map

B. proxy_cache_key "$scheme://$host$request_uri:$http_user_agent ~* Mobile";

C. proxy_cache_key "$scheme://$host$request_uri:$http_user_agent";

D. proxy_cache_key "$scheme://$host$request_uri";

Solution

1. Step 1: Understand the need for conditional cache key

   We want to separate cache for mobile and desktop, so the key must include a variable indicating device type.

2. Step 2: Use a map to set $is_mobile variable

   nginx can use map to set $is_mobile to 'mobile' or 'desktop' based on $http_user_agent matching 'Mobile'. Including $is_mobile in cache key separates caches.

3. Step 3: Evaluate options

   proxy_cache_key "$scheme://$host$request_uri:$http_user_agent"; uses full user agent, which is too specific and causes cache fragmentation. proxy_cache_key "$scheme://$host$request_uri:$http_user_agent ~* Mobile"; is invalid syntax. proxy_cache_key "$scheme://$host$request_uri"; ignores device type. proxy_cache_key "$scheme://$host$request_uri:$is_mobile"; # where $is_mobile is set by map correctly uses $is_mobile set by map.

4. Final Answer:

   proxy_cache_key "$scheme://$host$request_uri:$is_mobile"; # where $is_mobile is set by map -> Option A

5. Quick Check:

   Use map variable for device type in cache key = proxy_cache_key "$scheme://$host$request_uri:$is_mobile"; # where $is_mobile is set by map [OK]

Hint: Use map to create $is_mobile variable for cache key [OK]

Common Mistakes:

• Using full user agent causing too many cache entries
• Trying regex inside proxy_cache_key (invalid)
• Ignoring device type in cache key