Proxy cache key in Nginx - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the effective cache key with this configuration?

Given this nginx proxy cache key configuration, what is the resulting cache key for a request with host 'example.com' and URI '/index.html'?

Nginx

proxy_cache_key "$host$request_uri";

A "example.com/index.html"

B "/index.html"

C "example.com"

D "$host$request_uri"

💡 Hint

The variables $host and $request_uri are replaced by their values in the cache key string.

The proxy_cache_key directive uses variables. Here, $host is 'example.com' and $request_uri is '/index.html', so the key becomes 'example.com/index.html'.

🧠 Conceptual

intermediate

Why customize proxy_cache_key in nginx?

What is the main reason to customize the proxy_cache_key in nginx proxy caching?

A To disable caching completely

B To control how requests are grouped and cached based on request properties

C To set the cache expiration time

D To change the backend server IP address

💡 Hint

Think about what the cache key represents in caching.

The proxy_cache_key defines how nginx identifies unique cache entries. Customizing it lets you control which requests share cached content.

❓ Configuration

advanced

Select the correct proxy_cache_key to cache by host and URI only

Which proxy_cache_key configuration caches responses uniquely by host and URI, ignoring query parameters?

A proxy_cache_key "$host$uri";

B proxy_cache_key "$host$request_uri";

C proxy_cache_key "$host$args";

D proxy_cache_key "$uri$args";

💡 Hint

$uri excludes query parameters, $request_uri includes them.

The $uri variable contains the normalized URI without query parameters, so caching by "$host$uri" ignores query strings.

❓ Troubleshoot

advanced

Why does nginx cache miss occur despite identical URLs?

You configured proxy_cache_key as "$host$request_uri" but see cache misses for requests with same URL but different 'User-Agent' headers. What is the likely cause?

A The proxy_cache_key syntax is invalid causing cache misses

B nginx ignores proxy_cache_key and caches by IP address

C The backend server varies response by 'User-Agent', causing different content despite same cache key

D The cache key does not include 'User-Agent', so cache misses are unexpected

💡 Hint

Consider how backend response variations affect caching.

If backend responses differ by 'User-Agent' but cache key ignores it, nginx caches one version but serves wrong content, so it may bypass cache causing misses.

✅ Best Practice

expert

Best practice for proxy_cache_key with dynamic query parameters

You want to cache responses but ignore certain query parameters like 'session' and 'tracking' in the cache key. Which approach is best?

A Disable caching for requests with query parameters

B Set proxy_cache_key to "$host$request_uri" to include all query parameters

C Use proxy_cache_key "$host$uri$args" without filtering

D Use a map to filter unwanted query parameters and build proxy_cache_key with filtered args

💡 Hint

Think about how to exclude specific query parameters from cache key.

Using a map to filter query parameters lets you exclude unwanted ones from cache key, improving cache hit ratio and avoiding cache fragmentation.