FastCGI cache in Nginx - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

FastCGI cache status header output

You have enabled FastCGI cache in nginx with the directive fastcgi_cache_use_stale error timeout updating. When a cached response is served, nginx adds a header X-Cache-Status. What is the value of this header when nginx serves a stale cached response due to an upstream timeout?

A "HIT"

B "MISS"

C "STALE"

D "BYPASS"

💡 Hint

Think about what happens when nginx serves a cached response that is not fresh but still usable due to an upstream error.

The X-Cache-Status header shows STALE when nginx serves a stale cached response because the upstream server timed out or returned an error, and the fastcgi_cache_use_stale directive allows serving stale content in such cases.

❓ Configuration

intermediate

Correct FastCGI cache key configuration

Which of the following fastcgi_cache_key directives correctly creates a cache key that includes the host, request URI, and query string to uniquely cache requests?

A fastcgi_cache_key "$host$uri$is_args$args";

B fastcgi_cache_key "$host$uri$query_string";

C fastcgi_cache_key "$host$uri$args";

D fastcgi_cache_key "$host$request_uri$query_string";

💡 Hint

Remember that $is_args adds a '?' only if there are query arguments.

The correct cache key uses $host$uri$is_args$args. The $uri does not include the query string, so $is_args$args is used to append query parameters only if they exist, ensuring proper formatting without duplication.

❓ Troubleshoot

advanced

Diagnosing why FastCGI cache is not storing responses

You configured FastCGI cache in nginx, but no cached files appear in the cache directory after requests. Which of the following is the most likely cause?

A The <code>fastcgi_cache_lock</code> directive is enabled.

B The <code>fastcgi_cache_valid</code> directive is set to 0 seconds.

C The <code>fastcgi_cache_use_stale</code> directive is not set.

D The <code>fastcgi_cache_path</code> directive is missing or incorrectly set.

💡 Hint

Check if the cache directory and zone are properly defined.

If fastcgi_cache_path is missing or incorrect, nginx does not know where to store cached files, so no cache files are created.

🔀 Workflow

advanced

Order of directives to enable FastCGI cache

Arrange the following nginx configuration steps in the correct order to enable FastCGI caching for PHP requests.

A 1,2,4,3

B 1,3,2,4

C 2,1,3,4

D 1,2,3,4

💡 Hint

Think about defining the cache storage first, then key, then validity, and finally enabling cache usage.

First, fastcgi_cache_path defines where cache is stored. Then fastcgi_cache_key defines how to identify cached items. Next, fastcgi_cache_valid sets how long to keep cached items. Finally, fastcgi_cache is enabled in the location block to activate caching.

✅ Best Practice

expert

Best practice for cache purging with FastCGI cache

Which method is considered best practice to safely purge specific cached content in nginx FastCGI cache without restarting nginx or deleting cache files manually?

A Set <code>fastcgi_cache_valid</code> to a very low value to expire cache quickly.

B Use <code>fastcgi_cache_purge</code> directive with a location block and send HTTP PURGE requests.

C Manually delete cache files from the cache directory and reload nginx.

D Restart nginx to clear all cached content.

💡 Hint

Look for a method that allows selective cache removal via HTTP requests.

The fastcgi_cache_purge directive allows defining a location that accepts HTTP PURGE requests to selectively remove cached items safely without downtime or manual file operations.