Open file cache in Nginx - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the purpose of the open_file_cache directive in nginx?

nginx uses the open_file_cache directive to improve performance. What does it specifically cache?

A It caches DNS lookups to speed up domain name resolution.

B It caches the entire content of files in memory for faster delivery.

C It caches open file descriptors to reduce file open/close operations.

D It caches HTTP headers to reduce processing time.

💡 Hint

Think about what happens when nginx serves static files repeatedly.

The open_file_cache directive caches file descriptors and metadata to avoid repeated open/close system calls, improving performance when serving files.

❓ Configuration

intermediate

Which configuration snippet correctly enables open_file_cache with 100 max cached files and 60 seconds inactive timeout?

Choose the correct nginx configuration to enable open_file_cache with a maximum of 100 cached files and an inactive timeout of 60 seconds.

A open_file_cache max_files=100 inactive_timeout=60;

B open_file_cache 100 60s;

C open_file_cache max=60 inactive=100s;

D open_file_cache max=100 inactive=60s;

💡 Hint

Check the correct parameter names and syntax for open_file_cache.

The correct syntax uses max= and inactive= with time units, like 60s.

💻 Command Output

advanced

What error will nginx report if open_file_cache is set with an invalid time unit?

Given this configuration snippet:

open_file_cache max=50 inactive=5x;

What error message will nginx show when testing this config?

A nginx: [emerg] invalid time value "5x" in /etc/nginx/nginx.conf:10

B nginx: [warn] unknown directive "open_file_cache" in /etc/nginx/nginx.conf:10

C nginx: [error] failed to start due to syntax error in open_file_cache

D nginx: configuration file /etc/nginx/nginx.conf test is successful

💡 Hint

Look for errors related to invalid time formats in nginx.

nginx reports an emergency error with the invalid time value and line number when a wrong time unit is used.

❓ Troubleshoot

advanced

Why might enabling open_file_cache not improve performance as expected?

You enabled open_file_cache with proper settings, but nginx performance did not improve. Which reason is most likely?

A The <code>open_file_cache_valid</code> directive is set too low, causing frequent cache invalidation.

B The server has too much free memory, so caching is disabled automatically.

C The <code>open_file_cache</code> directive only works for dynamic content, not static files.

D The <code>open_file_cache_min_uses</code> is set to 0, so files are never cached.

💡 Hint

Think about how cache validity affects caching benefits.

If open_file_cache_valid is too low, cached entries expire quickly, causing nginx to reopen files often, reducing caching benefits.

✅ Best Practice

expert

What is the recommended way to configure open_file_cache for a high-traffic static file server?

For a high-traffic nginx server serving mostly static files, which configuration is best practice for open_file_cache?

A open_file_cache max=100 inactive=30s; open_file_cache_valid 5s; open_file_cache_min_uses 1;

B open_file_cache max=10000 inactive=120s; open_file_cache_valid 60s; open_file_cache_min_uses 2;

C open_file_cache max=500 inactive=10s; open_file_cache_valid 1s; open_file_cache_min_uses 0;

D open_file_cache max=50 inactive=300s; open_file_cache_valid 300s; open_file_cache_min_uses 10;

💡 Hint

Consider cache size, validity, and minimum uses for effective caching.

High max cache size and reasonable inactive and valid times with a minimum uses threshold help keep frequently accessed files cached efficiently.