Cache validity rules in Nginx - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Cache validity with expires directive

What is the HTTP response header Expires value when the following nginx configuration is applied?

location /images/ {
  expires 10d;
}

A Expires header is set to 10 minutes from the response time

B Expires header is set to 10 seconds from the response time

C Expires header is not set by this configuration

D Expires header is set to 10 days from the response time

💡 Hint

The expires directive sets the cache duration relative to the response time.

The expires 10d; directive tells nginx to add an Expires header 10 days in the future from the response time, making the cache valid for 10 days.

🧠 Conceptual

intermediate

Understanding cache-control max-age

Which statement correctly describes the effect of add_header Cache-Control "max-age=3600"; in nginx configuration?

A It sets the cache to expire 3600 seconds after the response is received

B It disables caching for the resource

C It sets the cache to expire immediately

D It sets the cache to expire after 3600 minutes

💡 Hint

max-age is measured in seconds.

The Cache-Control: max-age=3600 header tells browsers and proxies to consider the cached response fresh for 3600 seconds (1 hour) after it is received.

❓ Troubleshoot

advanced

Diagnosing cache not expiring as expected

You configured nginx with expires 5m; but clients still receive cached content after 10 minutes. What is the most likely cause?

A The upstream server is sending conflicting Cache-Control headers that override nginx

B The <code>expires</code> directive only works for static files, not dynamic content

C The <code>expires</code> directive requires a reload of nginx to take effect

D The client browser ignores all cache headers by default

💡 Hint

Check headers sent by the backend server.

If the backend server sends Cache-Control headers with longer max-age or no-cache, they can override nginx's expires directive, causing clients to cache longer than expected.

🔀 Workflow

advanced

Configuring cache validity for API responses

You want to cache API responses for 30 seconds but ensure clients always revalidate after that. Which nginx configuration snippet achieves this?

A expires 30s; add_header Cache-Control "no-cache";

B expires 30s; add_header Cache-Control "public";

C add_header Cache-Control "max-age=30, must-revalidate";

D add_header Cache-Control "no-store";

💡 Hint

Use Cache-Control directives to control revalidation.

The max-age=30, must-revalidate tells clients to cache for 30 seconds but revalidate with the server after that period before using the cached response.

✅ Best Practice

expert

Best practice for cache validity with varying content

You serve images that rarely change and JSON data that updates frequently. What is the best cache validity strategy in nginx to optimize performance and freshness?

A Set the same expires time (e.g., 1d) for both images and JSON for simplicity

B Set long expires (e.g., 30d) for images and short max-age (e.g., 10s) with must-revalidate for JSON

C Disable caching for images and set long max-age for JSON

D Use no-store for both images and JSON to avoid caching issues

💡 Hint

Different content types need different cache durations.

Images that rarely change benefit from long cache validity to reduce load, while JSON data should have short cache times with revalidation to ensure freshness.