Cache bypass conditions in Nginx - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Cache Bypass with Specific Header

Given the following nginx configuration snippet, what will be the cache behavior when a request contains the header X-Bypass-Cache: true?

Nginx

proxy_cache_bypass $http_x_bypass_cache;
proxy_cache my_cache;
proxy_cache_valid 200 1h;

A The cache will be bypassed and the request will be forwarded to the backend.

B The cache will be used normally, ignoring the header.

C The cache will be cleared for all entries.

D The request will be blocked with a 403 Forbidden error.

💡 Hint

Check how the variable $http_x_bypass_cache controls cache bypass.

The directive proxy_cache_bypass uses the variable $http_x_bypass_cache. If this variable is set (e.g., header present), nginx bypasses the cache and forwards the request to the backend.

❓ Configuration

intermediate

Condition to Bypass Cache for POST Requests

Which nginx configuration snippet correctly bypasses cache for POST requests?

A proxy_cache_bypass $request_method;

B proxy_cache_bypass $request_method = 'POST';

C proxy_cache_bypass $request_method = POST;

D proxy_cache_bypass $request_method =POST;

💡 Hint

The variable $request_method contains the HTTP method. Non-empty values cause bypass.

Setting proxy_cache_bypass $request_method; causes cache bypass for all requests with a method set. Since POST requests have method 'POST', cache is bypassed for POST.

❓ Troubleshoot

advanced

Unexpected Cache Bypass Behavior

An nginx server is configured with:

proxy_cache_bypass $cookie_nocache;

Users report cache is always bypassed even without the cookie nocache. What is the most likely cause?

A The variable <code>$cookie_nocache</code> is empty string, which still triggers bypass.

B The cookie name is case-sensitive and should be <code>noCache</code>.

C The configuration requires <code>proxy_cache_valid</code> to enable caching.

D The variable <code>$cookie_nocache</code> is undefined and treated as empty, so cache is not bypassed.

💡 Hint

Verify the full cache configuration, especially proxy_cache_valid.

The proxy_cache_bypass $cookie_nocache; directive is correct for conditional bypass (bypasses only if cookie present and non-empty). However, caching requires proxy_cache_valid to specify response validity times. Without it, no responses are cached, so all requests go to the backend.

🔀 Workflow

advanced

Implementing Cache Bypass Based on Query Parameter

You want to bypass cache only when the URL contains the query parameter refresh=true. Which workflow correctly implements this in nginx?

A Directly use <code>proxy_cache_bypass $arg_refresh;</code> without any map.

B Use a map to set a variable to 1 if <code>$arg_refresh</code> equals 'true', then use that variable in <code>proxy_cache_bypass</code>.

C Use <code>if ($arg_refresh = 'true') { proxy_cache_bypass 1; }</code> inside location block.

D Set <code>proxy_cache_bypass $query_string;</code> to bypass cache when any query exists.

💡 Hint

Maps are preferred for conditional cache bypass based on variable values.

Using a map allows setting a variable to 1 only when $arg_refresh equals 'true'. Then proxy_cache_bypass uses that variable to bypass cache only in that case.

🧠 Conceptual

expert

Effect of Multiple Conditions in proxy_cache_bypass

Consider this nginx configuration:

proxy_cache_bypass $http_cache_control $cookie_nocache;

What is the effect of listing multiple variables in proxy_cache_bypass?

A Cache is bypassed only if all variables are non-empty (logical AND).

B Cache is bypassed only if the first variable is non-empty; others are ignored.

C Cache is never bypassed because multiple variables cause a syntax error.

D Cache is bypassed if any one of the variables is non-empty (logical OR).

💡 Hint

Check how nginx evaluates multiple variables in proxy_cache_bypass.

When multiple variables are listed, nginx bypasses cache if any variable is non-empty. This acts like a logical OR condition.