Proxy cache basics in Nginx - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to enable proxy caching in nginx.

Nginx

proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=my_cache:10m [1] inactive=60m;

Drag options to blanks, or click blank then click option'

Amax_cache_size=1g

Bmax_size=1g

Cmax_cache=500m

Dmax_size=100m

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'max_cache' instead of 'max_size' causes nginx to ignore the limit.

Setting size without units (like '100') causes errors.

The max_size directive sets the maximum size of the cache. Here, max_size=100m limits the cache to 100 megabytes.

2fill in blank

medium

Complete the code to set the proxy cache key to the request URI.

Nginx

proxy_cache_key [1];

Drag options to blanks, or click blank then click option'

A$request_method

B$host

C$request_uri

D$remote_addr

Attempts:

3 left

💡 Hint

Common Mistakes

Using $request_method caches by HTTP method, which is not unique enough.

Using $remote_addr caches by client IP, which is unrelated to the resource.

The proxy_cache_key defines the cache key. Using $request_uri caches based on the full request URI.

3fill in blank

hard

Fix the error in the proxy cache configuration to enable caching for 10 minutes.

Nginx

proxy_cache_valid 200 302 [1];

Drag options to blanks, or click blank then click option'

A10min

B10m

C600s

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using '10' without units causes nginx to ignore the setting.

Using '10min' is not recognized by nginx.

The proxy_cache_valid directive requires a time with units like 'm' for minutes. '10m' means 10 minutes.

4fill in blank

hard

Fill both blanks to set cache control headers and enable proxy caching in the location block.

Nginx

location / {
    proxy_cache [1];
    add_header [2] 'HIT from cache';
}

Drag options to blanks, or click blank then click option'

Amy_cache

BX-Cache-Status

CCache-Control

Dcache_zone

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Cache-Control' as header name here is incorrect for cache hit indication.

Using 'cache_zone' instead of the actual cache zone name causes errors.

proxy_cache my_cache; enables caching using the defined cache zone. add_header X-Cache-Status 'HIT from cache'; adds a header to indicate cache hits.

5fill in blank

hard

Fill all three blanks to create a dictionary of cached responses with keys as request URIs and values as status codes greater than 200.

Nginx

cached_responses = { [1]: [2] for [3] in responses if responses[[1]] > 200 }

Drag options to blanks, or click blank then click option'

Auri

Bresponses[uri]

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for key and loop variable causes errors.

Using 'status' as loop variable without defining it causes NameError.

This dictionary comprehension uses uri as the key and responses[uri] as the value, filtering for status codes greater than 200.

Practice

1. What is the main purpose of proxy_cache in nginx?

easy

A. To store copies of web responses for faster delivery

B. To block unwanted web requests

C. To encrypt web traffic

D. To balance load between servers

Solution

1. Step 1: Understand proxy_cache role

   The proxy_cache directive tells nginx to save copies of responses from the backend server.

2. Step 2: Identify purpose of caching

   Storing these copies helps nginx deliver content faster to users without asking the backend every time.

3. Final Answer:

   To store copies of web responses for faster delivery -> Option A

4. Quick Check:

   proxy_cache = store copies for speed [OK]

Hint: proxy_cache saves responses to speed up delivery [OK]

Common Mistakes:

• Confusing proxy_cache with load balancing
• Thinking proxy_cache encrypts traffic
• Assuming proxy_cache blocks requests

2. Which of the following is the correct syntax to define a cache path in nginx?

easy

A. proxy_cache_path /data/nginx/cache keys_zone=mycache:10m levels=1:2

B. proxy_cache_path /data/nginx/cache levels=1:2 keys_zone=mycache:10m;

C. proxy_cache_path keys_zone=mycache:10m /data/nginx/cache levels=1:2;

D. proxy_cache_path levels=1:2 keys_zone=mycache:10m /data/nginx/cache;

Solution

1. Step 1: Recall correct order of proxy_cache_path

   The correct syntax starts with the cache directory path, then options like levels and keys_zone.

2. Step 2: Match syntax with options order

   proxy_cache_path /data/nginx/cache levels=1:2 keys_zone=mycache:10m; correctly places the path first, followed by levels and keys_zone with proper separators and semicolon.

3. Final Answer:

   proxy_cache_path /data/nginx/cache levels=1:2 keys_zone=mycache:10m; -> Option B

4. Quick Check:

   Path first, then options = proxy_cache_path /data/nginx/cache levels=1:2 keys_zone=mycache:10m; [OK]

Hint: Cache path starts with directory, then options [OK]

Common Mistakes:

• Placing keys_zone before path
• Missing semicolon at end
• Wrong order of parameters

3. Given this nginx config snippet:

proxy_cache_path /tmp/cache keys_zone=mycache:10m;
server {
  location / {
    proxy_cache mycache;
    proxy_cache_valid 200 10m;
    proxy_pass http://backend;
  }
}

What happens when a client requests a page for the first time?

medium

A. nginx fetches from backend and caches the response

B. nginx serves the cached page immediately

C. nginx returns an error because cache is empty

D. nginx ignores cache and always fetches from backend

Solution

1. Step 1: Understand first request behavior

   On the first request, cache is empty, so nginx must get the response from the backend server.

2. Step 2: Recognize caching after fetch

   After fetching, nginx stores the response in cache for future requests within 10 minutes.

3. Final Answer:

   nginx fetches from backend and caches the response -> Option A

4. Quick Check:

   First request = fetch then cache [OK]

Hint: First request fetches backend, then caches response [OK]

Common Mistakes:

• Assuming cache serves before first fetch
• Thinking nginx errors if cache empty
• Believing cache is ignored always

4. You set proxy_cache_valid 200 5m; but cached responses are never used. What is a likely cause?

medium

A. The keys_zone size is too small

B. The cache path directory does not exist

C. The backend server returns status 404 instead of 200

D. The proxy_cache directive is missing in the location block

Solution

1. Step 1: Check proxy_cache usage

   Without proxy_cache enabled in the location, caching won't happen even if proxy_cache_valid is set.

2. Step 2: Understand effect of missing proxy_cache

   Missing this directive means nginx never stores or serves cached responses, causing cache to be unused.

3. Final Answer:

   The proxy_cache directive is missing in the location block -> Option D

4. Quick Check:

   Missing proxy_cache disables caching [OK]

Hint: proxy_cache must be set to enable caching [OK]

Common Mistakes:

• Assuming cache path missing causes no cache use
• Thinking backend status unrelated
• Believing keys_zone size stops caching

5. You want nginx to cache responses with status 200 for 10 minutes and status 404 for 1 minute. Which config snippet achieves this?

hard

A. proxy_cache_valid 200 10m, 404 1m;

B. proxy_cache_valid 10m 200; proxy_cache_valid 1m 404;

C. proxy_cache_valid 200 10m; proxy_cache_valid 404 1m;

D. ;m1 404 ,m01 002 dilav_ehcac_yxorp

Solution

1. Step 1: Recall proxy_cache_valid syntax

   The correct syntax is proxy_cache_valid [status] [time]; for each status separately.

2. Step 2: Identify correct multiple directives

   Using two separate proxy_cache_valid lines for 200 and 404 with their times is valid and clear.

3. Final Answer:

   proxy_cache_valid 200 10m; proxy_cache_valid 404 1m; -> Option C

4. Quick Check:

   Separate lines for each status = proxy_cache_valid 200 10m; proxy_cache_valid 404 1m; [OK]

Hint: Use separate proxy_cache_valid lines per status [OK]

Common Mistakes:

• Combining statuses in one line incorrectly
• Using commas instead of semicolons
• Reversing time and status order