Proxy cache basics in Nginx - Mini Project: Build & Apply

Proxy cache basics

📖 Scenario: You are setting up a simple web server proxy using nginx. To improve performance, you want to add caching so that repeated requests for the same content are served faster.

🎯 Goal: Build a basic nginx proxy cache configuration that caches responses from a backend server and serves cached content for repeated requests.

📋 What You'll Learn

Create a cache path configuration with a specific name and location

Define a proxy cache zone with a given name

Configure a server block to use the proxy cache for requests

Print the final nginx configuration to verify the setup

💡 Why This Matters

🌍 Real World

Proxy caching is used in web servers to speed up response times by storing copies of backend responses. This reduces load on backend servers and improves user experience.

💼 Career

Understanding proxy cache basics is important for DevOps engineers and system administrators who manage web infrastructure and optimize performance.

1

Create cache path configuration

Create a cache path configuration using proxy_cache_path with the path /var/cache/nginx, a cache zone named my_cache with 10 megabytes of storage, and set inactive=60m.

Nginx

# Your code here

Hint

Use proxy_cache_path directive with the exact path, zone name, size, and inactive time.

2

Add proxy cache to server block

Add a server block with listen 80; and location / that proxies requests to http://backend_server. Inside the location block, add the directive proxy_cache my_cache; to enable caching using the cache zone my_cache.

Nginx

proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=my_cache:10m inactive=60m;
# Your code here

Hint

Define a server block with listen 80; and a location / block that includes proxy_pass and proxy_cache directives.

3

Add proxy cache key and valid time

Inside the location / block, add the directive proxy_cache_key "$scheme$request_method$host$request_uri"; to define the cache key. Also add proxy_cache_valid 200 302 10m; to cache successful responses for 10 minutes.

Nginx

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

server {
    listen 80;

    location / {
        proxy_pass http://backend_server;
        proxy_cache my_cache;
        # Your code here
    }
}

Hint

Use proxy_cache_key with the exact string and proxy_cache_valid for status codes 200 and 302 with 10 minutes duration.

4

Print the final nginx configuration

Print the entire nginx configuration by writing print(config) where config is a string variable containing the full configuration from previous steps.

Nginx

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

server {
    listen 80;

    location / {
        proxy_pass http://backend_server;
        proxy_cache my_cache;
        proxy_cache_key "$scheme$request_method$host$request_uri";
        proxy_cache_valid 200 302 10m;
    }
}'''

# Print the config below
# Your code here

Hint

Use print(config) to display the full nginx configuration string.

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