FastCGI cache in Nginx - Mini Project: Build & Apply

Setting Up FastCGI Cache in Nginx

📖 Scenario: You manage a busy website using Nginx as the web server. To improve performance and reduce load on your backend PHP server, you want to set up FastCGI caching. This cache will store dynamic page responses temporarily, so repeated requests are served faster.

🎯 Goal: Learn how to configure FastCGI cache in Nginx step-by-step. You will create the cache path, define cache settings, apply caching to a server block, and verify the cache is working.

📋 What You'll Learn

Create a FastCGI cache path with specific keys and inactive time

Define cache key and cache zone in Nginx configuration

Apply FastCGI cache settings to a server location block

Test and display cache status using HTTP headers

💡 Why This Matters

🌍 Real World

FastCGI caching speeds up dynamic websites by storing generated pages temporarily, reducing backend load and improving user experience.

💼 Career

Understanding FastCGI cache setup is essential for DevOps roles managing high-traffic web servers and optimizing performance.

1

Create FastCGI Cache Path

Create a FastCGI cache path called fastcgi_cache_path with the directory /var/cache/nginx/fastcgi_cache, a cache key zone named FASTCGI_CACHE with 10 megabytes of storage, and set the inactive time to 60m.

Nginx

# Your code here

Hint

Use fastcgi_cache_path directive with levels, keys_zone, and inactive parameters.

2

Define Cache Key and Zone

Define a variable $cache_key that combines $scheme, $host, and $request_uri. Then, inside the http block, set fastcgi_cache_key to $cache_key and reference the cache zone FASTCGI_CACHE.

Nginx

fastcgi_cache_path /var/cache/nginx/fastcgi_cache levels=1:2 keys_zone=FASTCGI_CACHE:10m inactive=60m;
# Your code here

Hint

Use set to define $cache_key. Inside http block, set fastcgi_cache_key and fastcgi_cache.

3

Apply FastCGI Cache to Server Location

Inside the server block, add a location / block. Configure it to use fastcgi_cache FASTCGI_CACHE, enable fastcgi_cache_valid 200 10m to cache successful responses for 10 minutes, and set fastcgi_pass to unix:/run/php/php7.4-fpm.sock.

Nginx

fastcgi_cache_path /var/cache/nginx/fastcgi_cache levels=1:2 keys_zone=FASTCGI_CACHE:10m inactive=60m;

set $cache_key "$scheme://$host$request_uri";

http {
    fastcgi_cache_key $cache_key;
    fastcgi_cache FASTCGI_CACHE;

    server {
        listen 80;
        server_name example.com;

        location / {
            # Your code here
        }
    }
}

Hint

Inside location /, set fastcgi_cache, fastcgi_cache_valid, and fastcgi_pass directives.

4

Verify FastCGI Cache Status

Add a header X-Cache-Status inside the location / block to show cache status using add_header X-Cache-Status $upstream_cache_status;. Then, print the command to test the cache status by running curl -I http://example.com/.

Nginx

fastcgi_cache_path /var/cache/nginx/fastcgi_cache levels=1:2 keys_zone=FASTCGI_CACHE:10m inactive=60m;

set $cache_key "$scheme://$host$request_uri";

http {
    fastcgi_cache_key $cache_key;
    fastcgi_cache FASTCGI_CACHE;

    server {
        listen 80;
        server_name example.com;

        location / {
            fastcgi_cache FASTCGI_CACHE;
            fastcgi_cache_valid 200 10m;
            fastcgi_pass unix:/run/php/php7.4-fpm.sock;
            # Your code here
        }
    }
}

# Print the curl command below

Hint

Use add_header X-Cache-Status $upstream_cache_status; inside location /. Then print the curl command to test.

Practice

1. What is the main purpose of enabling FastCGI cache in nginx?

easy

A. To store dynamic page responses and serve them faster next time

B. To block all dynamic content from being served

C. To increase the size of the nginx log files

D. To disable backend server processing completely

Solution

1. Step 1: Understand FastCGI cache function

   FastCGI cache stores dynamic content generated by backend servers temporarily.

2. Step 2: Identify the benefit

   Serving cached content reduces backend load and speeds up response time.

3. Final Answer:

   To store dynamic page responses and serve them faster next time -> Option A

4. Quick Check:

   FastCGI cache purpose = store and speed up [OK]

Hint: FastCGI cache speeds up dynamic pages by storing them [OK]

Common Mistakes:

• Thinking it blocks dynamic content
• Confusing cache with logging
• Assuming it disables backend servers

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

easy

A. fastcgi_cache /path/to/cache keys_zone=mycache inactive=60m;

B. fastcgi_cache_zone /path/to/cache keys_zone=mycache:10m inactive=60m;

C. fastcgi_cache_path keys_zone=mycache:10m /path/to/cache inactive=60m;

D. fastcgi_cache_path /path/to/cache levels=1:2 keys_zone=mycache:10m inactive=60m;

Solution

1. Step 1: Recall fastcgi_cache_path syntax

   The correct syntax includes path, levels, keys_zone with size, and inactive time.

2. Step 2: Match options with syntax

   fastcgi_cache_path /path/to/cache levels=1:2 keys_zone=mycache:10m inactive=60m; matches the correct order and parameters exactly.

3. Final Answer:

   fastcgi_cache_path /path/to/cache levels=1:2 keys_zone=mycache:10m inactive=60m; -> Option D

4. Quick Check:

   Correct fastcgi_cache_path syntax = fastcgi_cache_path /path/to/cache levels=1:2 keys_zone=mycache:10m inactive=60m; [OK]

Hint: Remember: fastcgi_cache_path needs path, levels, keys_zone [OK]

Common Mistakes:

• Mixing keys_zone and path order
• Omitting levels parameter
• Using fastcgi_cache instead of fastcgi_cache_path

3. Given this nginx config snippet:

fastcgi_cache_path /var/cache/nginx levels=1:2 keys_zone=cache_zone:10m inactive=30m;
server {
  location ~ \.php$ {
    fastcgi_cache cache_zone;
    fastcgi_cache_valid 200 10m;
    fastcgi_pass backend;
  }
}

What happens when a PHP page is requested twice within 10 minutes?

medium

A. The cache is cleared after the first request

B. Both requests are forwarded to the backend server

C. The second request is served from cache, speeding up response

D. The second request returns a 404 error

Solution

1. Step 1: Understand fastcgi_cache_valid 200 10m

   This means HTTP 200 responses are cached for 10 minutes.

2. Step 2: Analyze repeated request behavior

   The first request caches the response; the second request within 10 minutes uses cache.

3. Final Answer:

   The second request is served from cache, speeding up response -> Option C

4. Quick Check:

   Cache valid time means reuse cached response [OK]

Hint: fastcgi_cache_valid sets cache duration for status codes [OK]

Common Mistakes:

• Assuming backend always handles requests
• Thinking cache clears after first request
• Confusing cache duration with cache clearing

4. You configured FastCGI cache but notice no caching happens. Which nginx directive is most likely missing?

medium

A. fastcgi_cache_path

B. fastcgi_cache_key

C. fastcgi_cache_valid

D. fastcgi_pass

Solution

1. Step 1: Identify required directives for caching

   fastcgi_cache_path defines cache storage; fastcgi_cache_valid sets cache time; fastcgi_pass sends requests to backend.

2. Step 2: Understand fastcgi_cache_key role

   fastcgi_cache_key defines how requests are identified for caching; missing it disables caching.

3. Final Answer:

   fastcgi_cache_key -> Option B

4. Quick Check:

   Missing cache key disables caching [OK]

Hint: Without fastcgi_cache_key, nginx can't store cache properly [OK]

Common Mistakes:

• Forgetting to set fastcgi_cache_key
• Confusing fastcgi_cache_valid with cache enabling
• Assuming fastcgi_pass controls caching

5. You want to cache PHP responses but exclude logged-in users identified by a cookie user_session. Which configuration snippet correctly disables cache for logged-in users?

hard

A. fastcgi_no_cache $cookie_user_session;

B. fastcgi_cache_valid 200 10m if_not $cookie_user_session;

C. fastcgi_cache_key $cookie_user_session;

D. fastcgi_cache_bypass $cookie_user_session;

Solution

1. Step 1: Understand directives controlling cache bypass

   fastcgi_no_cache disables caching when its variable is true; fastcgi_cache_bypass skips cache lookup but may still cache response.

2. Step 2: Identify correct directive for excluding logged-in users

   fastcgi_no_cache $cookie_user_session; disables caching for requests with that cookie, preventing cached content for logged-in users.

3. Final Answer:

   fastcgi_no_cache $cookie_user_session; -> Option A

4. Quick Check:

   fastcgi_no_cache disables caching for matching requests [OK]

Hint: Use fastcgi_no_cache to exclude requests from caching [OK]

Common Mistakes:

• Using fastcgi_cache_bypass alone to prevent caching
• Trying to conditionally set fastcgi_cache_valid
• Misusing fastcgi_cache_key for cache control