Proxy cache path configuration in Nginx - Commands & Configuration

Introduction

Sometimes web servers need to speed up responses by saving copies of requested content. Proxy cache path configuration in Nginx sets where and how these copies are stored on disk to serve future requests faster.

When you want to reduce load on your backend servers by caching responses.

When you want faster response times for repeated requests to the same content.

When you want to control disk space used for caching to avoid filling up the server.

When you want to organize cached files efficiently for quick access.

When you want to set limits on cache size and expiration to keep content fresh.

Config File - nginx.conf

nginx.conf

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

server {
    listen 80;
    location / {
        proxy_cache my_cache;
        proxy_pass http://backend_server;
        proxy_cache_valid 200 302 10m;
        proxy_cache_valid 404 1m;
    }
}

proxy_cache_path defines the directory where cached files are stored, the directory structure levels, the shared memory zone name and size, maximum cache size, and cache inactivity timeout.

Inside server, proxy_cache enables caching using the defined zone. proxy_pass forwards requests to the backend server. proxy_cache_valid sets how long responses with certain status codes are cached.

Commands

Check the Nginx configuration file syntax to ensure the proxy cache path settings are correct before reloading.

Terminal

sudo nginx -t

Expected Output

nginx: the configuration file /etc/nginx/nginx.conf syntax is ok

nginx: configuration file /etc/nginx/nginx.conf test is successful

Reload Nginx to apply the new proxy cache path configuration without stopping the server.

Terminal

sudo systemctl reload nginx

Expected Output

No output (command runs silently)

Verify that the cache directory exists and check its contents and permissions.

Terminal

ls -l /var/cache/nginx

Expected Output

total 0

-rw-r--r-- 1 nginx nginx 0 Jun 10 12:00 1

-rw-r--r-- 1 nginx nginx 0 Jun 10 12:00 2

→

-l - Show detailed list including permissions and timestamps

Key Concept

If you remember nothing else from this pattern, remember: proxy_cache_path sets where and how cached files are stored on disk for faster repeated responses.

Common Mistakes

Not creating or giving proper permissions to the cache directory.

Nginx cannot write cached files, so caching fails silently or with errors.

Create the cache directory with correct ownership (usually nginx user) and permissions before starting Nginx.

Using the same keys_zone name in multiple proxy_cache_path directives.

Nginx will fail to start because keys_zone names must be unique.

Use unique keys_zone names for each proxy_cache_path directive.

Not testing configuration with 'nginx -t' before reload.

Syntax errors cause Nginx reload to fail, leading to downtime.

Always run 'sudo nginx -t' to verify configuration before reloading.

Summary

Define proxy_cache_path in nginx.conf to specify cache storage location and parameters.

Test configuration syntax with 'nginx -t' before reloading Nginx.

Reload Nginx to apply changes and verify cache directory contents.

Practice

1. What is the main purpose of the proxy_cache_path directive in nginx?

easy

A. To set the maximum number of client connections

B. To specify the backend server IP address

C. To configure SSL certificates for secure connections

D. To define where and how cached files are stored

Solution

1. Step 1: Understand the role of proxy_cache_path

   The proxy_cache_path directive tells nginx where to save cached files and how to manage them.

2. Step 2: Compare with other options

   Options A, C, and D relate to connections, SSL, and backend servers, not caching.

3. Final Answer:

   To define where and how cached files are stored -> Option D

4. Quick Check:

   proxy_cache_path = cache storage location [OK]

Hint: proxy_cache_path sets cache storage location [OK]

Common Mistakes:

• Confusing proxy_cache_path with proxy_pass
• Thinking it sets connection limits
• Mixing it with SSL configuration

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

easy

A. proxy_cache_path /data/cache keys_zone=mycache:10m max_size=1g inactive=60m;

B. proxy_cache_path /data/cache keys_zone=mycache 10m max_size=1g inactive=60m

C. proxy_cache_path /data/cache keys_zone mycache:10m max_size=1g inactive=60m;

D. proxy_cache_path /data/cache keys_zone=mycache:10m max_size=1g inactive=60m

Solution

1. Step 1: Check syntax requirements for proxy_cache_path

   The directive requires a semicolon at the end and correct key-value pairs with colons where needed.

2. Step 2: Identify correct option

   proxy_cache_path /data/cache keys_zone=mycache:10m max_size=1g inactive=60m; has correct syntax with colon in keys_zone, key-value pairs, and ends with a semicolon.

3. Final Answer:

   proxy_cache_path /data/cache keys_zone=mycache:10m max_size=1g inactive=60m; -> Option A

4. Quick Check:

   Correct syntax ends with semicolon and uses colons properly [OK]

Hint: Always end proxy_cache_path with semicolon and use colons in keys_zone [OK]

Common Mistakes:

• Missing semicolon at the end
• Using space instead of colon in keys_zone
• Omitting equal signs in parameters

3. Given this nginx configuration snippet:

proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=mycache:10m max_size=500m inactive=30m;

What happens when a cached file is not accessed for 40 minutes?

medium

A. The cached file is refreshed automatically

B. The cached file remains because max_size is 500m

C. The cached file is removed because it is inactive longer than 30 minutes

D. The cached file is moved to a different cache zone

Solution

1. Step 1: Understand the inactive parameter

   The inactive=30m means cached files not accessed for 30 minutes are removed.

2. Step 2: Apply to 40 minutes inactivity

   Since 40 minutes > 30 minutes, the cached file will be removed.

3. Final Answer:

   The cached file is removed because it is inactive longer than 30 minutes -> Option C

4. Quick Check:

   inactive=30m means remove after 30 minutes inactivity [OK]

Hint: inactive time removes unused cache files after set duration [OK]

Common Mistakes:

• Confusing max_size with inactive time
• Assuming cache refresh happens automatically
• Thinking cache files move zones

4. You wrote this proxy cache path configuration:

proxy_cache_path /cache keys_zone=mycache 10m max_size=1g inactive=60m;

nginx fails to start. What is the error?

medium

A. Missing colon between keys_zone name and size

B. Invalid max_size value

C. Path /cache does not exist

D. inactive parameter should be in seconds

Solution

1. Step 1: Check keys_zone syntax

   The keys_zone requires a colon between the zone name and size, e.g., mycache:10m.

2. Step 2: Identify missing colon

   The config uses keys_zone=mycache 10m missing the colon, causing syntax error.

3. Final Answer:

   Missing colon between keys_zone name and size -> Option A

4. Quick Check:

   keys_zone syntax requires colon like mycache:10m [OK]

Hint: keys_zone must have colon between name and size [OK]

Common Mistakes:

• Forgetting colon in keys_zone
• Assuming inactive needs seconds
• Ignoring path existence errors

5. You want to configure nginx to cache responses in /var/cache/nginx with a 20MB keys zone, max cache size 2GB, and remove files inactive for 15 minutes. Which is the correct proxy_cache_path directive?

hard

A. proxy_cache_path /var/cache/nginx keys_zone=mycache:20m max_size=2gb inactive=15m;

B. proxy_cache_path /var/cache/nginx keys_zone=mycache:20m max_size=2g inactive=15m;

C. proxy_cache_path /var/cache/nginx keys_zone=mycache:20m max_size=1024m inactive=15m;

D. proxy_cache_path /var/cache/nginx keys_zone=mycache:20m max_size=2g inactive=900;

Solution

1. Step 1: Verify keys_zone size and path

   Keys zone size is 20m and path is /var/cache/nginx, both correct in all options.

2. Step 2: Check max_size and inactive syntax

   Max size should be 2g (gigabytes), inactive time 15m (minutes). proxy_cache_path /var/cache/nginx keys_zone=mycache:20m max_size=2g inactive=15m; uses correct units and syntax.

3. Step 3: Identify errors in other options

   proxy_cache_path /var/cache/nginx keys_zone=mycache:20m max_size=2gb inactive=15m; uses '2gb' (invalid unit), C uses 1024m (1GB not 2GB), D uses inactive=900 (seconds, but default is minutes and needs 's').

4. Final Answer:

   proxy_cache_path /var/cache/nginx keys_zone=mycache:20m max_size=2g inactive=15m; -> Option B

5. Quick Check:

   Use correct units: m for MB, g for GB, and time units with m for minutes [OK]

Hint: Use correct units: m for MB, g for GB, and m for minutes [OK]

Common Mistakes:

• Using invalid units like 'gb' instead of 'g'
• Confusing inactive time units
• Using seconds without 's' suffix