Advanced Level Module 5: Advanced Caching

📚 Learning Objectives

By the end of this module, you will: - Understand advanced caching strategies - Configure cache purging - Implement cache segmentation - Set up cache warming - Configure cache revalidation - Understand cache locking - Monitor cache performance

🎯 Advanced Caching Concepts

Advanced caching involves: - Cache purging and invalidation - Cache segmentation - Conditional caching - Cache warming - Cache revalidation - Cache locking

🔄 Cache Purging

Manual Cache Purging

# Allow purge from specific IPs
location ~ /purge(/.*) {
    allow 127.0.0.1;
    allow 192.168.1.0/24;
    deny all;

    proxy_cache_purge cache_zone $scheme$request_method$host$1;
}

Purge by Pattern

# Purge all cache for a domain
location ~ /purge_all {
    allow 127.0.0.1;
    deny all;

    # Custom Lua script or module needed
    # Or use external tool
}

Automatic Cache Invalidation

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

    # Map cache keys
    map $request_method $purge_method {
        PURGE 1;
        default 0;
    }

    server {
        location / {
            proxy_pass http://backend;
            proxy_cache my_cache;

            # Handle PURGE method
            proxy_cache_bypass $purge_method;
            proxy_no_cache $purge_method;

            # Purge on POST/PUT/DELETE
            proxy_cache_bypass $request_method;
            proxy_no_cache $request_method;
        }
    }
}

📊 Cache Segmentation

Separate Cache Zones

http {
    # Cache for static content
    proxy_cache_path /var/cache/nginx/static levels=1:2 
                     keys_zone=static_cache:50m max_size=5g 
                     inactive=7d use_temp_path=off;

    # Cache for dynamic content
    proxy_cache_path /var/cache/nginx/dynamic levels=1:2 
                     keys_zone=dynamic_cache:50m max_size=2g 
                     inactive=1h use_temp_path=off;

    # Cache for API responses
    proxy_cache_path /var/cache/nginx/api levels=1:2 
                     keys_zone=api_cache:10m max_size=500m 
                     inactive=10m use_temp_path=off;

    server {
        # Static content - long cache
        location ~* \.(jpg|jpeg|png|gif|css|js)$ {
            proxy_pass http://backend;
            proxy_cache static_cache;
            proxy_cache_valid 200 7d;
        }

        # Dynamic content - short cache
        location / {
            proxy_pass http://backend;
            proxy_cache dynamic_cache;
            proxy_cache_valid 200 1h;
        }

        # API - very short cache
        location /api/ {
            proxy_pass http://backend;
            proxy_cache api_cache;
            proxy_cache_valid 200 10m;
        }
    }
}

Cache by User Role

http {
    proxy_cache_path /var/cache/nginx levels=1:2 
                     keys_zone=my_cache:10m max_size=1g;

    map $http_authorization $cache_key {
        default $scheme$request_method$host$request_uri;
        "~Bearer.*" $scheme$request_method$host$request_uri$http_authorization;
    }

    server {
        location / {
            proxy_pass http://backend;
            proxy_cache my_cache;
            proxy_cache_key $cache_key;
        }
    }
}

⏰ Cache Revalidation

Stale-While-Revalidate

location / {
    proxy_pass http://backend;
    proxy_cache my_cache;

    # Serve stale content while revalidating
    proxy_cache_use_stale error timeout updating http_500 http_502 http_503 http_504;
    proxy_cache_background_update on;
    proxy_cache_revalidate on;
}

How it works: - Serves stale content immediately - Updates cache in background - Next request gets fresh content

Conditional Requests (ETag/Last-Modified)

location / {
    proxy_pass http://backend;
    proxy_cache my_cache;

    # Use ETag and Last-Modified
    proxy_cache_revalidate on;

    # Pass conditional headers to backend
    proxy_set_header If-None-Match $http_if_none_match;
    proxy_set_header If-Modified-Since $http_if_modified_since;
}

🔒 Cache Locking

Prevent Cache Stampede

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

    proxy_cache_lock on;          # Enable cache locking
    proxy_cache_lock_timeout 5s;  # Lock timeout
    proxy_cache_lock_age 10s;     # Lock age
}

Benefits: - Prevents multiple requests for same resource - Reduces backend load - First request fetches, others wait

🔥 Cache Warming

Pre-populate Cache

# Warm cache by requesting common pages
curl http://example.com/
curl http://example.com/about
curl http://example.com/products
curl http://example.com/contact

# Or with script
#!/bin/bash
URLS=(
    "http://example.com/"
    "http://example.com/about"
    "http://example.com/products"
)

for url in "${URLS[@]}"; do
    curl -s "$url" > /dev/null
done

Scheduled Cache Warming

# Add to crontab
*/5 * * * * /usr/local/bin/warm_cache.sh

📋 Advanced Cache Configuration

Complete Advanced Setup

http {
    # Main cache zone
    proxy_cache_path /var/cache/nginx/main levels=1:2 
                     keys_zone=main_cache:100m max_size=10g 
                     inactive=24h use_temp_path=off;

    # Static cache zone
    proxy_cache_path /var/cache/nginx/static levels=1:2 
                     keys_zone=static_cache:50m max_size=5g 
                     inactive=7d use_temp_path=off;

    # API cache zone
    proxy_cache_path /var/cache/nginx/api levels=1:2 
                     keys_zone=api_cache:10m max_size=500m 
                     inactive=10m use_temp_path=off;

    # Cache key variables
    map $request_method $cache_method {
        GET HEAD "";
        default "no_cache";
    }

    map $http_authorization $is_authenticated {
        default "";
        "~Bearer.*" "authenticated";
    }

    server {
        listen 80;
        server_name example.com;

        # Static content
        location ~* \.(jpg|jpeg|png|gif|ico|css|js|svg|woff|woff2)$ {
            proxy_pass http://backend;

            proxy_cache static_cache;
            proxy_cache_key "$scheme$request_method$host$request_uri";
            proxy_cache_valid 200 7d;
            proxy_cache_valid 404 1h;

            # Headers
            add_header X-Cache-Status $upstream_cache_status;
            add_header X-Cache-Key $request_uri;

            # Stale content
            proxy_cache_use_stale error timeout updating;
            proxy_cache_background_update on;
        }

        # API endpoints
        location /api/ {
            proxy_pass http://backend;

            proxy_cache api_cache;
            proxy_cache_key "$scheme$request_method$host$request_uri$is_authenticated";
            proxy_cache_valid 200 10m;
            proxy_cache_valid 404 1m;

            # Cache locking
            proxy_cache_lock on;
            proxy_cache_lock_timeout 5s;

            # Conditional requests
            proxy_cache_revalidate on;

            # Bypass cache for authenticated requests
            proxy_cache_bypass $is_authenticated;
            proxy_no_cache $is_authenticated;

            # Headers
            add_header X-Cache-Status $upstream_cache_status;
        }

        # Dynamic content
        location / {
            proxy_pass http://backend;

            proxy_cache main_cache;
            proxy_cache_key "$scheme$request_method$host$request_uri";
            proxy_cache_valid 200 1h;
            proxy_cache_valid 302 10m;
            proxy_cache_valid 404 5m;

            # Method-based caching
            proxy_cache_bypass $cache_method;
            proxy_no_cache $cache_method;

            # Stale while revalidate
            proxy_cache_use_stale error timeout updating http_500 http_502 http_503;
            proxy_cache_background_update on;
            proxy_cache_revalidate on;

            # Cache locking
            proxy_cache_lock on;
            proxy_cache_lock_timeout 5s;

            # Headers
            add_header X-Cache-Status $upstream_cache_status;
            add_header X-Cache-Key $request_uri;
            add_header Cache-Control "public, max-age=3600";
        }

        # Cache purge endpoint
        location ~ /purge(/.*) {
            allow 127.0.0.1;
            allow 192.168.1.0/24;
            deny all;

            proxy_cache_purge main_cache $scheme$request_method$host$1;
        }
    }
}

📊 Cache Monitoring

Cache Statistics

# Custom log format with cache info
log_format cache_log '$remote_addr - $remote_user [$time_local] '
                     '"$request" $status $body_bytes_sent '
                     'cache: $upstream_cache_status '
                     'time: $request_time';

Monitor Cache Hit Ratio

# Count cache hits vs misses
sudo awk '{print $NF}' /var/log/nginx/access.log | grep cache | sort | uniq -c

# Calculate hit ratio
hits=$(sudo grep -c "cache: HIT" /var/log/nginx/access.log)
misses=$(sudo grep -c "cache: MISS" /var/log/nginx/access.log)
total=$((hits + misses))
ratio=$(echo "scale=2; $hits * 100 / $total" | bc)
echo "Cache hit ratio: ${ratio}%"

Cache Size Monitoring

# Check cache directory size
du -sh /var/cache/nginx

# Count cached files
find /var/cache/nginx -type f | wc -l

# Find largest cache files
find /var/cache/nginx -type f -exec ls -lh {} \; | awk '{print $5, $9}' | sort -hr | head

🔍 Cache Debugging

Enable Cache Debugging

error_log /var/log/nginx/cache.log debug;

Debug Headers

location / {
    proxy_pass http://backend;
    proxy_cache my_cache;

    # Debug headers
    add_header X-Cache-Status $upstream_cache_status;
    add_header X-Cache-Key $request_uri;
    add_header X-Cache-Valid $upstream_cache_valid;
}

📝 Exercises

1. Set up cache purging mechanism
2. Create separate cache zones for different content types
3. Implement stale-while-revalidate
4. Enable cache locking
5. Set up cache warming script
6. Monitor cache hit ratio
7. Configure conditional cache revalidation
8. Test cache invalidation

✅ Checklist

• [ ] Understand advanced caching concepts
• [ ] Can configure cache purging
• [ ] Can segment caches
• [ ] Understand cache revalidation
• [ ] Can implement cache locking
• [ ] Can set up cache warming
• [ ] Can monitor cache performance
• [ ] Can debug cache issues

➡️ Next Steps

Proceed to Module 6: HTTP/2 and HTTP/3 to learn about modern HTTP protocols.