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Bài học về Caching trong Nginx - browser caching với expires và Cache-Control headers, proxy caching, FastCGI caching cho PHP, cache keys và zones. Hướng dẫn cache purging, bypass strategies và optimization techniques. Bao gồm examples thực tế để tăng performance và giảm load.

Nginx từ Cơ bản đến Nâng cao

Phần 2: Reverse Proxy & Load Balancing

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1. Browser Caching với Expires và Cache-Control Headers

Browser caching lưu trữ files tại client browser, giảm số requests đến server và tăng tốc độ load.

1.1. Expires Header

Expires header chỉ định thời điểm cụ thể khi cache hết hạn.

Cú pháp cơ bản:

location ~* \.(jpg|jpeg|png|gif|ico)$ {
    expires 30d;  # Cache 30 ngày
}

Các giá trị expires:

server {
    listen 80;
    server_name example.com;
    root /var/www/html;
# Images - cache lâu
location ~* \.(jpg|jpeg|png|gif|ico|svg|webp)$ {
    expires 1y;  # 1 năm
    add_header Cache-Control "public, immutable";
}

# CSS và JavaScript - cache trung bình
location ~* \.(css|js)$ {
    expires 1M;  # 1 tháng
    add_header Cache-Control "public";
}

# HTML - cache ngắn hoặc no-cache
location ~* \.html$ {
    expires 1h;  # 1 giờ
    add_header Cache-Control "public, must-revalidate";
}

# API responses - không cache
location /api/ {
    expires -1;  # Không cache
    add_header Cache-Control "no-cache, no-store, must-revalidate";
}

}

Time units:

expires 1s;    # 1 second
expires 5m;    # 5 minutes
expires 2h;    # 2 hours
expires 7d;    # 7 days
expires 3M;    # 3 months (30 days)
expires 1y;    # 1 year
expires -1;    # Không cache (Cache-Control: no-cache)
expires epoch; # Expires: Thu, 01 Jan 1970 00:00:01 GMT
expires max;   # Expires: Thu, 31 Dec 2037 23:55:55 GMT
expires off;   # Không set Expires header

Ví dụ chi tiết:

server {
listen 80;
server_name cdn.example.com;
root /var/www/cdn;
# Versioned assets - cache vĩnh viễn
location ~* \.(jpg|jpeg|png|gif|ico|css|js|woff|woff2|ttf)$ {
    # Chỉ áp dụng cho files có version trong tên
    # vd: style.v1.2.3.css, app.20240101.js
    if ($uri ~ "\.v[0-9]+\.|\.v?\d{8,}\.") {
        expires max;
        add_header Cache-Control "public, immutable";
    }
    
    # Files không có version
    expires 1M;
    add_header Cache-Control "public";
}

# Videos - cache lâu nhưng có thể revalidate
location ~* \.(mp4|webm|ogg|avi)$ {
    expires 6M;
    add_header Cache-Control "public, max-age=15552000";
}

# Documents - cache ngắn
location ~* \.(pdf|doc|docx|xls|xlsx)$ {
    expires 1d;
    add_header Cache-Control "public, max-age=86400";
}

}

1.2. Cache-Control Header

Cache-Control là modern alternative cho Expires, flexible hơn.

Cache-Control directives:

# public: Có thể cache bởi browser và intermediate caches add_header Cache-Control "public"; private: Chỉ browser cache, không cache ở proxies add_header Cache-Control "private"; no-cache: Phải revalidate trước khi dùng cache add_header Cache-Control "no-cache"; no-store: Không cache gì cả add_header Cache-Control "no-store"; max-age: Cache duration (seconds) add_header Cache-Control "public, max-age=31536000"; s-maxage: Max-age cho shared caches (CDN, proxies) add_header Cache-Control "public, max-age=3600, s-maxage=86400"; must-revalidate: Phải revalidate khi stale add_header Cache-Control "public, max-age=3600, must-revalidate"; immutable: Content không bao giờ thay đổi add_header Cache-Control "public, max-age=31536000, immutable"; no-transform: Không cho phép transform content

add_header Cache-Control "public, no-transform";

Combining directives:

server {
listen 80;
server_name example.com;
# Static assets với versioning - immutable
location ~* /static/.*\.(css|js)$ {
    expires 1y;
    add_header Cache-Control "public, max-age=31536000, immutable";
}

# Images - public, long cache
location ~* \.(jpg|png|gif|svg)$ {
    expires 6M;
    add_header Cache-Control "public, max-age=15552000";
}

# HTML - cache ngắn với revalidation
location ~* \.html$ {
    expires 10m;
    add_header Cache-Control "public, max-age=600, must-revalidate";
}

# User-specific content - private
location /dashboard/ {
    add_header Cache-Control "private, max-age=300";
}

# Sensitive data - no cache
location /account/ {
    add_header Cache-Control "private, no-cache, no-store, must-revalidate";
    add_header Pragma "no-cache";
    add_header Expires "0";
}

}

1.3. Conditional Caching

map $sent_http_content_type $expires {
default                    off;
text/html                  1h;
text/css                   1M;
application/javascript     1M;
~image/                    1y;
application/pdf            7d;
~font/                     1y;
}
server {
listen 80;
server_name example.com;
expires $expires;

# Override cho specific paths
location /news/ {
    expires 5m;
    add_header Cache-Control "public, max-age=300";
}

}

Cache dựa trên file extension:

server {
listen 80;
root /var/www/html;
# Map file extensions to cache duration
location / {
    if ($request_uri ~* "\.(jpg|jpeg|png|gif|ico)$") {
        expires 1y;
        add_header Cache-Control "public, immutable";
    }
    
    if ($request_uri ~* "\.(css|js)$") {
        expires 1M;
        add_header Cache-Control "public";
    }
    
    if ($request_uri ~* "\.html$") {
        expires 1h;
        add_header Cache-Control "public, must-revalidate";
    }
    
    try_files $uri $uri/ =404;
}

}

1.4. ETag và Last-Modified

server {
listen 80;
server_name example.com;
# Enable ETag
etag on;

# Enable Last-Modified header
if_modified_since before;

location / {
    root /var/www/html;
    
    # Browser sẽ gửi If-None-Match (ETag) hoặc If-Modified-Since
    # Nginx trả về 304 Not Modified nếu file không thay đổi
}

}

Example với conditional requests:

server {
listen 80;
server_name api.example.com;
location /api/data {
    proxy_pass http://backend;
    
    # Pass conditional headers to backend
    proxy_set_header If-Modified-Since $http_if_modified_since;
    proxy_set_header If-None-Match $http_if_none_match;
    
    # Backend returns 304 if not modified
    # Nginx forwards 304 to client
}

}

2. Proxy Caching Cơ bản

Proxy caching lưu trữ responses từ backend servers, giảm load và response time.

2.1. Cấu hình Proxy Cache Zone

# Define cache path và settings (trong http context)
http {
proxy_cache_path /var/cache/nginx/proxy
levels=1:2
keys_zone=my_cache:10m
max_size=1g
inactive=60m
use_temp_path=off;
server {
    listen 80;
    server_name example.com;
    
    location / {
        proxy_pass http://backend;
        
        # Enable caching
        proxy_cache my_cache;
        
        # Cache durations
        proxy_cache_valid 200 302 10m;
        proxy_cache_valid 404 1m;
        proxy_cache_valid any 5m;
        
        # Add cache status header
        add_header X-Cache-Status $upstream_cache_status;
    }
}

}

Giải thích parameters:

proxy_cache_path /var/cache/nginx/proxy    # Đường dẫn lưu cache
levels=1:2                              # Cấu trúc thư mục (tối ưu I/O)
keys_zone=my_cache:10m                  # Tên zone và size của shared memory
max_size=1g                             # Max cache size trên disk
inactive=60m                            # Xóa cache không dùng sau 60 phút
use_temp_path=off;                      # Ghi trực tiếp vào cache path

Levels explained:

levels=1:2 tạo structure: /var/cache/nginx/proxy/ ├── a/ │ ├── 3c/ │ │ └── abc123...def │ └── 7f/ └── b/ └── 2d/

First level: 1 character (a, b, c...) Second level: 2 characters (3c, 7f, 2d...)

2.2. Cache Status Values

$upstream_cache_status có thể là:


MISS       : Request không có trong cache, fetched từ backend


HIT        : Request served từ cache


EXPIRED    : Cache entry expired, fetched từ backend


STALE      : Serving stale content (nếu configured)


UPDATING   : Cache đang update từ backend


REVALIDATED: Cache revalidated với backend (304)


BYPASS     : Cache bị bypass (theo config)

Logging cache status:

http {
log_format cache_log '$remote_addr - [$time_local] '
'"$request" $status '
'Cache: $upstream_cache_status '
'Time: $upstream_response_time';
server {
listen 80;
access_log /var/log/nginx/cache.log cache_log;
  location / {
      proxy_pass http://backend;
      proxy_cache my_cache;
      
      add_header X-Cache-Status $upstream_cache_status always;
  }

}
}

2.3. Cache Key

Cache key xác định uniqueness của cached items.

Default cache key:

proxy_cache_key $scheme$proxy_host$request_uri;


Example:
http://example.com/page?id=1
Key: httpexample.com/page?id=1

Custom cache keys:

location / { proxy_pass http://backend; proxy_cache my_cache; # Include request method proxy_cache_key "$scheme$request_method$host$request_uri"; # Include specific headers # proxy_cache_key "$scheme$host$request_uri$http_accept_language"; # Include cookies # proxy_cache_key "$scheme$host$request_uri$cookie_session";

}

Example với user-specific caching:

map $cookie_user_id $cache_user {
default $cookie_user_id;
"" "anonymous";
}
server {
location /api/ {
proxy_pass http://backend;
proxy_cache user_cache;
    # Different cache per user
    proxy_cache_key "$scheme$host$request_uri$cache_user";
}

}

2.4. Cache Methods và Conditions

server { listen 80; location / { proxy_pass http://backend; proxy_cache my_cache; # Chỉ cache GET và HEAD methods proxy_cache_methods GET HEAD; # Cache durations dựa trên status code proxy_cache_valid 200 301 302 10m; proxy_cache_valid 404 1m; proxy_cache_valid any 5m; # Minimum số requests trước khi cache proxy_cache_min_uses 3; # Cache kể cả khi backend error proxy_cache_use_stale error timeout updating http_500 http_502 http_503 http_504; # Lock để tránh cache stampede proxy_cache_lock on; proxy_cache_lock_timeout 5s; proxy_cache_lock_age 5s; }

}

proxy_cache_use_stale explained:

proxy_cache_use_stale error timeout updating http_500 http_502 http_503 http_504; Serve stale cache khi: - error: Lỗi kết nối đến backend - timeout: Backend timeout - updating: Cache đang được update (tránh stampede) - http_500/502/503/504: Backend trả về error codes

2.5. Complete Proxy Cache Example

http {
# Define multiple cache zones
proxy_cache_path /var/cache/nginx/static
levels=1:2
keys_zone=static_cache:10m
max_size=500m
inactive=60m
use_temp_path=off;
proxy_cache_path /var/cache/nginx/api
                 levels=1:2
                 keys_zone=api_cache:10m
                 max_size=200m
                 inactive=10m
                 use_temp_path=off;

upstream backend {
    server backend1.example.com:8080;
    server backend2.example.com:8080;
}

server {
    listen 80;
    server_name example.com;
    
    # Static content cache
    location ~* \.(jpg|jpeg|png|gif|ico|css|js)$ {
        proxy_pass http://backend;
        proxy_cache static_cache;
        
        proxy_cache_valid 200 30d;
        proxy_cache_valid 404 1h;
        
        proxy_cache_use_stale error timeout updating http_500 http_502 http_503 http_504;
        proxy_cache_lock on;
        
        expires 30d;
        add_header Cache-Control "public, immutable";
        add_header X-Cache-Status $upstream_cache_status;
    }
    
    # API cache
    location /api/ {
        proxy_pass http://backend;
        proxy_cache api_cache;
        
        proxy_cache_valid 200 5m;
        proxy_cache_valid 404 1m;
        
        proxy_cache_key "$scheme$request_method$host$request_uri$http_authorization";
        proxy_cache_methods GET HEAD;
        proxy_cache_min_uses 2;
        
        proxy_cache_use_stale error timeout updating;
        proxy_cache_lock on;
        
        add_header X-Cache-Status $upstream_cache_status;
    }
    
    # No cache for user-specific content
    location /account/ {
        proxy_pass http://backend;
        proxy_cache off;
        proxy_no_cache 1;
        proxy_cache_bypass 1;
    }
}

}

3. FastCGI Caching

FastCGI caching dùng cho dynamic content như PHP applications.

3.1. FastCGI Cache Configuration

http {
# Define FastCGI cache zone
fastcgi_cache_path /var/cache/nginx/fastcgi
levels=1:2
keys_zone=php_cache:10m
max_size=500m
inactive=60m
use_temp_path=off;
# Cache key
fastcgi_cache_key "$scheme$request_method$host$request_uri";

server {
    listen 80;
    server_name example.com;
    root /var/www/html;
    index index.php index.html;
    
    location ~ \.php$ {
        fastcgi_pass unix:/var/run/php/php8.1-fpm.sock;
        fastcgi_index index.php;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        
        # Enable FastCGI cache
        fastcgi_cache php_cache;
        
        # Cache valid durations
        fastcgi_cache_valid 200 60m;
        fastcgi_cache_valid 404 10m;
        
        # Cache use stale
        fastcgi_cache_use_stale error timeout updating invalid_header http_500;
        
        # Cache locking
        fastcgi_cache_lock on;
        fastcgi_cache_lock_timeout 5s;
        
        # Minimum uses before caching
        fastcgi_cache_min_uses 2;
        
        # Add cache status header
        add_header X-FastCGI-Cache $upstream_cache_status;
    }
}

}

3.2. WordPress với FastCGI Cache

http {
fastcgi_cache_path /var/cache/nginx/wordpress
levels=1:2
keys_zone=wordpress:100m
max_size=1g
inactive=60m
use_temp_path=off;
fastcgi_cache_key "$scheme$request_method$host$request_uri";

server {
    listen 80;
    server_name blog.example.com;
    root /var/www/wordpress;
    index index.php;
    
    # Set cache bypass conditions
    set $skip_cache 0;
    
    # POST requests và URLs với query strings
    if ($request_method = POST) {
        set $skip_cache 1;
    }
    
    if ($query_string != "") {
        set $skip_cache 1;
    }
    
    # Don't cache URIs containing the following segments
    if ($request_uri ~* "/wp-admin/|/xmlrpc.php|wp-.*.php|/feed/|index.php|sitemap(_index)?.xml") {
        set $skip_cache 1;
    }
    
    # Don't cache logged in users or recent commenters
    if ($http_cookie ~* "comment_author|wordpress_[a-f0-9]+|wp-postpass|wordpress_logged_in") {
        set $skip_cache 1;
    }
    
    location / {
        try_files $uri $uri/ /index.php?$args;
    }
    
    location ~ \.php$ {
        try_files $uri =404;
        
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        fastcgi_pass unix:/var/run/php/php8.1-fpm.sock;
        fastcgi_index index.php;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        fastcgi_param PATH_INFO $fastcgi_path_info;
        
        # FastCGI cache settings
        fastcgi_cache wordpress;
        fastcgi_cache_valid 200 60m;
        fastcgi_cache_valid 404 10m;
        
        fastcgi_cache_bypass $skip_cache;
        fastcgi_no_cache $skip_cache;
        
        fastcgi_cache_use_stale error timeout updating invalid_header http_500 http_503;
        fastcgi_cache_lock on;
        
        # Headers
        add_header X-FastCGI-Cache $upstream_cache_status;
        add_header Cache-Control "public, max-age=3600";
    }
    
    # Cache static files
    location ~* \.(jpg|jpeg|png|gif|ico|css|js|svg|woff|woff2)$ {
        expires 30d;
        add_header Cache-Control "public, immutable";
        access_log off;
    }
    
    # Deny access to hidden files
    location ~ /\. {
        deny all;
        access_log off;
        log_not_found off;
    }
}

}

3.3. Drupal với FastCGI Cache

http {
fastcgi_cache_path /var/cache/nginx/drupal
levels=1:2
keys_zone=drupal:100m
max_size=2g
inactive=60m
use_temp_path=off;
server {
    listen 80;
    server_name drupal.example.com;
    root /var/www/drupal;
    
    # Cache bypass conditions
    set $skip_cache 0;
    
    if ($request_method = POST) {
        set $skip_cache 1;
    }
    
    if ($query_string != "") {
        set $skip_cache 1;
    }
    
    if ($request_uri ~* "^/(admin|user|cart|checkout)/") {
        set $skip_cache 1;
    }
    
    if ($http_cookie ~* "SESS") {
        set $skip_cache 1;
    }
    
    location / {
        try_files $uri /index.php?$query_string;
    }
    
    location ~ '\.php$|^/update.php' {
        fastcgi_pass unix:/var/run/php/php8.1-fpm.sock;
        fastcgi_split_path_info ^(.+?\.php)(|/.*)$;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        
        fastcgi_cache drupal;
        fastcgi_cache_valid 200 301 302 5m;
        fastcgi_cache_valid 404 1m;
        
        fastcgi_cache_bypass $skip_cache;
        fastcgi_no_cache $skip_cache;
        
        fastcgi_cache_use_stale error timeout updating invalid_header http_500;
        fastcgi_cache_lock on;
        
        add_header X-FastCGI-Cache $upstream_cache_status;
    }
    
    location ~ ^/sites/.*/files/styles/ {
        try_files $uri @rewrite;
        expires 30d;
        add_header Cache-Control "public, immutable";
    }
}

}

3.4. Custom PHP Application với Cache

http {
fastcgi_cache_path /var/cache/nginx/app
levels=1:2
keys_zone=app_cache:50m
max_size=1g
inactive=30m
use_temp_path=off;
# Custom cache key with user context
map $http_cookie $user_context {
    default "anonymous";
    ~*user_id=(?&lt;uid&gt;[^;]+) $uid;
}

server {
    listen 80;
    server_name app.example.com;
    root /var/www/app/public;
    
    # Cache bypass cho authenticated users
    set $skip_cache 0;
    
    if ($http_cookie ~* "logged_in") {
        set $skip_cache 1;
    }
    
    if ($request_uri ~* "/(api|admin)/") {
        set $skip_cache 1;
    }
    
    location ~ \.php$ {
        fastcgi_pass unix:/var/run/php/php8.1-fpm.sock;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        
        # Custom cache key
        fastcgi_cache_key "$scheme$request_method$host$request_uri$user_context";
        
        fastcgi_cache app_cache;
        fastcgi_cache_valid 200 10m;
        fastcgi_cache_valid 404 1m;
        
        fastcgi_cache_bypass $skip_cache;
        fastcgi_no_cache $skip_cache;
        
        fastcgi_cache_use_stale error timeout updating;
        fastcgi_cache_lock on;
        fastcgi_cache_min_uses 3;
        
        # Custom headers
        add_header X-Cache-Status $upstream_cache_status;
        add_header X-Cache-Key "$scheme$request_method$host$request_uri$user_context";
    }
}

}

4. Cache Keys và Cache Zones

4.1. Cache Zones Configuration

http {
# Static content cache - large, long-lived
proxy_cache_path /var/cache/nginx/static
levels=1:2
keys_zone=static:100m
max_size=5g
inactive=7d
use_temp_path=off;
# API cache - smaller, short-lived
proxy_cache_path /var/cache/nginx/api
                 levels=1:2
                 keys_zone=api:50m
                 max_size=1g
                 inactive=1h
                 use_temp_path=off;

# User-specific cache
proxy_cache_path /var/cache/nginx/user
                 levels=1:2
                 keys_zone=user:50m
                 max_size=2g
                 inactive=30m
                 use_temp_path=off;

# HTML pages cache
proxy_cache_path /var/cache/nginx/pages
                 levels=1:2
                 keys_zone=pages:20m
                 max_size=500m
                 inactive=2h
                 use_temp_path=off;

}

Zone size calculation:

keys_zone size stores cache metadata:

1MB ≈ 8000 keys
10MB ≈ 80,000 keys
100MB ≈ 800,000 keys

Max cache size stores actual content:

Set based on available disk space
Monitor /var/cache/nginx disk usage

4.2. Advanced Cache Keys

Cache by device type:

map $http_user_agent $device {
default desktop;
~mobile mobile;
~tablet tablet;
}

server {
location / {
proxy_pass http://backend;
proxy_cache my_cache;
    # Different cache per device
    proxy_cache_key "$scheme$host$request_uri$device";
    
    add_header X-Device $device;
    add_header X-Cache-Status $upstream_cache_status;
}

}

Cache by accept headers:

map $http_accept $content_type_key {
default "html";
~application/json "json";
~application/xml "xml";
}
server {
location /api/ {
proxy_pass http://backend;
proxy_cache api_cache;
    # Different cache per content type
    proxy_cache_key "$scheme$host$request_uri$content_type_key";
}

}

Cache by language:

map $http_accept_language $lang {
default en;
~^vi vi;
~^ja ja;
~*^zh zh;
}
server {
location / {
proxy_pass http://backend;
proxy_cache my_cache;
    # Different cache per language
    proxy_cache_key "$scheme$host$request_uri$lang";
    
    add_header Content-Language $lang;
}

}

Cache by geo location:

geo $country {
default US;
192.168.1.0/24 VN;
10.0.0.0/8 JP;
}
server {
location / {
proxy_pass http://backend;
proxy_cache my_cache;
    # Different cache per country
    proxy_cache_key "$scheme$host$request_uri$country";
}

}

Complex cache key:

map $http_cookie $user_segment {
default "guest";
~premium=1 "premium";
~vip=1 "vip";
}
server {
location /api/ {
proxy_pass http://backend;
proxy_cache api_cache;
    # Cache key combining multiple factors
    proxy_cache_key "$scheme$host$request_uri$user_segment$device$lang";
    
    add_header X-Cache-Key-Components "segment:$user_segment|device:$device|lang:$lang";
}

}

4.3. Cache Hierarchy

http {
# L1 Cache - Memory (small, fast)
proxy_cache_path /dev/shm/nginx
levels=1
keys_zone=l1_cache:10m
max_size=100m
inactive=5m
use_temp_path=off;
# L2 Cache - SSD (medium, fast)
proxy_cache_path /var/cache/nginx/l2
                 levels=1:2
                 keys_zone=l2_cache:50m
                 max_size=5g
                 inactive=1h
                 use_temp_path=off;

# L3 Cache - HDD (large, slower)
proxy_cache_path /mnt/cache/nginx/l3
                 levels=1:2
                 keys_zone=l3_cache:100m
                 max_size=50g
                 inactive=7d
                 use_temp_path=off;

server {
    location /api/hot/ {
        # Frequently accessed - L1 cache
        proxy_pass http://backend;
        proxy_cache l1_cache;
        proxy_cache_valid 200 5m;
    }
    
    location /api/warm/ {
        # Moderately accessed - L2 cache
        proxy_pass http://backend;
        proxy_cache l2_cache;
        proxy_cache_valid 200 1h;
    }
    
    location /api/cold/ {
        # Rarely accessed - L3 cache
        proxy_pass http://backend;
        proxy_cache l3_cache;
        proxy_cache_valid 200 1d;
    }
}

}

5. Cache Purging và Bypass

5.1. Cache Bypass

server {
listen 80;
# Bypass cache với special header
location / {
    proxy_pass http://backend;
    proxy_cache my_cache;
    
    # Bypass if X-No-Cache header present
    proxy_cache_bypass $http_x_no_cache;
    
    # Or bypass with cookie
    proxy_cache_bypass $cookie_nocache;
    
    # Or bypass with argument
    proxy_cache_bypass $arg_nocache;
}

}

Multiple bypass conditions:

server {
location / {
proxy_pass http://backend;
proxy_cache my_cache;
    # Set bypass conditions
    set $cache_bypass 0;
    
    # Bypass for specific cookies
    if ($http_cookie ~* "admin_logged_in") {
        set $cache_bypass 1;
    }
    
    # Bypass for specific URLs
    if ($request_uri ~* "^/(admin|dashboard)/") {
        set $cache_bypass 1;
    }
    
    # Bypass for POST requests
    if ($request_method = POST) {
        set $cache_bypass 1;
    }
    
    # Apply bypass
    proxy_cache_bypass $cache_bypass;
    proxy_no_cache $cache_bypass;
}

}

Bypass với query parameter:

server {
location / {
proxy_pass http://backend;
proxy_cache my_cache;
    # ?nocache=1 → bypass cache
    proxy_cache_bypass $arg_nocache;
    
    # ?refresh=1 → refresh cache
    proxy_cache_bypass $arg_refresh;
    
    add_header X-Cache-Bypass $arg_nocache;
}

}
Usage:
Normal: http://example.com/page
Bypass: http://example.com/page?nocache=1
Refresh: http://example.com/page?refresh=1

5.2. Cache Purging (Nginx Plus / Third-party module)

Nginx Plus purge:

# Nginx Plus only
map $request_method $purge_method {
PURGE 1;
default 0;
}
server {
location / {
proxy_pass http://backend;
proxy_cache my_cache;
proxy_cache_purge $purge_method;
}
}
Usage:
curl -X PURGE http://example.com/page

Cache purge với open source module:

# Install ngx_cache_purge module Ubuntu/Debian sudo apt install libnginx-mod-http-cache-purge CentOS - compile from source

http {
proxy_cache_path /var/cache/nginx/proxy
levels=1:2
keys_zone=my_cache:10m;
server {
    listen 80;
    
    location / {
        proxy_pass http://backend;
        proxy_cache my_cache;
        proxy_cache_key "$scheme$host$request_uri";
    }
    
    # Purge location
    location ~ /purge(/.*) {
        allow 127.0.0.1;
        allow 10.0.0.0/8;
        deny all;
        
        proxy_cache_purge my_cache "$scheme$host$1";
    }
}

}
Usage:
curl http://example.com/purge/page-to-clear

Manual cache purging:

#!/bin/bash
purge_cache.sh - Manual cache purge script
CACHE_DIR="/var/cache/nginx"
CACHE_ZONE="my_cache"
Purge all cache
purge_all() {
echo "Purging all cache..."
sudo rm -rf ${CACHE_DIR}/${CACHE_ZONE}/*
echo "Cache purged!"
}
Purge specific URL
purge_url() {
local url=$1
local cache_key=$(echo -n "$url" | md5sum | awk '{print $1}')
local cache_path=$(find ${CACHE_DIR}/${CACHE_ZONE} -name "${cache_key}")
if [ -n "$cache_path" ]; then
    echo "Purging cache for: $url"
    sudo rm -f $cache_path
    echo "Purged: $cache_path"
else
    echo "No cache found for: $url"
fi

}
Purge by pattern
purge_pattern() {
local pattern=$1
echo "Purging cache matching: $pattern"
sudo find ${CACHE_DIR}/${CACHE_ZONE} -type f -name "${pattern}" -delete
echo "Done!"
}
case "$1" in
all)
purge_all
;;
url)
purge_url "$2"
;;
pattern)
purge_pattern "$2"
;;
*)
echo "Usage: $0 {all|url <url>|pattern <pattern>}"
exit 1
;;
esac

Cache warmup script:

#!/bin/bash
cache_warmup.sh - Warm up cache
URLS=(
"http://example.com/"
"http://example.com/products"
"http://example.com/about"
"http://example.com/contact"
)
echo "Starting cache warmup..."
for url in "${URLS[@]}"; do
echo "Warming up: $url"
curl -s -o /dev/null -w "Status: %{http_code}, Time: %{time_total}s\n" "$url"
sleep 0.5
done
echo "Cache warmup complete!"

5.3. Selective Cache Invalidation

# API để invalidate cache
server {
listen 80;
server_name example.com;
location / {
    proxy_pass http://backend;
    proxy_cache my_cache;
    proxy_cache_valid 200 10m;
}

# Cache invalidation endpoint
location /api/cache/invalidate {
    allow 127.0.0.1;
    allow 10.0.0.0/8;
    deny all;
    
    content_by_lua_block {
        local pattern = ngx.var.arg_pattern
        if pattern then
            -- Invalidate cache matching pattern
            -- Implementation depends on cache module
            ngx.say("Cache invalidated for pattern: ", pattern)
        else
            ngx.say("Pattern required")
        end
    }
}

}
Usage:
curl "http://example.com/api/cache/invalidate?pattern=/products/*"

6. Bài tập Thực hành

Bài tập 1: Browser Caching

Setup static file server
Configure expires headers:
- Images: 1 year
- CSS/JS: 1 month
- HTML: 1 hour
Test với browser DevTools (Network tab)
Verify cache headers

Bài tập 2: Proxy Cache

Setup backend server (Node.js/Python)
Configure Nginx proxy cache
Generate traffic và monitor cache hits/misses
Check cache files in /var/cache/nginx

Bài tập 3: FastCGI Cache cho WordPress

Install WordPress
Configure FastCGI cache
Test cache bypass cho:
- Logged-in users
- Admin pages
- POST requests
Measure performance improvement

Bài tập 4: Custom Cache Keys

Setup cache với custom key (include device type)
Test từ mobile và desktop
Verify different cached versions

Bài tập 5: Cache Purging

Setup proxy cache
Create purge endpoint
Test cache purge:
- Manual purge script
- API endpoint
Verify cache cleared

Bài tập 6: Cache Performance Testing

Setup với và không có cache
Use Apache Bench để benchmark:

# Without cache ab -n 1000 -c 10 http://example.com/ With cache

ab -n 1000 -c 10 http://example.com/

Compare results

7. Troubleshooting

7.1. Cache Not Working

Problem: X-Cache-Status always shows MISS

Diagnosis:

# Check cache directory permissions ls -la /var/cache/nginx/ Check cache config sudo nginx -T | grep cache Check if cache zone defined sudo nginx -T | grep keys_zone Monitor cache files being created

watch -n 1 'ls -lh /var/cache/nginx/proxy/'

Solutions:

# Ensure proper permissions
sudo chown -R nginx:nginx /var/cache/nginx/
sudo chmod -R 755 /var/cache/nginx/
Verify cache zone
http {
proxy_cache_path /var/cache/nginx/proxy
levels=1:2
keys_zone=my_cache:10m;
server {
    location / {
        proxy_pass http://backend;
        proxy_cache my_cache;  # Must match keys_zone name
        proxy_cache_valid 200 10m;
    }
}

}

7.2. Cache Taking Too Much Disk Space

Problem: /var/cache/nginx fills up disk

Diagnosis:

# Check cache size
du -sh /var/cache/nginx/*
Find largest cache files
find /var/cache/nginx -type f -exec du -h {} + | sort -rh | head -20

Solutions:

# Set max_size
proxy_cache_path /var/cache/nginx/proxy
levels=1:2
keys_zone=my_cache:10m
max_size=1g          # Limit to 1GB
inactive=60m;         # Purge inactive files
Or use tmpfs (RAM disk)
Add to /etc/fstab:
tmpfs /var/cache/nginx tmpfs defaults,size=512M 0 0

7.3. Stale Content Being Served

Problem: Old content được serve dù đã update

Solutions:

# Clear cache manually sudo rm -rf /var/cache/nginx/proxy/* sudo systemctl reload nginx Or implement cache versioning location / { proxy_pass http://backend; proxy_cache my_cache; # Add version to cache key proxy_cache_key "$scheme$host$request_uri$arg_v"; } Usage: http://example.com/page?v=2

7.4. Cache Stampede

Problem: Nhiều requests cùng lúc khi cache expires

Solutions:

location / {
proxy_pass http://backend;
proxy_cache my_cache;
# Enable cache locking
proxy_cache_lock on;
proxy_cache_lock_timeout 5s;
proxy_cache_lock_age 5s;

# Use stale while updating
proxy_cache_use_stale updating;

}

7.5. Different Content for Same URL

Problem: User A sees User B's content

Solutions:

# Include user identifier in cache key
location / {
proxy_pass http://backend;
proxy_cache my_cache;
# Different cache per user
proxy_cache_key "$scheme$host$request_uri$cookie_user_id";

# Or bypass cache for authenticated users
set $skip_cache 0;
if ($http_cookie ~* "logged_in") {
    set $skip_cache 1;
}
proxy_cache_bypass $skip_cache;

}

8. Best Practices

8.1. Cache Strategy

# Tiered caching strategy
http {
# Hot content - short TTL, small size
proxy_cache_path /dev/shm/nginx/hot
keys_zone=hot:10m
max_size=100m
inactive=5m;
# Warm content - medium TTL, medium size
proxy_cache_path /var/cache/nginx/warm
                 keys_zone=warm:50m
                 max_size=5g
                 inactive=1h;

# Cold content - long TTL, large size
proxy_cache_path /mnt/cache/nginx/cold
                 keys_zone=cold:100m
                 max_size=50g
                 inactive=7d;

server {
    # Frequently changing content
    location /api/live/ {
        proxy_cache hot;
        proxy_cache_valid 1m;
    }
    
    # Normal content
    location / {
        proxy_cache warm;
        proxy_cache_valid 10m;
    }
    
    # Static assets
    location /static/ {
        proxy_cache cold;
        proxy_cache_valid 1y;
    }
}

}

8.2. Monitoring

# Detailed cache logging log_format cache_detail '$remote_addr - [$time_local] ' '"$request" $status $body_bytes_sent ' '"$http_referer" "$http_user_agent" ' 'cache:$upstream_cache_status ' 'rt:$request_time ' 'urt:$upstream_response_time ' 'cache_key:"$scheme$host$request_uri"'; server { access_log /var/log/nginx/cache.log cache_detail; location / { proxy_pass http://backend; proxy_cache my_cache; add_header X-Cache-Status $upstream_cache_status always; add_header X-Cache-Date $upstream_http_date; }

}

Cache statistics script:

#!/bin/bash
cache_stats.sh
LOG_FILE="/var/log/nginx/cache.log"
echo "Cache Statistics"
echo "================"
echo "Total requests: $(wc -l < $LOG_FILE)"
echo -e "\nCache status distribution:"
awk '{print $NF}' $LOG_FILE | grep "cache:" | cut -d: -f2 | sort | uniq -c | sort -rn
echo -e "\nHit rate:"
TOTAL=$(grep "cache:" $LOG_FILE | wc -l)
HITS=$(grep "cache:HIT" $LOG_FILE | wc -l)
MISS=$(grep "cache:MISS" $LOG_FILE | wc -l)
if [ $TOTAL -gt 0 ]; then
HIT_RATE=$(echo "scale=2; ($HITS * 100) / $TOTAL" | bc)
echo "Hit rate: ${HIT_RATE}%"
echo "Hits: $HITS"
echo "Misses: $MISS"
fi

8.3. Security

# Prevent cache poisoning
server {
location / {
proxy_pass http://backend;
proxy_cache my_cache;
    # Không cache responses với Set-Cookie
    proxy_ignore_headers Set-Cookie;
    proxy_hide_header Set-Cookie;
    
    # Normalize cache key (remove tracking params)
    if ($args ~* ^(.*)&amp;?(utm_[^&amp;]+)(.*)$) {
        set $args $1$3;
    }
    
    proxy_cache_key "$scheme$host$request_uri$args";
}

}

8.4. Performance

# Optimize cache performance
http {
proxy_cache_path /var/cache/nginx
levels=1:2              # Distribute files
keys_zone=cache:100m
max_size=10g
inactive=60m
use_temp_path=off       # Write directly to cache
loader_threshold=300    # Load cache metadata gradually
loader_files=200
loader_sleeps=50ms;
server {
    location / {
        proxy_pass http://backend;
        proxy_cache cache;
        
        # Buffer settings
        proxy_buffering on;
        proxy_buffer_size 16k;
        proxy_buffers 16 16k;
        
        # Cache locking
        proxy_cache_lock on;
        proxy_cache_lock_timeout 5s;
        
        # Background update
        proxy_cache_background_update on;
        proxy_cache_use_stale updating;
    }
}

}

Tổng kết

Trong bài này, bạn đã học:

✅ Browser caching với expires và Cache-Control headers
✅ Proxy caching cho static và dynamic content
✅ FastCGI caching cho PHP applications
✅ Cache keys, zones và custom strategies
✅ Cache purging và bypass techniques
✅ Performance optimization và best practices

Bài tiếp theo: Chúng ta sẽ tìm hiểu về SSL/TLS và HTTPS - cách setup SSL certificates, HTTP to HTTPS redirect, SSL protocols, HSTS và HTTP/2 configuration.

Bài 6: NGINX CACHING

TAGS

1. Browser Caching với Expires và Cache-Control Headers

1.1. Expires Header

1.2. Cache-Control Header

private: Chỉ browser cache, không cache ở proxies

no-cache: Phải revalidate trước khi dùng cache

no-store: Không cache gì cả

max-age: Cache duration (seconds)

s-maxage: Max-age cho shared caches (CDN, proxies)

must-revalidate: Phải revalidate khi stale

immutable: Content không bao giờ thay đổi

no-transform: Không cho phép transform content

1.3. Conditional Caching

1.4. ETag và Last-Modified

2. Proxy Caching Cơ bản

2.1. Cấu hình Proxy Cache Zone

2.2. Cache Status Values

2.3. Cache Key

Example:

http://example.com/page?id=1

Key: httpexample.com/page?id=1

2.4. Cache Methods và Conditions

Serve stale cache khi:

- error: Lỗi kết nối đến backend

- timeout: Backend timeout

- updating: Cache đang được update (tránh stampede)

- http_500/502/503/504: Backend trả về error codes

2.5. Complete Proxy Cache Example

3. FastCGI Caching

3.1. FastCGI Cache Configuration

3.2. WordPress với FastCGI Cache

3.3. Drupal với FastCGI Cache

3.4. Custom PHP Application với Cache

4. Cache Keys và Cache Zones

4.1. Cache Zones Configuration

4.2. Advanced Cache Keys

4.3. Cache Hierarchy

5. Cache Purging và Bypass

5.1. Cache Bypass

Usage:

Normal: http://example.com/page

Bypass: http://example.com/page?nocache=1

Refresh: http://example.com/page?refresh=1

5.2. Cache Purging (Nginx Plus / Third-party module)

Usage:

curl -X PURGE http://example.com/page

Ubuntu/Debian

CentOS - compile from source

Usage:

curl http://example.com/purge/page-to-clear

purge_cache.sh - Manual cache purge script

Purge all cache

Purge specific URL

Purge by pattern

cache_warmup.sh - Warm up cache

5.3. Selective Cache Invalidation

Usage:

curl "http://example.com/api/cache/invalidate?pattern=/products/*"

6. Bài tập Thực hành

Bài tập 1: Browser Caching

Bài tập 2: Proxy Cache

Bài tập 3: FastCGI Cache cho WordPress

Bài tập 4: Custom Cache Keys

Bài tập 5: Cache Purging

Bài tập 6: Cache Performance Testing

With cache

7. Troubleshooting

7.1. Cache Not Working

Check cache config

Check if cache zone defined

Monitor cache files being created

Verify cache zone

7.2. Cache Taking Too Much Disk Space

Find largest cache files

Or use tmpfs (RAM disk)

Add to /etc/fstab:

tmpfs /var/cache/nginx tmpfs defaults,size=512M 0 0

7.3. Stale Content Being Served

Or implement cache versioning