Implement NGINX Lua scripting for advanced caching logic with OpenResty

Update system packages

Start by updating your package manager to ensure you get the latest versions.

sudo apt update && sudo apt upgrade -y

sudo dnf update -y

Install OpenResty

OpenResty provides NGINX with integrated Lua JIT support and additional modules for advanced scripting.

wget -qO - https://openresty.org/package/pubkey.gpg | sudo apt-key add -
echo "deb http://openresty.org/package/ubuntu $(lsb_release -sc) main" | sudo tee /etc/apt/sources.list.d/openresty.list
sudo apt update
sudo apt install -y openresty openresty-resty

sudo yum-config-manager --add-repo https://openresty.org/package/centos/openresty.repo
sudo dnf install -y openresty openresty-resty

Create Lua script directory

Create a dedicated directory for Lua scripts with proper ownership and permissions.

sudo mkdir -p /etc/openresty/lua
sudo chown -R nobody:nobody /etc/openresty/lua
sudo chmod 755 /etc/openresty/lua

Configure OpenResty main configuration

Set up the main OpenResty configuration with Lua support and shared memory zones for caching.

user nobody;
worker_processes auto;
worker_rlimit_nofile 65535;

events {
    worker_connections 4096;
    use epoll;
    multi_accept on;
}

http {
    include /etc/openresty/mime.types;
    default_type application/octet-stream;

    # Lua package path
    lua_package_path '/etc/openresty/lua/?.lua;;';

    # Shared memory zones for caching
    lua_shared_dict cache_dict 100m;
    lua_shared_dict cache_stats 10m;
    lua_shared_dict cache_locks 1m;

    # Initialize Lua modules
    init_by_lua_file /etc/openresty/lua/init.lua;
    init_worker_by_lua_file /etc/openresty/lua/init_worker.lua;

    # Logging
    log_format main '$remote_addr - $remote_user [$time_local] "$request" '
                    '$status $body_bytes_sent "$http_referer" '
                    '"$http_user_agent" cache_status=$cache_status '
                    'cache_key="$cache_key" ttl=$cache_ttl';

    access_log /var/log/openresty/access.log main;
    error_log /var/log/openresty/error.log warn;

    # Performance optimizations
    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    keepalive_timeout 65;
    client_max_body_size 50m;
    client_body_timeout 60;
    client_header_timeout 60;
    send_timeout 60;

    # Compression
    gzip on;
    gzip_vary on;
    gzip_proxied any;
    gzip_comp_level 6;
    gzip_types text/plain text/css text/xml text/javascript application/javascript application/xml+rss application/json;

    include /etc/openresty/conf.d/*.conf;
}

Create Lua initialization script

Initialize global variables and load required Lua modules during NGINX startup.

-- Global configuration
local _M = {}

-- Cache configuration
_M.cache_config = {
    default_ttl = 3600,  -- 1 hour
    max_ttl = 86400,     -- 24 hours
    min_ttl = 300,       -- 5 minutes
    
    -- TTL by content type
    content_ttl = {
        ["text/html"] = 1800,      -- 30 minutes
        ["application/json"] = 900, -- 15 minutes
        ["text/css"] = 7200,       -- 2 hours
        ["application/javascript"] = 7200, -- 2 hours
        ["image/"] = 86400,        -- 24 hours for images
    },
    
    -- Cache zones
    zones = {
        static = "static_cache",
        dynamic = "dynamic_cache",
        api = "api_cache"
    }
}

-- Performance settings
_M.performance = {
    max_cache_size = "500m",
    inactive = "7d",
    use_temp_path = false
}

return _M

Create worker initialization script

Set up per-worker initialization for cache statistics and background tasks.

local cache_stats = ngx.shared.cache_stats

-- Initialize cache statistics
cache_stats:set("hits", 0)
cache_stats:set("misses", 0)
cache_stats:set("invalidations", 0)
cache_stats:set("start_time", ngx.time())

-- Background cleanup timer
local function cleanup_expired_keys()
    local cache_dict = ngx.shared.cache_dict
    local keys = cache_dict:get_keys(1000)
    local cleaned = 0
    
    for _, key in ipairs(keys) do
        local value, flags = cache_dict:get(key)
        if not value then
            cache_dict:delete(key)
            cleaned = cleaned + 1
        end
    end
    
    if cleaned > 0 then
        ngx.log(ngx.INFO, "Cleaned ", cleaned, " expired cache keys")
    end
end

-- Run cleanup every 5 minutes
local ok, err = ngx.timer.every(300, cleanup_expired_keys)
if not ok then
    ngx.log(ngx.ERR, "Failed to create cleanup timer: ", err)
end

Create advanced cache module

Implement the main caching logic with dynamic key generation and intelligent TTL management.

local _M = {}

local cache_dict = ngx.shared.cache_dict
local cache_stats = ngx.shared.cache_stats
local cache_locks = ngx.shared.cache_locks

-- Generate dynamic cache key based on request context
function _M.generate_cache_key()
    local uri = ngx.var.uri
    local args = ngx.var.args or ""
    local user_type = ngx.var.http_x_user_type or "anonymous"
    local device_type = _M.detect_device_type()
    local geo_region = ngx.var.http_cf_ipcountry or "unknown"
    
    -- Custom key generation logic
    local key_parts = {
        "v2",  -- version prefix
        ngx.md5(uri .. "?" .. args),
        user_type,
        device_type,
        geo_region
    }
    
    local cache_key = table.concat(key_parts, ":")
    ngx.var.cache_key = cache_key
    return cache_key
end

-- Detect device type from user agent
function _M.detect_device_type()
    local user_agent = ngx.var.http_user_agent or ""
    
    if string.match(user_agent, "Mobile") or string.match(user_agent, "Android") then
        return "mobile"
    elseif string.match(user_agent, "Tablet") or string.match(user_agent, "iPad") then
        return "tablet"
    else
        return "desktop"
    end
end

-- Calculate intelligent TTL based on content and context
function _M.calculate_ttl(content_type, uri)
    local config = require("init")
    local base_ttl = config.cache_config.default_ttl
    
    -- TTL by content type
    for pattern, ttl in pairs(config.cache_config.content_ttl) do
        if string.match(content_type or "", pattern) then
            base_ttl = ttl
            break
        end
    end
    
    -- Adjust TTL based on URI patterns
    if string.match(uri, "/api/") then
        base_ttl = math.min(base_ttl, 900)  -- Max 15 minutes for API
    elseif string.match(uri, "/admin/") then
        base_ttl = 0  -- No caching for admin pages
    elseif string.match(uri, "\.(css|js|png|jpg|jpeg|gif|ico|svg)$") then
        base_ttl = 86400  -- 24 hours for static assets
    end
    
    -- Time-based adjustments
    local hour = tonumber(os.date("%H"))
    if hour >= 9 and hour <= 17 then
        -- Shorter TTL during business hours for dynamic content
        if not string.match(uri, "\.(css|js|png|jpg|jpeg|gif|ico|svg)$") then
            base_ttl = base_ttl * 0.5
        end
    end
    
    ngx.var.cache_ttl = base_ttl
    return base_ttl
end

-- Get cached content
function _M.get_cached_content(cache_key)
    local cached_data = cache_dict:get(cache_key)
    if cached_data then
        cache_stats:incr("hits", 1)
        ngx.var.cache_status = "HIT"
        return cached_data
    else
        cache_stats:incr("misses", 1)
        ngx.var.cache_status = "MISS"
        return nil
    end
end

-- Store content in cache with TTL
function _M.store_cached_content(cache_key, content, ttl)
    if ttl <= 0 then
        ngx.var.cache_status = "BYPASS"
        return false
    end
    
    local success, err = cache_dict:set(cache_key, content, ttl)
    if success then
        ngx.var.cache_status = "STORED"
        return true
    else
        ngx.log(ngx.ERR, "Failed to store cache: ", err)
        ngx.var.cache_status = "ERROR"
        return false
    end
end

-- Invalidate cache by pattern
function _M.invalidate_cache_pattern(pattern)
    local keys = cache_dict:get_keys(1000)
    local invalidated = 0
    
    for _, key in ipairs(keys) do
        if string.match(key, pattern) then
            cache_dict:delete(key)
            invalidated = invalidated + 1
        end
    end
    
    cache_stats:incr("invalidations", invalidated)
    return invalidated
end

-- Cache warming function
function _M.warm_cache(urls)
    for _, url in ipairs(urls) do
        local res = ngx.location.capture(url, { method = ngx.HTTP_GET })
        if res.status == 200 then
            ngx.log(ngx.INFO, "Warmed cache for: ", url)
        end
    end
end

return _M

Create cache invalidation module

Implement intelligent cache invalidation based on business logic and webhook triggers.

local _M = {}

local cache = require("cache")
local cache_dict = ngx.shared.cache_dict
local cache_stats = ngx.shared.cache_stats

-- Invalidation rules based on content updates
_M.invalidation_rules = {
    -- User profile updates
    {
        trigger = "/api/users/profile",
        method = "POST|PUT|PATCH",
        patterns = { "v2:.*:user:.*", "v2:.*profile.*" }
    },
    -- Product catalog updates
    {
        trigger = "/api/products",
        method = "POST|PUT|DELETE",
        patterns = { "v2:.*products.*", "v2:.*catalog.*" }
    },
    -- CMS content updates
    {
        trigger = "/admin/content",
        method = "POST|PUT|DELETE",
        patterns = { "v2:.*:anonymous:.*", "v2:.*content.*" }
    }
}

-- Process invalidation webhook
function _M.process_invalidation_webhook()
    ngx.req.read_body()
    local body = ngx.req.get_body_data()
    
    if not body then
        ngx.status = 400
        ngx.say('{"error": "No body provided"}')
        return
    end
    
    local cjson = require "cjson"
    local ok, data = pcall(cjson.decode, body)
    
    if not ok then
        ngx.status = 400
        ngx.say('{"error": "Invalid JSON"}')
        return
    end
    
    local invalidated = 0
    
    -- Process custom patterns
    if data.patterns then
        for _, pattern in ipairs(data.patterns) do
            invalidated = invalidated + cache.invalidate_cache_pattern(pattern)
        end
    end
    
    -- Process entity-based invalidation
    if data.entity and data.entity_id then
        local pattern = ".*:" .. data.entity .. ":" .. data.entity_id .. ".*"
        invalidated = invalidated + cache.invalidate_cache_pattern(pattern)
    end
    
    -- Process tag-based invalidation
    if data.tags then
        for _, tag in ipairs(data.tags) do
            local pattern = ".*:tag:" .. tag .. ".*"
            invalidated = invalidated + cache.invalidate_cache_pattern(pattern)
        end
    end
    
    ngx.status = 200
    ngx.say(string.format('{"invalidated": %d, "status": "success"}', invalidated))
end

-- Smart invalidation based on request
function _M.smart_invalidation()
    local method = ngx.var.request_method
    local uri = ngx.var.uri
    
    -- Only process write operations
    if method ~= "POST" and method ~= "PUT" and method ~= "PATCH" and method ~= "DELETE" then
        return
    end
    
    local invalidated = 0
    
    -- Apply invalidation rules
    for _, rule in ipairs(_M.invalidation_rules) do
        if string.match(uri, rule.trigger) and string.match(method, rule.method) then
            for _, pattern in ipairs(rule.patterns) do
                invalidated = invalidated + cache.invalidate_cache_pattern(pattern)
            end
        end
    end
    
    if invalidated > 0 then
        ngx.log(ngx.INFO, "Smart invalidation: ", invalidated, " keys for ", method, " ", uri)
    end
end

-- Time-based invalidation
function _M.schedule_time_based_invalidation()
    local hour = tonumber(os.date("%H"))
    local minute = tonumber(os.date("%M"))
    
    -- Daily cache refresh at 3 AM
    if hour == 3 and minute == 0 then
        local invalidated = cache.invalidate_cache_pattern("v2:.*:dynamic:.*")
        ngx.log(ngx.INFO, "Daily cache refresh: ", invalidated, " keys invalidated")
    end
    
    -- Hourly API cache refresh during business hours
    if hour >= 9 and hour <= 17 and minute == 0 then
        local invalidated = cache.invalidate_cache_pattern("v2:.*api.*")
        ngx.log(ngx.INFO, "Hourly API cache refresh: ", invalidated, " keys invalidated")
    end
end

return _M

Create cache statistics and monitoring module

Implement comprehensive cache monitoring and performance metrics collection.

local _M = {}

local cache_stats = ngx.shared.cache_stats
local cache_dict = ngx.shared.cache_dict

-- Get cache statistics
function _M.get_cache_stats()
    local hits = cache_stats:get("hits") or 0
    local misses = cache_stats:get("misses") or 0
    local invalidations = cache_stats:get("invalidations") or 0
    local start_time = cache_stats:get("start_time") or ngx.time()
    
    local total_requests = hits + misses
    local hit_rate = total_requests > 0 and (hits / total_requests * 100) or 0
    local uptime = ngx.time() - start_time
    
    return {
        hits = hits,
        misses = misses,
        total_requests = total_requests,
        hit_rate = string.format("%.2f%%", hit_rate),
        invalidations = invalidations,
        uptime = uptime,
        uptime_human = _M.format_uptime(uptime),
        memory_usage = _M.get_memory_usage(),
        top_keys = _M.get_top_cache_keys()
    }
end

-- Format uptime in human readable format
function _M.format_uptime(seconds)
    local days = math.floor(seconds / 86400)
    local hours = math.floor((seconds % 86400) / 3600)
    local minutes = math.floor((seconds % 3600) / 60)
    local secs = seconds % 60
    
    return string.format("%dd %02dh %02dm %02ds", days, hours, minutes, secs)
end

-- Get memory usage statistics
function _M.get_memory_usage()
    local capacity = cache_dict:capacity()
    local free_space = cache_dict:free_space()
    local used_space = capacity - free_space
    local usage_percent = (used_space / capacity) * 100
    
    return {
        capacity = capacity,
        used = used_space,
        free = free_space,
        usage_percent = string.format("%.2f%%", usage_percent)
    }
end

-- Get most frequently accessed cache keys
function _M.get_top_cache_keys(limit)
    limit = limit or 10
    local keys = cache_dict:get_keys(1000)
    local key_stats = {}
    
    -- This is a simplified version - in production you'd track access counts
    for i = 1, math.min(#keys, limit) do
        table.insert(key_stats, {
            key = keys[i],
            size = string.len(cache_dict:get(keys[i]) or "")
        })
    end
    
    return key_stats
end

-- Export stats in Prometheus format
function _M.export_prometheus_metrics()
    local stats = _M.get_cache_stats()
    
    local metrics = {
        "# HELP openresty_cache_hits_total Total number of cache hits",
        "# TYPE openresty_cache_hits_total counter",
        string.format("openresty_cache_hits_total %d", stats.hits),
        
        "# HELP openresty_cache_misses_total Total number of cache misses",
        "# TYPE openresty_cache_misses_total counter", 
        string.format("openresty_cache_misses_total %d", stats.misses),
        
        "# HELP openresty_cache_hit_rate Cache hit rate percentage",
        "# TYPE openresty_cache_hit_rate gauge",
        string.format("openresty_cache_hit_rate %s", string.gsub(stats.hit_rate, "%%", "")),
        
        "# HELP openresty_cache_memory_usage_bytes Memory usage in bytes",
        "# TYPE openresty_cache_memory_usage_bytes gauge",
        string.format("openresty_cache_memory_usage_bytes %d", stats.memory_usage.used)
    }
    
    return table.concat(metrics, "\n") .. "\n"
end

return _M

Configure virtual server with advanced caching

Create a virtual server configuration that demonstrates the advanced caching functionality.

server {
    listen 80;
    server_name example.com;
    
    # Variables for cache operations
    set $cache_key "";
    set $cache_status "";
    set $cache_ttl "";
    
    # Cache directory for file-based caching
    location / {
        # Generate cache key
        access_by_lua_block {
            local cache = require("cache")
            cache.generate_cache_key()
        }
        
        # Try to serve from Lua cache first
        content_by_lua_block {
            local cache = require("cache")
            local cache_key = ngx.var.cache_key
            
            -- Try to get from cache
            local cached_content = cache.get_cached_content(cache_key)
            if cached_content then
                ngx.print(cached_content)
                ngx.exit(200)
            else
                -- Forward to backend and cache response
                local res = ngx.location.capture("/backend" .. ngx.var.uri .. (ngx.var.args and "?" .. ngx.var.args or ""))
                
                if res.status == 200 then