發佈於 作者: Quanto

Nginx + Lua + memcached

整體結構

Client
↓
Nginx (OpenResty + Lua)
↓ ↘
Memcached Apache (localhost)

使用 OpenResty（Nginx + Lua 的標準發行版），不用自己安裝LUA

安裝 OpenResty（範例：Ubuntu / Debian）


sudo apt install -y curl gnupg
curl -fsSL 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

啟動：

sudo systemctl start openresty

安裝 memcached

sudo apt install -y memcached
sudo systemctl start memcached

測試：

echo stats | nc 127.0.0.1 11211

檔案結構（建議）

/usr/local/openresty/nginx/
├─ conf/nginx.conf
└─ lua/cache.lua

Nginx 設定檔（nginx.conf）

worker_processes auto;

events {
    worker_connections 4096;
}

http {
    # Lua 檔案路徑
    lua_package_path "/usr/local/openresty/nginx/lua/?.lua;;";

    # 日誌（debug 時非常重要）
    error_log logs/error.log info;

    # upstream：本機 Apache
    upstream apache_backend {
        server 127.0.0.1:8080;
        keepalive 32;
    }

    server {
        listen 80;
        server_name _;

        # === 入口 ===
        location / {
            # 所有 request 先交給 Lua
            content_by_lua_file /usr/local/openresty/nginx/lua/cache.lua;
        }

        # === 真正的後端（只有 Lua 會跳進來） ===
        location @backend {
            proxy_http_version 1.1;
            proxy_set_header Connection "";

            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;

            proxy_pass http://apache_backend;

            # ===== 把 Apache 回來的 response 存進 memcached =====
            body_filter_by_lua_block {
                -- 只在 MISS 時才寫 cache
                if not ngx.ctx.cache_key then
                    return
                end

                local chunk = ngx.arg[1]
                local eof   = ngx.arg[2]

                ngx.ctx.buffer = (ngx.ctx.buffer or "") .. (chunk or "")

                if eof then
                    local memcached = require "resty.memcached"
                    local memc = memcached:new()
                    memc:set_timeout(50)

                    -- 從 ctx 取回 key / ttl（由 cache.lua 設定）
                    local key = ngx.ctx.cache_key
                    local ttl = ngx.ctx.cache_ttl or 30

                    -- 與 cache.lua 使用同一組節點與 hash
                    local servers = {
                        { host = "10.0.0.1", port = 11211 },
                        { host = "10.0.0.2", port = 11211 },
                        { host = "10.0.0.3", port = 11211 },
                    }

                    local function pick(key)
                        local idx = (ngx.crc32_long(key) % #servers) + 1
                        return servers[idx]
                    end

                    local s = pick(key)
                    local ok, err = memc:connect(s.host, s.port)
                    if ok then
                        memc:set(key, ngx.ctx.buffer, ttl)
                        memc:set_keepalive()
                    else
                        ngx.log(ngx.ERR, "memcached set failed: ", err)
                    end
                end
            }
        }
    }
}

Lua 程式（cache.lua）

local memcached = require "resty.memcached"

-- memcached servers
local memc_servers = {
    { host = "10.0.0.1", port = 11211 },
    { host = "10.0.0.2", port = 11211 },
    { host = "10.0.0.3", port = 11211 },
}

local function pick_memc_server(key)
    local crc = ngx.crc32_long(key)
    local idx = (crc % #memc_servers) + 1
    return memc_servers[idx]
end

-- request params
local args = ngx.req.get_uri_args()
local func = args["function"]
local fun2 = args["fun2"]

-- function=a → bypass cache
if func == "a" then
    ngx.header["X-Cache"] = "BYPASS"
    return ngx.exec("@backend")
end

-- cookie
local user_cookie = ngx.var.cookie_user_id or ""

-- cache key
local raw_key =
    ngx.var.request_method .. "|" ..
    ngx.var.uri .. "|" ..
    (ngx.var.args or "") .. "|" ..
    user_cookie

local cache_key = "cache:" .. ngx.md5(raw_key)

-- TTL logic
local ttl = 30
if func == "b" and (fun2 == "BB" or fun2 == "CC") then
    ttl = 10
end

-- connect memcached
local memc = memcached:new()
memc:set_timeout(50)

local server = pick_memc_server(cache_key)
local ok, err = memc:connect(server.host, server.port)
if not ok then
    ngx.log(ngx.ERR, err)
    return ngx.exec("@backend")
end

-- get cache
local res, flags, err = memc:get(cache_key)
if res then
    ngx.header["X-Cache"] = "HIT"
    ngx.say(res)
    memc:set_keepalive()
    return
end

ngx.header["X-Cache"] = "MISS"
ngx.ctx.cache_key = cache_key
ngx.ctx.cache_ttl = ttl

ngx.exec("@backend")

Reload

/usr/local/openresty/nginx/sbin/nginx -t
/usr/local/openresty/nginx/sbin/nginx -s reload

測試

curl -i "http://server/test.php?function=b&fun2=BB"
你應該會看到：

css
複製程式碼
X-Cache: MISS
第二次：

css
複製程式碼
X-Cache: HIT

cache.lua 也可以改成有鎖的版本

local memcached = require "resty.memcached"

-- memcached servers
local memc_servers = {
    { host = "10.0.0.1", port = 11211 },
    { host = "10.0.0.2", port = 11211 },
    { host = "10.0.0.3", port = 11211 },
}

local function pick_memc_server(key)
    local crc = ngx.crc32_long(key)
    local idx = (crc % #memc_servers) + 1
    return memc_servers[idx]
end

-- request params
local args = ngx.req.get_uri_args()
local func = args["function"]
local fun2 = args["fun2"]

-- function=a → bypass cache
if func == "a" then
    ngx.header["X-Cache"] = "BYPASS"
    return ngx.exec("@backend")
end

-- cookie
local user_cookie = ngx.var.cookie_user_id or ""

-- cache key
local raw_key =
    ngx.var.request_method .. "|" ..
    ngx.var.uri .. "|" ..
    (ngx.var.args or "") .. "|" ..
    user_cookie

local cache_key = "cache:" .. ngx.md5(raw_key)

-- TTL logic
local ttl = 30
if func == "b" and (fun2 == "BB" or fun2 == "CC") then
    ttl = 10
end

-- pick memcached server
local server = pick_memc_server(cache_key)
local memc = memcached:new()
memc:set_timeout(50)
local ok, err = memc:connect(server.host, server.port)
if not ok then
    ngx.log(ngx.ERR, "memcached connect failed: ", err)
    return ngx.exec("@backend")
end

-- 1️⃣ 先查 cache
local res, flags, err = memc:get(cache_key)
if res then
    ngx.header["X-Cache"] = "HIT"
    ngx.say(res)
    memc:set_keepalive()
    return
end

-- 2️⃣ 嘗試 set lock，避免 cache stampede
local lock_key = "lock:" .. cache_key
local lock_ttl = 5  -- lock 最長存活 5 秒

local lock_set, err = memc:add(lock_key, "1", lock_ttl)
if lock_set then
    -- 成功獲得鎖 → 我去打後端
    ngx.header["X-Cache"] = "MISS|LOCKED"
    ngx.ctx.cache_key = cache_key
    ngx.ctx.cache_ttl = ttl
    return ngx.exec("@backend")
else
    -- 沒拿到鎖 → 等待 / retry
    ngx.header["X-Cache"] = "MISS|WAIT"
    local wait_time = 0
    local wait_interval = 0.05  -- 50ms
    local max_wait = 2           -- 最多等 2 秒

    while wait_time < max_wait do
        local res2, _, _ = memc:get(cache_key)
        if res2 then
            ngx.say(res2)
            memc:set_keepalive()
            return
        end
        ngx.sleep(wait_interval)
        wait_time = wait_time + wait_interval
    end

    -- 超時沒拿到 cache → 仍然打後端
    ngx.ctx.cache_key = cache_key
    ngx.ctx.cache_ttl = ttl
    return ngx.exec("@backend")
end

Nginx 可以解決的痛點

  • 非阻塞 → 不會被慢 PHP 卡死
  • cache + lock → 重複請求不打 Apache
  • rate limit → 攻擊 / 高併發被控管
  • 輕量記憶體使用 → 上萬連線仍穩定

Apache 容易卡住的原因

  • 每個 thread/process 都要維護 TCP / TLS / PHP context
  • 如果後端 PHP 執行慢：
    • 連線被占用
    • 新連線等待 → client 超時
  • 高併發時記憶體爆掉
  • Linux process scheduler 開銷大，context switch 成本高

結果：Apache 看起來「卡住」或「無法回收 thread」

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