Nginx缓存解决方案:SRCache
前些天帮别人优化PHP程序,搞得灰头土脸,最后黔驴技穷开启了FastCGI Cache,算是勉强应付过去了吧。不过FastCGI Cache不支持分布式缓存,当服务器很多的时候,冗余的浪费将非常严重,此外还有数据一致性问题,所以它只是一个粗线条的解决方案。
对此类问题而言,SRCache是一个细粒度的解决方案。其工作原理大致如下:
当问题比较简单的时候,通常SRCache和Memc模块一起搭配使用。网上能搜索到一些相关的例子,大家可以参考,这里就不赘述了。当问题比较复杂的时候,比如说缓存键的动态计算等,就不得不写一点代码了,此时Lua模块是最佳选择。
闲言碎语不多讲,表一表Nginx配置文件长啥样:
lua_shared_dict phoenix_status 100m; lua_package_path '/path/to/phoenix/include/?.lua;/path/to/phoenix/vendor/?.lua;;'; init_by_lua_file /path/to/phoenix/config.lua; server { listen 80; server_name foo.com; root /path/to/root; index index.html index.htm index.php; location / { try_files $uri $uri/ /index.php$is_args$args; } location ~ \.php$ { set $phoenix_key ""; set $phoenix_fetch_skip 1; set $phoenix_store_skip 1; rewrite_by_lua_file /path/to/phoenix/monitor.lua; srcache_fetch_skip $phoenix_fetch_skip; srcache_store_skip $phoenix_store_skip; srcache_fetch GET /phoenix/content key=$phoenix_key; srcache_store PUT /phoenix/content key=$phoenix_key; add_header X-SRCache-Fetch-Status $srcache_fetch_status; add_header X-SRCache-Store-Status $srcache_store_status; try_files $uri =404; include fastcgi.conf; fastcgi_pass 127.0.0.1:9000; fastcgi_intercept_errors on; error_page 500 502 503 504 = /phoenix/failover; } location = /phoenix/content { internal; content_by_lua_file /path/to/phoenix/content.lua; } location = /phoenix/failover { internal; rewrite_by_lua_file /path/to/phoenix/failover.lua; } }
Nginx启动后,会载入config.lua中的配置信息。请求到达后,缺省情况下,SRCache为关闭状态,在monitor.lua中,会对当前请求进行正则匹配,一旦匹配成功,那么就会计算出缓存键,并且把SRCache设置为开启状态,最后由content.lua完成读写。
看看「config.lua」文件的内容,它主要用来记录一些全局的配置信息:
phoenix = {} phoenix["memcached"] = { default = { timeout = "100", keepalive = {idle = 10000, size = 100}, }, {host = "127.0.0.1", port = "11211"}, {host = "127.0.0.1", port = "11212"}, {host = "127.0.0.1", port = "11213"}, } phoenix["rule"] = { default = { expire = 600, min_uses = 0, max_errors = 0, query = { ["debug"] = false, }, }, { regex = "^/foo/bar", query = { ["page"] = function(v) if v == "" or v == nil then return 1 end return tonumber(v) or false end, ["limit"] = true, }, }, }
看看「monitor.lua」文件的内容,它主要用来计算缓存键,并开启SRCache模块:
local status = require "status" local status = status:new(ngx.shared.phoenix_status) local request_uri_without_args = ngx.re.sub(ngx.var.request_uri, "\\?.*", "") table.unpack = table.unpack or unpack for index, rule in ipairs(phoenix["rule"]) do if type(rule["regex"]) == "string" then rule["regex"] = {rule["regex"], ""} end local regex, options = table.unpack(rule["regex"]) if ngx.re.match(request_uri_without_args, regex, options) then local default = phoenix["rule"]["default"] local expire = rule["expire"] or default["expire"] local min_uses = rule["min_uses"] or default["min_uses"] local max_errors = rule["max_errors"] or default["max_errors"] local key = { ngx.var.request_method, " ", ngx.var.scheme, "://", ngx.var.host, request_uri_without_args, } rule["query"] = rule["query"] or {} if default["query"] then for key, value in pairs(default["query"]) do if not rule["query"][key] then rule["query"][key] = value end end end local query = {} local args = ngx.req.get_uri_args() for name, value in pairs(rule["query"]) do if type(value) == "function" then value = value(args[name]) end if value == true then value = args[name] end if value then query[name] = value elseif args[name] then return end end query = ngx.encode_args(query) if query ~= "" then key[#key + 1] = "?" key[#key + 1] = query end key = table.concat(key) key = ngx.md5(key) ngx.var.phoenix_key = key local now = ngx.time() if ngx.var.arg_phoenix == true then ngx.var.phoenix_fetch_skip = 0 else for i = 0, 1 do local errors = status:get_errors(index, now - i * 60) if errors >= max_errors then ngx.var.phoenix_fetch_skip = 0 break end end end local uses = status:incr_uses(key, 1) if uses >= min_uses then local timestamp = status:get_timestamp(key) if now - timestamp >= expire then ngx.var.phoenix_store_skip = 0 end end break end end
看看「content.lua」文件的内容,它主要通过Resty库来读写Memcached:
local memcached = require "resty.memcached" local status = require "status" local status = status:new(ngx.shared.phoenix_status) local key = ngx.var.arg_key local index = ngx.crc32_long(key) % #phoenix["memcached"] + 1 local config = phoenix["memcached"][index] local default = phoenix["memcached"]["default"] local host = config["host"] or default["host"] local port = config["port"] or default["port"] local timeout = config["timeout"] or default["timeout"] local keepalive = config["keepalive"] or default["keepalive"] local memc, err = memcached:new() if not memc then ngx.log(ngx.ERR, err) ngx.exit(ngx.HTTP_SERVICE_UNAVAILABLE) end if timeout then memc:set_timeout(timeout) end local ok, err = memc:connect(host, port) if not ok then ngx.log(ngx.ERR, err) ngx.exit(ngx.HTTP_SERVICE_UNAVAILABLE) end local method = ngx.req.get_method() if method == "GET" then local res, flags, err = memc:get(key) if err then ngx.log(ngx.ERR, err) ngx.exit(ngx.HTTP_SERVICE_UNAVAILABLE) end if res == nil and flags == nil and err == nil then ngx.exit(ngx.HTTP_NOT_FOUND) end ngx.print(res) elseif method == "PUT" then local value = ngx.req.get_body_data() local expire = ngx.var.arg_expire or 86400 local ok, err = memc:set(key, value, expire) if not ok then ngx.log(ngx.ERR, err) ngx.exit(ngx.HTTP_SERVICE_UNAVAILABLE) end status:set_timestamp(key) else ngx.exit(ngx.HTTP_NOT_ALLOWED) end if type(keepalive) == "table" then if keepalive["idle"] and keepalive["size"] then memc:set_keepalive(keepalive["idle"], keepalive["size"]) end end
看看「failover.lua」文件的内容,它是为了在出错时激活容灾模式:
ngx.req.set_uri_args(ngx.var.args .. "&phoenix") ngx.req.set_uri(ngx.var.uri, true)
此外,还有一个「status.lua」文件:
local status = {} local get_timestamp_key = function(key) key = { "phoenix", "status", "timestamp", key, } return table.concat(key, ":") end local get_uses_key = function(key, timestamp) key = { "phoenix", "status", "uses", key, os.date("%Y%m%d%H%M", timestamp), } return table.concat(key, ":") end local get_errors_key = function(key, timestamp) key = { "phoenix", "status", "errors", key, os.date("%Y%m%d%H%M", timestamp), } return table.concat(key, ":") end local get = function(shared, key) return shared:get(key) end local set = function(shared, key, value, expire) return shared:set(key, value, expire or 86400) end local incr = function(shared, key, value, expire) value = value or 1 local counter = shared:incr(key, value) if not counter then shared:add(key, 0, expire or 86400) counter = shared:incr(key, value) end return counter end function status:new(shared) return setmetatable({shared = shared}, {__index = self}) end function status:get_timestamp(key) return get(self.shared, get_timestamp_key(key)) or 0 end function status:set_timestamp(key, value, expire) key = get_timestamp_key(key) value = value or ngx.time() return set(self.shared, key, value, expire) end function status:get_uses(key, timestamp) timestamp = timestamp or ngx.time() key = get_uses_key(key, timestamp) return get(self.shared, key) or 0 end function status:incr_uses(key, value, expire) key = get_uses_key(key, ngx.time()) value = value or 1 return incr(self.shared, key, value, expire) end function status:get_errors(key, timestamp) timestamp = timestamp or ngx.time() key = get_errors_key(key, timestamp) return get(self.shared, key) or 0 end function status:incr_errors(key, value, expire) key = get_errors_key(key, ngx.time()) value = value or 1 return incr(self.shared, key, value, expire) end return status
最后一个问题:如何判断缓存是否生效了?试试下面的命令:
shell> curl -v "http://foo.com/test?x=123&y=abc" < X-SRCache-Fetch-Status: HIT < X-SRCache-Store-Status: BYPASS
目前我主要用srcache来缓存一些接口的json结果集,这些接口同时也支持jsonp,也就是客户端传递一个callback参数之类的,大家应该明白,此时如果不加区分的都缓存,那么有callback的和没有callback的调用结果就都要保存起来了,内存占用直接翻番,可实际上它们的内容大同小异,所以在实际应用时,我们应该仅仅缓存没有callback的数据,而对于有callback的请求,可以用xss-nginx-module来搞定。
关于激活SRCache前后的性能对比,视环境的不同会有所差异,不过绝对是数量级的提升,更重要的是这一切对业务层完全透明,别愣着了,快试试吧!
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- 作者:老王 来源: 火丁笔记
- 标签: Nginx SRCache 缓存
- 发布时间:2014-12-04 13:31:54
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