缓存
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缓存之所以能够生效是程序的运行具有局部性特征:
- 时间局部性:一个数据被访问过之后,可能很快会被再次访问到;
- 空间局部性:一个数据被访问时,其周边的数据也有可能被访问到
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缓存的是热区数据
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时效性:
- 缓存空间耗尽:LRU,最近最少使用;
- 过期:缓存清理
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时效性:
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缓存命中率:hit/(hit+miss)
- 页面命中率:基于页面数量进行衡量
- 字节命中率:基于页面的体积进行衡量
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缓存的数据类型
- 私有数据:private,private cache;
- 公共数据:public, public or private cache;
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Cache-related Headers Fields
The most important caching header fields are: Expires:过期时间; Expires:Thu, 22 Oct 2026 06:34:30 GMT Cache-Control:max-age= Etag If-None-Match Last-Modified If-Modified-Since Vary Age
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缓存有效性判断机制:
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过期时间:Expires
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HTTP/1.0
Expires:过期时间 -
HTTP/1.1
Cache-Control: maxage= 控制公共和私有缓存
Cache-Control: s-maxage= 控制公共缓存
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HTTP/1.0
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条件式请求:
- Last-Modified/If-Modified-Since:基于文件的修改时间戳来判别;
- Etag/If-None-Match:基于文件的校验码来判别;
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示例:
Expires:Thu, 13 Aug 2026 02:05:12 GMT Cache-Control:max-age=315360000 ETag:"1ec5-502264e2ae4c0" Last-Modified:Wed, 03 Sep 2014 10:00:27 GMT
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缓存层级:
- 私有缓存:用户代理附带的本地缓存机制;
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公共缓存:反向代理服务器的缓存功能;
User-Agent <–> private cache <–> public cache <–> public cache 2 <–> Original Server
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请求报文用于通知缓存服务如何使用缓存响应请求:
cache-request-directive = "no-cache", | "no-store" | "max-age" "=" delta-seconds | "max-stale" [ "=" delta-seconds ] | "min-fresh" "=" delta-seconds | "no-transform" | "only-if-cached" | cache-extension
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响应报文用于通知缓存服务器如何存储上级服务器响应的内容:
cache-response-directive = "public" | "private" [ "=" <"> 1#field-name <"> ] ,仅私有缓存可以响应 | "no-cache" [ "=" <"> 1#field-name <"> ],可缓存,但响应给客户端之前需要revalidation,即必须发出条件式请求进行缓存有效性验正; | "no-store" ,不允许存储响应内容于缓存中; | "no-transform" | "must-revalidate" | "proxy-revalidate" | "max-age" "=" delta-seconds | "s-maxage" "=" delta-seconds | cache-extension
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开源解决方案:
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squid
varnish
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squid
varnish
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varnish的配置:
- 定义进程配置
- 缓存系统的配置
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程序架构:
- Manager进程
- Cacher进程,包含多种类型的线程:accept, worker, expiry, …
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shared memory log:
- 统计数据:计数器;
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日志区域:日志记录;
varnishlog, varnishncsa, varnishstat…
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配置接口:VCL:Varnish Configuration Language,
vcl complier –> c complier –> shared object
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varnish的程序环境:
- /etc/varnish/varnish.params: 配置varnish服务进程的工作特性,例如监听的地址和端口,缓存机制;
- /etc/varnish/default.vcl:配置各Child/Cache线程的缓存策略;
- 主程序:/usr/sbin/varnishd
- CLI interface:/usr/bin/varnishadm
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Shared Memory Log交互工具:
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/usr/bin/varnishhist
/usr/bin/varnishlog
/usr/bin/varnishncsa
/usr/bin/varnishstat
/usr/bin/varnishtop
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/usr/bin/varnishhist
- 测试工具程序:/usr/bin/varnishtest
- VCL配置文件重载程序:/usr/sbin/varnish_reload_vcl
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Systemd Unit File:
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varnish服务:
/usr/lib/systemd/system/varnish.service -
日志持久的服务:
/usr/lib/systemd/system/varnishlog.service
/usr/lib/systemd/system/varnishncsa.service
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varnish服务:
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varnish的缓存存储机制( Storage Types):
-s [name=]type[,options]· malloc[,size] 内存存储,[,size]用于定义空间大小;重启后所有缓存项失效; · file[,path[,size[,granularity]]] 磁盘文件存储,黑盒;重启后所有缓存项失效; · persistent,path,size 文件存储,黑盒;重启后所有缓存项有效;实验;
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varnish程序的选项:
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程序选项:/etc/varnish/varnish.params文件
-a address[:port][,address[:port][…],默认为6081端口;
-T address[:port],默认为6082端口;
-s [name=]type[,options],定义缓存存储机制;
-u user
-g group
-f config:VCL配置文件;
-F:运行于前台;
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运行时参数:/etc/varnish/varnish.params文件, DEAMON_OPTS
DAEMON_OPTS=”-p thread_pool_min=5 -p thread_pool_max=500 -p thread_pool_timeout=300″-p param=value:设定运行参数及其值; 可重复使用多次;
-r param[,param…]: 设定指定的参数为只读状态;
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程序选项:/etc/varnish/varnish.params文件
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重载vcl配置文件:
~ ]# varnish_reload_vcl -
varnish的命令行:varnishadm
~]# varnishadm -S /etc/varnish/secret -T [ADDRESS:]PORT help [<command>] ping [<timestamp>] auth <response> quit banner status start stop vcl.load <configname> <filename> vcl.inline <configname> <quoted_VCLstring> vcl.use <configname> vcl.discard <configname> vcl.list param.show [-l] [<param>] param.set <param> <value> panic.show panic.clear storage.list vcl.show [-v] <configname> backend.list [<backend_expression>] backend.set_health <backend_expression> <state> ban <field> <operator> <arg> [&& <field> <oper> <arg>]... ban.list
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配置文件相关:
vcl.list :列出配置文件的版本 vcl.load:装载,加载并编译; vcl.use:激活;切换使用配置文件 vcl.discard:删除; vcl.show [-v] <configname>:查看指定的配置文件的详细信息;
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运行时参数:
param.show -l:显示内部可调的参数所有列表; param.show <PARAM> param.set <PARAM> <VALUE> 设置参数
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缓存存储:
storage.list:存储类型
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后端服务器:
backend.list :列出后端主机 backend.set_health <backend_expression> <state> #指定后端主机是健康还是不健康的
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配置文件相关:
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VCL
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”域“专有类型的配置语言;
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state engine:状态引擎;
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VCL有多个状态引擎,状态之间存在相关性,但状态引擎彼此间互相隔离;每个状态引擎可使用return(x)指明关联至哪个下一级引擎;每个状态引擎对应于vcl文件中的一个配置段,即为subroutine
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Client Side
vcl_recv, vcl_pass, vcl_hit, vcl_miss, vcl_pipe, vcl_purge, vcl_synth, vcl_deliver vcl_recv: hash:vcl_hash pass: vcl_pass pipe: vcl_pipe synth: vcl_synth purge: vcl_hash --> vcl_purge vcl_hash: lookup: hit: vcl_hit miss: vcl_miss pass, hit_for_pass: vcl_pass purge: vcl_purge
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Backend Side:
vcl_backend_fetch, vcl_backend_response, vcl_backend_error
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两个特殊的引擎:Housekeeping
vcl_init:在处理任何请求之前要执行的vcl代码:主要用于初始化VMODs; vcl_fini:所有的请求都已经结束,在vcl配置被丢弃时调用;主要用于清理VMODs;
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vcl_recv的默认配置:
sub vcl_recv { if (req.method == "PRI") { /* We do not support SPDY or HTTP/2.0 */ return (synth(405)); } if (req.method != "GET" && req.method != "HEAD" && req.method != "PUT" && req.method != "POST" && req.method != "TRACE" && req.method != "OPTIONS" && req.method != "DELETE") { /* Non-RFC2616 or CONNECT which is weird. */ return (pipe); } if (req.method != "GET" && req.method != "HEAD") { /* We only deal with GET and HEAD by default */ return (pass); } if (req.http.Authorization || req.http.Cookie) { /* Not cacheable by default */ return (pass); } return (hash); } }
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vcl的语法格式:
(1) VCL files start with vcl 4.0; (2) //, # and /* foo */ for comments; (3) Subroutines are declared with the sub keyword; 例如sub vcl_recv { ...}; (4) No loops, state-limited variables(受限于引擎的内建变量); (5) Terminating statements with a keyword for next action as argument of the return() function, i.e.: return(action);用于实现状态引擎转换; (6) Domain-specific;
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The VCL Finite State Machine
(1) Each request is processed separately; (2) Each request is independent from others at any given time; (3) States are related, but isolated; (4) return(action); exits one state and instructs Varnish to proceed to the next state; (5) Built-in VCL code is always present and appended below your own VCL;
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三类主要语法:
sub subroutine { ... }
if CONDITION { ... } else { ... }
return(), hash_data()
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VCL Built-in Functions and Keywords
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内建函数:
- hash_data():指明哈希计算的数据;减少差异,以提升命中率;
- regsub(str,regex,sub):把str中被regex第一次匹配到字符串替换为sub;主要用于URL Rewrite
- regsuball(str,regex,sub):把str中被regex每一次匹配到字符串均替换为sub;
- return()
- ban(expression)
- ban_url(regex):Bans所有的其URL可以被此处的regex匹配到的缓存对象;
- synth(status,”STRING”):purge操作;
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Keywords:
- call subroutine, return(action),new,set,unset
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操作符:
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==, !=, ~, >, >=, <, <=
逻辑操作符:&&, ||, !
变量赋值:=
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==, !=, ~, >, >=, <, <=
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标志位:
- (?i):模式匹配时不区分字符大小写
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举例:
obj.hits是内建变量,用于保存某缓存项的从缓存中命中的次数;发送响应报文的过程中,在sub vcl_deliver中定义;if (obj.hits>0) { set resp.http.X-Cache = "HIT via " + server.ip; } else { set resp.http.X-Cache = "MISS via " + server.ip; }
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内建函数:
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变量类型:
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内建变量:
req.*:request,表示由客户端发来的请求报文相关; req.http.* req.http.User-Agent, req.http.Referer, ... bereq.*:由varnish发往BE主机的httpd请求相关; bereq.http.* beresp.*:由BE主机响应给varnish的响应报文相关; beresp.http.* resp.*:由varnish响应给client相关; resp.http.* obj.*:存储在缓存空间中的缓存对象的属性;只读;
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常用变量:
bereq.*, req.*: bereq.http.HEADERS bereq.request:请求方法; bereq.url:请求的url; bereq.proto:请求的协议版本; bereq.backend:指明要调用的后端主机; req.http.Cookie:客户端的请求报文中Cookie首部的值; req.http.User-Agent ~ "chrome" beresp.*, resp.*: beresp.http.HEADERS beresp.status:响应的状态码; reresp.proto:协议版本; beresp.backend.name:BE主机的主机名; beresp.ttl:BE主机响应的内容的余下的可缓存时长; obj.* obj.hits:此对象从缓存中命中的次数; obj.ttl:对象的ttl值 server.* server.ip server.hostname client.* client.ip
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用户自定义:
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set
unset
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set
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示例1:强制对某类资源的请求不检查缓存:
vcl_recv { if (req.url ~ "(?i)^/(login|admin)") { return(pass); } }
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示例2:对于特定类型的资源,例如公开的图片等,取消其私有标识,并强行设定其可以由varnish缓存的时长; 定义在vcl_backend_response中;
if (beresp.http.cache-control !~ "s-maxage") { if (bereq.url ~ "(?i)\.(jpg|jpeg|png|gif|css|js)$") { unset beresp.http.Set-Cookie; set beresp.ttl = 3600s; } }
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示例3:将客户端的IP地址传递到后端主机,定义在vcl_recv中;
if (req.restarts == 0) { if (req.http.X-Forwarded-For) { set req.http.X-Forwarded-For = req.http.X-Forwarded-For + "," + client.ip; } else { set req.http.X-Forwarded-For = client.ip; } } 当只有一个变量 变量为字符串:非空为真,空则为假; 变量为数值型:非0为真,0则为假
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缓存对象的修剪:purge, ban
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purge
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能执行purge操作
sub vcl_purge { return (synth(200,"Purged")); }
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何时执行purge操作
sub vcl_recv { if (req.method == "PURGE") { return(purge); } ... }
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添加此类请求的访问控制法则:
acl purgers { "127.0.0.0"/8; "192.168.10.0"/24; } sub vcl_recv { if (req.method == "PURGE") { if (!client.ip ~ purgers) { return(synth(405,"Purging not allowed for " + client.ip)); } return(purge); } ... }
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能执行purge操作
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Banning:
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varnishadm:
ban <field> <operator> <arg> 示例: ban req.url ~ ^/javascripts
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在配置文件中定义,使用ban()函数;
示例: if (req.method == "BAN") { ban("req.http.host == " + req.http.host + " && req.url == " + req.url); # Throw a synthetic page so the request won't go to the backend. return(synth(200, "Ban added")); }
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如何设定使用多个后端主机:
backend default { .host = "172.16.100.6"; .port = "80"; } backend appsrv { .host = "172.16.100.7"; .port = "80"; } sub vcl_recv { if (req.url ~ "(?i)\.php$") { set req.backend_hint = appsrv; } else { set req.backend_hint = default; } ... }
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Director:
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varnish module;
使用前需要导入:import directors; -
示例:
import directors; # load the directors backend server1 { .host = .port = } backend server2 { .host = .port = } sub vcl_init { new GROUP_NAME = directors.round_robin(); GROUP_NAME.add_backend(server1); GROUP_NAME.add_backend(server2); } sub vcl_recv { # send all traffic to the bar director: set req.backend_hint = GROUP_NAME.backend(); }
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示例:
设置使用多个后端主机,采用动静分离的方式,反代至backend serverbackend imgsrv1 { .host = "192.168.10.11"; .port = "80"; } backend imgsrv2 { .host = "192.168.10.12"; .port = "80"; } backend appsrv1 { .host = "192.168.10.21"; .port = "80"; } backend appsrv2 { .host = "192.168.10.22"; .port = "80"; } sub vcl_init { new imgsrvs = directors.random(); imgsrvs.add_backend(imgsrv1,10); imgsrvs.add_backend(imgsrv2,20); new staticsrvs = directors.round_robin(); appsrvs.add_backend(appsrv1); appsrvs.add_backend(appsrv2); new appsrvs = directors.hash(); appsrvs.add_backend(appsrv1,1); appsrvs.add_backend(appsrv2,1); } sub vcl_recv { if (req.url ~ "(?i)\.(css|js)$" { set req.backend_hint = staticsrvs.backend(); } if (req.url ~ "(?i)\.(jpg|jpeg|png|gif)$" { set req.backend_hint = imgsrvs.backend(); } else { set req.backend_hint = appsrvs.backend(req.http.cookie); } }
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基于cookie的session sticky:
把来自同一用户的信息发往同一个客户端主机sub vcl_init { new h = directors.hash(); h.add_backend(one, 1); // backend 'one' with weight '1' h.add_backend(two, 1); // backend 'two' with weight '1' } sub vcl_recv { // pick a backend based on the cookie header of the client set req.backend_hint = h.backend(req.http.cookie); }
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BE Health Check:
backend BE_NAME { .host = .port = .probe = { .url= .timeout= .interval= .window= .threshold= } }
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.probe:定义健康状态检测方法;
.url:检测时要请求的URL,默认为”/”;
.request:发出的具体请求;.request = "GET /.healthtest.html HTTP/1.1" "Host: www.magedu.com" "Connection: close"
.window:基于最近的多少次检查来判断其健康状态;
.threshold:最近.window中定义的这么次检查中至有.threshhold定义的次数是成功的;
.interval:检测频度;
.timeout:超时时长;
.expected_response:期望的响应码,默认为200; -
健康状态检测的配置方式:
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probe PB_NAME { }
backend NAME = { .probe = PB_NAME; ... }
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backend NAME {.probe = {}}
backend NAME { .probe = { ... } }
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probe PB_NAME { }
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示例(1):
probe check { .url = "/.healthcheck.html"; .window = 5; .threshold = 4; .interval = 2s; .timeout = 1s; } backend default { .host = "10.1.0.68"; .port = "80"; .probe = check; }
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示例(2):
backend appsrv { .host = "10.1.0.69"; .port = "80"; .probe check { .url = "/.healthcheck.html"; .window = 5; .threshold = 4; .interval = 2s; .timeout = 1s; } }
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设置后端的主机属性:
backend BE_NAME { ... .connect_timeout = 0.5s; .first_byte_timeout = 20s; .between_bytes_timeout = 5s; .max_connections = 50; }
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varnish的运行时参数:
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线程模型:
cache-worker cache-main ban lurker acceptor: epoll/kqueue: ...
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线程相关的参数:
在线程池内部,其每一个请求由一个线程来处理; 其worker线程的最大数决定了varnish的并发响应能力;- thread_pools:Number of worker thread pools. 线程池数量最好小于或等于CPU核心数量;
- thread_pool_max:The maximum number of worker threads in each pool. 每线程池的最大线程数;
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thread_pool_min:The minimum number of worker threads in each pool. 最少线程数;额外意义为“最大空闲线程数”;
最大并发连接数=thread_pools * thread_pool_max
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thread_pool_timeout:Thread idle threshold. Threads in excess of thread_pool_min, which have been idle for at least this long, will be destroyed.空闲线程的超时时长,
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thread_pool_add_delay:Wait at least this long after creating a thread.
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thread_pool_destroy_delay:Wait this long after destroying a thread.
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Timer相关的参数:
- send_timeout:Send timeout for client connections. If the HTTP response hasn’t been transmitted in this many seconds the session is closed.
- timeout_idle:Idle timeout for client connections.
- timeout_req: Max time to receive clients request headers, measured from first non-white-space character to double CRNL.
- cli_timeout:Timeout for the childs replies to CLI requests from the mgt_param.
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设置方式:
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vcl.param
param.set
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vcl.param
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永久有效的方法:
/etc/varnish/varnish.params DEAMON_OPTS="-p PARAM1=VALUE -p PARAM2=VALUE"
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线程模型:
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varnish日志区域:
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shared memory log
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计数器
日志信息
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计数器
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varnishstat – Varnish Cache statistics
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-1
-1 -f FILED_NAME
-l:可用于-f选项指定的字段名称列表;MAIN.cache_hit MAIN.cache_miss # varnishstat -1 -f MAIN.cache_hit -f MAIN.cache_miss # varnishstat -l -f MAIN -f MEMPOOL
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varnishtop – Varnish log entry ranking
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-1 Instead of a continously updated display, print the statistics once and exit.
-i taglist,可以同时使用多个-i选项,也可以一个选项跟上多个标签;
-I <[taglist:]regex>
-x taglist:排除列表
-X <[taglist:]regex>
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-1 Instead of a continously updated display, print the statistics once and exit.
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varnishlog – Display Varnish logs
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varnishncsa – Display Varnish logs in Apache / NCSA combined log format
开启varnish的日志记录: systemctl start varnishncsa.service systemctl enable varnishncsa.service tail /var/log/varnish/varnishncsa.log
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shared memory log
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