What is the Varnish cache server? What is the working mechanism? How to build Varnish?

If you clear the cache on the IP allowed by varnish (192.168.171.134 host), you will see the following successful message:

Attach:

The above complete uncommented configuration file is as follows:

Vcl 4.0 backend web1 import directors;import std;probe backend_healthcheck {.url = "/"; .interval = 5spoli.timeout = 1spoli.window = 5; .threshold = 3;} backend web1 {.host = "192.168.171.134"; .port = "80"; .probe = backend_healthcheck;} backend web2 {.url = "192.168.171.132"; .port = "80"; .port = backend_healthcheck } acl purgers {"127.0.0.1"; "localhost"; "192.168.171.0 web2 24";! "192.168.171.132";} sub vcl_init {new web_cluster=directors.round_robin (); web_cluster.add_backend (web1); web_cluster.add_backend (web2) } sub vcl_recv {set req.backend_hint = web_cluster.backend (); if (req.method = = "PURGE") {if (! client.ip ~ purgers) {return (synth (405, "Not Allowed."));} return (purge) } if (req.method! = "GET" & & req.method! = "HEAD" & & req.method! = "PUT" & & req.method! = "POST" & & req.method! = "TRACE" & & req.method! = "OPTIONS" & & req.method! = "PATCH" & & req.method! = "DELETE") { Return (pipe) } if (req.method! = "GET" & & req.method! = "HEAD") {return (pass);} if (req.url ~ "\. (php | asp | aspx | do | ashx | shtml) ($|\?) {return (pass);} if (req.http.Authorization) {return (pass) } if (req.http.Accept-Encoding) {if (req.url ~ "\. (bmp | png | gif | jpg | jpeg | ico | gz | tgz | bz2 | tbz | zip | rar | mp3 | mp4 | ogg | swf | flv) $") {unset req.http.Accept-Encoding;} elseif (req.http.Accept-Encoding ~ "gzip") {set req.http.Accept-Encoding = "gzip" } elseif (req.http.Accept-Encoding ~ "deflate") {set req.http.Accept-Encoding = "deflate";} else {unset req.http.Accept-Encoding;}} if (req.url ~ "\. (css | js | html | htm | bmp | png | gif | jpeg | ico | gz | tgz | bz2 | tbz | zip | rar | mp3 | mp4 | ogg | swf | flv) ($|\)) {unset req.http.cookie; return (hash) } 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;}} return (hash);} sub vcl_hash {hash_data (req.url) If (req.http.host) {hash_data (req.http.host);} else {hash_data (server.ip);} return (lookup);} sub vcl_hit {if (req.method = = "PURGE") {return (synth (200, "Purged.")) } return (deliver);} sub vcl_miss {if (req.method = = "PURGE") {return (synth (404, "Purged."));} return (fetch);} sub vcl_deliver {if (obj.hits > 0) {set resp.http.CXK = "HIT-from-varnish" Set resp.http.X-Cache-Hits = obj.hits;} else {set resp.http.X-Cache = "MISS";} unset resp.http.X-Powered-By; unset resp.http.Server; unset resp.http.X-Drupal-Cache; unset resp.http.Via; unset resp.http.Link; unset resp.http.X-Varnish Set resp.http.xx_restarts_count = req.restarts; set resp.http.xx_Age = resp.http.Age; # set resp.http.hit_count = obj.hits; # unset resp.http.Age; return (deliver);} sub vcl_pass {return (fetch);} sub vcl_backend_response {set beresp.grace = 5m If (beresp.status = = 499 | | beresp.status = = 404 | | beresp.status = = 502) {set beresp.uncacheable = true;} if (bereq.url ~ "\. (php | jsp) (\? | $)") {set beresp.uncacheable = true } else {if (bereq.url ~ "\. (css | js | html | htm | bmp | png | gif | jpg | jpeg | ico) ($|\?) {set beresp.ttl = 15m; unset beresp.http.Set-Cookie;} elseif (bereq.url ~"\. (gz | tgz | bz2 | tbz | zip | rar | mp3 | mp4 | ogg | swf | flv) ($|\?) {set beresp.ttl = 30m Unset beresp.http.Set-Cookie;} else {set beresp.ttl = 10m; unset beresp.http.Set-Cookie;}} return (deliver);} sub vcl_purge {return (synth (200m, "success")) } sub vcl_backend_error {if (beresp.status = = 500 | | beresp.status = = 501 | | beresp.status = = 502 | | beresp.status = = 503 | | beresp.status = = 504) {return (retry);}} sub vcl_fini {return (ok) } if you want to implement the caching function of varnish, you can do it through the following basic definitions (the following are in the example.vcl file): vcl 4.0 politics import directors;probe backend_healthcheck {.url = "/"; .timeout = 1s; .interval = 5s; .window = 5; .threshold = 3;} backend web1 {.host = "192.168.171.134" .port = "80"; .probe = backend_healthcheck;} backend web2 {.host = "192.168.171.132"; .port = "80"; .probe = backend_healthcheck;} sub vcl_init {new web_cluster = directors.round_robin (); web_cluster.add_backend (web1); web_cluster.add_backend (web2) } sub vcl_recv {set req.backend_hint = web_cluster.backend ();}