Varnish is an HTTP accelerator designed for content-heavy dynamic web sites as well as heavily consumed APIs.

TYPE OF CACHES

BROWSER CACHE

CLIENT PROXY CACHE

REVERSE PROXY CACHE

HOW IT WORKS?

HOW IT WORKS?

HOW IT WORKS?

HTTP EXPIRATION

HTTP EXPIRATION

HTTP EXPIRATION

HTTP VALIDATION

HTTP VALIDATION

HTTP VALIDATION

VCL

VCL

STATE MACHINE

STATE MACHINE

STATE MACHINE

VCL_RECV

    # All unknown methods should be piped to the backend
    if (req.method != "GET" &&
        req.method != "HEAD" &&
        req.method != "PUT" &&
        req.method != "POST" &&
        req.method != "TRACE" &&
        req.method != "OPTIONS" &&
        req.method != "DELETE") {
        std.log("Unknown method " + req.method + " is piped to the backend");
        return(pipe);
    }
 
    # We only deal with GET and HEAD by default
    if (req.method != "GET" && req.method != "HEAD") {
        std.log("Method is " + req.method + " and passed to the backend directly");
        return(pass);
    }

VCL_RECV

    # This block will remove every unknown cookie except the server known cookies.
    # Known server cookies are: sid (early PHPSESSID), session_token
    if (req.http.Cookie && !req.http.X-Cookie) {
        set req.http.Cookie = ";" + req.http.Cookie;
        set req.http.Cookie = regsuball(req.http.Cookie, "; +", ";");
        set req.http.Cookie = regsuball(req.http.Cookie, ";(sid|session_token|ssid)=", "; \1=");
        set req.http.Cookie = regsuball(req.http.Cookie, ";[^ ][^;]*", "");
        set req.http.Cookie = regsuball(req.http.Cookie, "^[; ]+|[; ]+$", "");
 
        # Clean empty Cookie header
        if (req.http.Cookie == "") {
            unset req.http.Cookie;
        }
 
        # Save cookie to X-Cookie header
        set req.http.X-Cookie = req.http.Cookie;
    }
 
    # All internal subrequests that declared stateless will be made without any cookies
    if (req.url ~ "^/_internal/" && req.url ~ "stateless") {
        std.log("Request to the internal stateless block, will be made without any cookies");
        unset req.http.Cookie;
    }

VCL_RECV

    # Inform backend that we capable to process surrogates
    set req.http.Surrogate-Capability = "Varnish=ESI/1.0";
 
    # Always try to lookup, even for clients with cookies
    std.log("Trying to lookup in the cache");
    return(hash);

VCL_BACKEND_RESPONSE

    # Instruct Varnish to keep the objects in the cache beyond their TTL
    set beresp.grace = 24h;
 
    # Copy url to internal headers for lurker-friendly bans
    set beresp.http.X-Url  = bereq.url;
    set beresp.http.X-Host = bereq.http.host;
 
    # Enable processing of ESI if backend has reported that it want to be processed with ESI
    if (beresp.http.Surrogate-Control ~ "ESI/1.0") {
        unset beresp.http.Surrogate-Control;
 
        // for Varnish >= 3.0
        set beresp.do_esi = true;
    }

VCL_BACKEND_RESPONSE

    # Cache 404s and 301s for 5 minutes to prevent a possible attack on backends
    if (beresp.status == 404 || beresp.status == 301) {
        std.log("Received " + beresp.status + " code from the backend. Cache it");
        set beresp.ttl = 5m;
        return(deliver);
    }
 
    # Do not cache anything with no-cache directive
    if (beresp.http.Cache-Control ~ "no-cache") {
        set beresp.uncacheable = true;
    }

VCL_HIT

sub vcl_hit {
 
    if (obj.ttl >= 0s) {
        # A pure unadultered hit, deliver it
        return (deliver);
    }
    # Graced delivery
    if (obj.ttl + obj.grace > 0s) {
        set req.http.X-Cache-Has-Stale = true;
        return (deliver);
    }
 
    # Fetch & deliver once we get the result
    return (fetch);
}

CACHE INVALIDATION

sub vcl_recv {
    # Restrict access to the PURGE method by "purge" ACL
    if (req.method == "PURGE") {
        if (!std.ip(regsub(req.http.X-Forwarded-For, "[, ].*$", ""), client.ip) ~ purge) {
            return (synth(405, "Not allowed."));
        }
        ban("obj.http.X-Host == " + req.http.host + " 
           && obj.http.X-Url ~ " + req.http.X-Purge-Regex);
        return (synth(200, "Purged. Host: " + req.http.host + 
           " Regex:" + req.http.X-Purge-Regex));
    }
}

LIVE REFRESH

sub vcl_recv {

    # Editors can reload cache by forcing page
    if (req.http.Cache-Control ~ "no-cache" &&
        std.ip(regsub(req.http.X-Forwarded-For, "[, ].*$", ""), client.ip) ~ editors) {
        std.log("Editor from IP: " + client.ip + " requests a cache refresh");
 
        std.log("Mark request as always miss from cache");
        set req.hash_always_miss = true;
        set req.http.X-Cache-Always-Miss = true;
    }
}

THANKS!