Varnish 3 configuration

Shared caches are pretty strict when it comes to caching or not a request. This is good, otherwise it would cache requests that are not meant to be cached.

However, there is some things that can be done to improve cacheability:

1. Ignore Google Analytics cookies
2. Remove empty Cookie line
3. Normalize Accept-Encoding header
4. Allow replying with a stale response if the backend is slow

Bonus:

1. Remove some headers to reduce header size and hide some details about the server (security).
2. Add a debug header to help understand why a request is cached or not.

# default.vcl
# 
# Varnish 3
#

# Change this for your needs
backend default {
    .host = "127.0.0.1";
    .port = "8080";
}

# Authorized hosts for PURGE requests
acl purge {
  "localhost";
	"127.0.0.1";
}

# Below is a commented-out copy of the default VCL logic.  If you
# redefine any of these subroutines, the built-in logic will be
# appended to your code.
# sub vcl_recv {
#   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;
# 	}
#     }
#     if (req.request != "GET" &&
#       req.request != "HEAD" &&
#       req.request != "PUT" &&
#       req.request != "POST" &&
#       req.request != "TRACE" &&
#       req.request != "OPTIONS" &&
#       req.request != "DELETE") {
#         /* Non-RFC2616 or CONNECT which is weird. */
#         return (pipe);
#     }
#     if (req.request != "GET" && req.request != "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 (lookup);
# }

sub vcl_recv {
	# Serve objects up to 2 minutes past their expiry if the backend is slow to respond.
	set req.grace = 120s;

	# Disable Varnish on some hosts
	# if (req.http.Host ~ "dev\.example\.com$) {
	# 	return (pass); 
	# } 

	# Ignore cookies for static files
	if (req.url ~ "\.(js|css|jpe?g|png|gif|tiff|avi|mov|mp3|ogg|wmv|wma|woff|ttf|otf|svg)") {
		unset req.http.cookie;
	}

	# Disable caching when user specifically asks for it
	if (req.http.Cache-Control ~ "no-cache" || req.http.Pragma ~ "no-cache") {
		return (pass);
	}

	# From http:#serverfault.com/questions/195654/how-to-cache-websites-using-varnish-php-and-cookies
	# Remove Google Analytics Cookies
	set req.http.Cookie = regsuball(req.http.Cookie, "(^|; ) *(__)?utm[a-z0-9_]+=[^;]+;? *", "");

	# Enable purging, but only from authorized hosts
	if (req.request == "PURGE") {
		if (!client.ip ~ purge) {
			error 405 "Not allowed.";
		}
		return (lookup);
	}

	# normalize Accept-Encoding to reduce vary
	if (req.http.Accept-Encoding) {
		if (req.http.User-Agent ~ "MSIE 6") {
			unset req.http.Accept-Encoding;
		} elsif (req.http.Accept-Encoding ~ "gzip") {
			set req.http.Accept-Encoding = "gzip";
		} elsif (req.http.Accept-Encoding ~ "deflate") {
			set req.http.Accept-Encoding = "deflate";
		} else {
			unset req.http.Accept-Encoding;
		}
	}

	# Unset empty Cookie string
	if (req.http.Cookie ~ "^[\s;]*$") {
		unset req.http.Cookie;
	}
}

# sub vcl_pipe {
#     # Note that only the first request to the backend will have
#     # X-Forwarded-For set.  If you use X-Forwarded-For and want to
#     # have it set for all requests, make sure to have:
#     # set bereq.http.connection = "close";
#     # here.  It is not set by default as it might break some broken web
#     # applications, like IIS with NTLM authentication.
#     return (pipe);
# }
# 
# sub vcl_pass {
#     return (pass);
# }

sub vcl_pass {
	if (req.request == "PURGE") {
		error 502 "PURGE on a passed object";
	}
}

# 
# sub vcl_hash {
#     hash_data(req.url);
#     if (req.http.host) {
#         hash_data(req.http.host);
#     } else {
#         hash_data(server.ip);
#     }
#     return (hash);
# }

# sub vcl_hit {
#     return (deliver);
# }
# 

sub vcl_hit {
	if (req.request == "PURGE") {
		purge;
		error 200 "Purged";
	}
}

# sub vcl_miss {
#     return (fetch);
# }

sub vcl_miss {
	if (req.request == "PURGE") { 
		purge;
		error 200 "Not in cache";
	}
}

# 
# sub vcl_fetch {
#     if (beresp.ttl <= 0s ||
#         beresp.http.Set-Cookie ||
#         beresp.http.Vary == "*") {
# 		/*
# 		 * Mark as "Hit-For-Pass" for the next 2 minutes
# 		 */
# 		set beresp.ttl = 120 s;
# 		return (hit_for_pass);
#     }
#     return (deliver);
# }

sub vcl_fetch {
	# If backend is not responding, allow replying with a stale response.
	set beresp.grace = 120s;
	
	# Strip cookies for static files:
	if (req.url ~ "\.(jpg|jpeg|gif|png|ico|css|zip|tgz|gz|rar|bz2|pdf|txt|tar|wav|bmp|rtf|js|flv|swf)$") {
		unset beresp.http.set-cookie;
	}

	# X-Cacheable is useful to debug the behaviour of Varnish
	# https://www.varnish-cache.org/trac/wiki/VCLExampleHitMissHeader
	if (beresp.http.Cache-Control ~ "private") {
		 # You are respecting the Cache-Control=private header from the backend
		set beresp.http.X-Cacheable = "NO: Cache-Control=private";
		
		return (hit_for_pass);
	} elsif (beresp.http.Set-Cookie) {
		 # You are respecting the Cache-Control=private header from the backend
		set beresp.http.X-Cacheable = "NO: Set-Cookie";
		
		return (hit_for_pass);
	} elseif (req.http.Cache-Control ~ "no-cache" || req.http.Pragma ~ "no-cache") {
		set beresp.http.X-Cacheable = "NO: Forced by user";

		return (hit_for_pass);
	#} elsif ( beresp.ttl < 1s ) {
	#	# Even if no cache is specified, force a 10s cache.
	#   # Be careful when using this, it may break some websites
	#	set beresp.ttl   = 10s;
	#	set beresp.grace = 10s;
	#	set beresp.http.X-Cacheable = "YES: Auto 10s";
	}
}

# 
# sub vcl_deliver {
#     return (deliver);
# }

sub vcl_deliver {
	# Remove some headers that are useless or may give security information
	remove resp.http.Age;
	remove resp.http.Via;
	remove resp.http.X-Powered-By;

	# Server is needed, so set something generic
	unset resp.http.Server;
	set resp.http.Server = "Webserver";
}

# 
# sub vcl_error {
#     set obj.http.Content-Type = "text/html; charset=utf-8";
#     set obj.http.Retry-After = "5";
#     synthetic {"
# <?xml version="1.0" encoding="utf-8"?>
# <!DOCTYPE html PUBLIC "-#W3C//DTD XHTML 1.0 Strict//EN"
#  "http:#www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
# <html>
#   <head>
#     <title>"} + obj.status + " " + obj.response + {"</title>
#   </head>
#   <body>
#     <h1>Error "} + obj.status + " " + obj.response + {"</h1>
#     <p>"} + obj.response + {"</p>
#     <h3>Guru Meditation:</h3>
#     <p>XID: "} + req.xid + {"</p>
#     <hr>
#     <p>Varnish cache server</p>
#   </body>
# </html>
# "};
#     return (deliver);
# }


sub vcl_error {
	# Remove server for security reasons 
	unset obj.http.Server;
	set obj.http.Server = "Webserver"; 
}


# 
# sub vcl_init {
# 	return (ok);
# }
# 
# sub vcl_fini {
# 	return (ok);
# }

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