Varnish - Historique des versions

G.lalleman le 30 août 2012 à 12:18

2012-08-30T12:18:34Z

← Version précédente		Version du 30 août 2012 à 12:18
Ligne 233 :		Ligne 233 :
	vcl.load will load and compile the new configuration. Compilation will fail and report on syntax errors. Now that the new configuration has been loaded, it can be activated with:		vcl.load will load and compile the new configuration. Compilation will fail and report on syntax errors. Now that the new configuration has been loaded, it can be activated with:
	<pre>vcl.use newconf_1</pre>		<pre>vcl.use newconf_1</pre>
		+
		+	== Monitoring temps réel ==
		+	* Get the top request methods
		+	<pre>varnishtop -i RxRequest</pre>
		+
		+	* Top URLS that missed the cache.
		+	<pre>varnishtop -i TxURL</pre>
		+
		+	* Top URLS that HIT the cache.
		+	<pre>varnishtop -i RxURL</pre>
		+
		+	* All URLs that hit the cache in real time.
		+	<pre>varnishlog -o VCL_call hit \| grep RxURL</pre>
		+
		+	* All URLs that MISSED the cache in real time
		+	<pre>varnishlog -i TxURL</pre>
		+
		+	* Look at an incoming client request of a specific URL:
		+	<pre>varnishlog -c -o RxURL index.html</pre>
		+
		+	* Look at a a backend request of a specific URL:
		+	<pre>varnishlog -b -o TxURL index.html</pre>
		+
		+	* See requests for one specific Hostname:
		+	<pre>varnishlog -c -o RxHeader "Host: cirrii.com"</pre>
		+
		+	* See the age of the cache objects for a specific hostname:
		+	<pre>varnishlog -c -o RxHeader "Host: cirrii.com" \| grep Age</pre>

G.lalleman le 20 juin 2012 à 09:14

2012-06-20T09:14:23Z

← Version précédente		Version du 20 juin 2012 à 09:14
Ligne 1 :		Ligne 1 :
-	~~== Memento ==~~	+	== Configuration et commandes du daemon ==
-	=== Configuration et commandes du daemon ===	+
	* Configuration		* Configuration
	Elle se fait dans le fichier "/etc/default/varnish", nous pourront utiliser les paramètres suivants :		Elle se fait dans le fichier "/etc/default/varnish", nous pourront utiliser les paramètres suivants :
Ligne 27 :		Ligne 26 :
	</pre>		</pre>

-	=== Le language VCL ===	+	== Le language VCL ==
	Rappel : Le code VCL par défaut est toujours présent ! Il est simplement ajouté à nos sections !		Rappel : Le code VCL par défaut est toujours présent ! Il est simplement ajouté à nos sections !

-	==== Subroutines ====	+	=== Subroutines ===
	Ci-dessous les différentes section configurable du cache en utilisant le lagnuage VCL.		Ci-dessous les différentes section configurable du cache en utilisant le lagnuage VCL.

Ligne 47 :		Ligne 46 :
	* vcl_deliver : Appelé juste avant de renvoyé la réponse au client. Permet de modifier, ajouter ou supprimer des headers via l'objet de réponse ("resp").		* vcl_deliver : Appelé juste avant de renvoyé la réponse au client. Permet de modifier, ajouter ou supprimer des headers via l'objet de réponse ("resp").

-	==== Actions ====	+	=== Actions ===
	Actions les plus courantes :		Actions les plus courantes :
	* pass : When you call pass the request and subsequent response will be passed to and from the backend server. It won’t be cached. pass can be called in both vcl_recv and vcl_fetch.		* pass : When you call pass the request and subsequent response will be passed to and from the backend server. It won’t be cached. pass can be called in both vcl_recv and vcl_fetch.
Ligne 55 :		Ligne 54 :
	esi : ESI-process the fetched document.		esi : ESI-process the fetched document.

-	==== Requests, responses and objects ====	+	=== Requests, responses and objects ===
	Le language VCL permet principalement de manipuler 3 structures de données : La requète provenant du client, la réponse du backend et l'objet stocké en cache.		Le language VCL permet principalement de manipuler 3 structures de données : La requète provenant du client, la réponse du backend et l'objet stocké en cache.

Ligne 63 :		Ligne 62 :


-	==== Backends ====	+	=== Backends ===
	* Configuration d'un hôte avec test :		* Configuration d'un hôte avec test :
	<pre>		<pre>
Ligne 92 :		Ligne 91 :
	</pre>		</pre>

-	==== Directors ====	+	=== Directors ===
	* The random director: The random director takes one per director option .retries. This specifies how many tries it will use to find a working backend. The default is the same as the number of backends defined for the director. There is also a per-backend option: weight which defines the portion of traffic to send to the particular backend.		* The random director: The random director takes one per director option .retries. This specifies how many tries it will use to find a working backend. The default is the same as the number of backends defined for the director. There is also a per-backend option: weight which defines the portion of traffic to send to the particular backend.

Ligne 113 :		Ligne 112 :
	</pre>		</pre>

-	==== ACLs ====	+	=== ACLs ===
	Vous pouvez définir des acl afin de restreindre l'utilisation de fonctionnalité. Ci-dessous, l'exemple d'une purge :		Vous pouvez définir des acl afin de restreindre l'utilisation de fonctionnalité. Ci-dessous, l'exemple d'une purge :
	<pre>		<pre>
Ligne 142 :		Ligne 141 :
	</pre>		</pre>

-	=== Mode "Grace" ===	+	== Mode "Grace" ==
	When several clients are requesting the same page Varnish will send one request to the backend and place the others on hold while fetching one copy from the back end.		When several clients are requesting the same page Varnish will send one request to the backend and place the others on hold while fetching one copy from the back end.

Ligne 164 :		Ligne 163 :
	</pre>		</pre>

-	=== Saint mode ===	+	== Saint mode ==
	Sometimes servers get flaky. They start throwing out random errors. You can instruct Varnish to try to handle this in a more-than-graceful way - enter Saint mode. Saint mode enables you to discard a certain page from one backend server and either try another server or serve stale content from cache. Lets have a look at how this can be enabled in VCL:		Sometimes servers get flaky. They start throwing out random errors. You can instruct Varnish to try to handle this in a more-than-graceful way - enter Saint mode. Saint mode enables you to discard a certain page from one backend server and either try another server or serve stale content from cache. Lets have a look at how this can be enabled in VCL:
	<pre>		<pre>
Ligne 176 :		Ligne 175 :
	When we set beresp.saintmode to 10 seconds Varnish will not ask that server for URL for 10 seconds.		When we set beresp.saintmode to 10 seconds Varnish will not ask that server for URL for 10 seconds.

-	=== Troubleshooting ===	+	== Troubleshooting ==

	Trace it under varnishlog, /var/log/syslog, /var/log/messages.		Trace it under varnishlog, /var/log/syslog, /var/log/messages.
Ligne 185 :		Ligne 184 :
	Notice the -d option. It will give you some more information on what is going on.		Notice the -d option. It will give you some more information on what is going on.

-	=== Logs ===	+	== Logs ==
	To see a real-time log dump (in a system-wide Varnish configuration):		To see a real-time log dump (in a system-wide Varnish configuration):
	<pre>varnishlog</pre>		<pre>varnishlog</pre>
Ligne 216 :		Ligne 215 :
	</pre>		</pre>

-	=== Management console ===	+	== Management console ==

	You can access Varnish admin console on your server by:		You can access Varnish admin console on your server by:
Ligne 224 :		Ligne 223 :
	<pre>telnet localhost 6082</pre>		<pre>telnet localhost 6082</pre>

-	=== Purging the cache ===	+	== Purging the cache ==
	This will remove all entries from the Varnish cache:		This will remove all entries from the Varnish cache:
	<pre>url.purge .*</pre>		<pre>url.purge .*</pre>
Ligne 236 :		Ligne 235 :


-	=== Exemples de configurations ===	+	== Exemples de configurations ==

	<pre>		<pre>

G.lalleman le 20 juin 2012 à 08:42

2012-06-20T08:42:46Z

← Version précédente		Version du 20 juin 2012 à 08:42
Ligne 241 :		Ligne 241 :

	</pre>		</pre>
		+
		+	=== Liens ===
		+	* https://www.varnish-cache.org/docs/2.1/reference/vcl.html

	[[Catégorie:Administration serveurs]]		[[Catégorie:Administration serveurs]]

G.lalleman le 20 juin 2012 à 08:40

2012-06-20T08:40:15Z

← Version précédente		Version du 20 juin 2012 à 08:40
Ligne 141 :		Ligne 141 :
	}		}
	</pre>		</pre>
		+
		+	=== Mode "Grace" ===
		+	When several clients are requesting the same page Varnish will send one request to the backend and place the others on hold while fetching one copy from the back end.
		+
		+	If you are serving thousands of hits per second this queue can get huge. Nobody likes to wait so there is a possibility to serve stale content to waiting users. In order to do this we must instruct Varnish to keep the objects in cache beyond their TTL. So, to keep all objects for 30 minutes beyond their TTL use the following VCL:
		+	<pre>
		+	sub vcl_fetch {
		+	set beresp.grace = 5m;
		+	}
		+	sub vcl_recv {
		+	set req.grace = 1m;
		+	}
		+	</pre>
		+	You might wonder why we should keep the objects in the cache for 5 minutes if we are unable to serve them passed 1 minute ? Well, if you have enabled Health checks you can check if the backend is healthy and serve the content for as longer.:
		+	<pre>
		+	if (! req.backend.healthy) {
		+	set req.grace = 5m;
		+	} else {
		+	set req.grace = 1m;
		+	}
		+
		+	</pre>
		+
		+	=== Saint mode ===
		+	Sometimes servers get flaky. They start throwing out random errors. You can instruct Varnish to try to handle this in a more-than-graceful way - enter Saint mode. Saint mode enables you to discard a certain page from one backend server and either try another server or serve stale content from cache. Lets have a look at how this can be enabled in VCL:
		+	<pre>
		+	sub vcl_fetch {
		+	if (beresp.status == 500) {
		+	set beresp.saintmode = 10s;
		+	restart;
		+	}
		+	set beresp.grace = 5m;
		+	}
		+	When we set beresp.saintmode to 10 seconds Varnish will not ask that server for URL for 10 seconds.
		+
		+	=== Troubleshooting ===
		+
		+	Trace it under varnishlog, /var/log/syslog, /var/log/messages.
		+
		+	When Varnish won’t start:
		+	Try to start varnish by:
		+	<pre> varnishd -f /usr/local/etc/varnish/default.vcl -s malloc,1G -T 127.0.0.1:2000 -a 0.0.0.0:8080 -d</pre>
		+	Notice the -d option. It will give you some more information on what is going on.
		+
		+	=== Logs ===
		+	To see a real-time log dump (in a system-wide Varnish configuration):
		+	<pre>varnishlog</pre>
		+	By default, Varnish does not log to any file and keeps the log only in memory. If you want to extract Apache-like logs from varnish, you need to use the varnishncsa utility.
		+	Every poll is recorded in the shared memory log as follows:
		+	<pre>0 Backend_health - b0 Still healthy 4--X-S-RH 9 8 10 0.029291 0.030875 HTTP/1.1 200 Ok</pre>
		+	The fields are:
		+	<pre>
		+	0 -- Constant
		+	Backend_health -- Log record tag
		+	- -- client/backend indication (XXX: wrong! should be 'b')
		+	b0 -- Name of backend (XXX: needs qualifier)
		+	two words indicating state: "Still healthy", "Still sick", "Back healthy", "Went sick"
		+	4--X-S-RH -- Flags indicating how the latest poll went
		+	4 -- IPv4 connection established
		+	6 -- IPv6 connection established
		+	x -- Request transmit failed
		+	X -- Request transmit succeeded
		+	s -- TCP socket shutdown failed
		+	S -- TCP socket shutdown succeeded
		+	r -- Read response failed
		+	R -- Read response succeeded
		+	H -- Happy with result
		+	9 -- Number of good polls in the last .window polls
		+	8 -- .threshold (see above)
		+	10 -- .window (see above)
		+	0.029291 -- Response time this poll or zero if it failed
		+	0.030875 -- Exponential average (r=4) of responsetime for good polls.
		+	HTTP/1.1 200 Ok -- The HTTP response from the backend.
		+	</pre>
		+
		+	=== Management console ===
		+
		+	You can access Varnish admin console on your server by:
		+	# Your system uses a secret handshake file
		+	<pre>varnishadm -T localhost:6082 -S /etc/varnish/secret</pre>
		+	# Your system does not have a secret handshake file
		+	<pre>telnet localhost 6082</pre>
		+
		+	=== Purging the cache ===
		+	This will remove all entries from the Varnish cache:
		+	<pre>url.purge .*</pre>
		+
		+	Loading new VCL for the live varnish daemon:
		+	You can dynamically load and parse a new VCL config file to memory:
		+	<pre>vcl.load <name> <file></pre>
		+	e.g. vcl.load newconf_1 /etc/varnish/newconf.vcl
		+	vcl.load will load and compile the new configuration. Compilation will fail and report on syntax errors. Now that the new configuration has been loaded, it can be activated with:
		+	<pre>vcl.use newconf_1</pre>
		+

	=== Exemples de configurations ===		=== Exemples de configurations ===

G.lalleman le 20 juin 2012 à 08:29

2012-06-20T08:29:19Z

← Version précédente		Version du 20 juin 2012 à 08:29
Ligne 92 :		Ligne 92 :
	</pre>		</pre>

-	* ~~Multiples~~ backend ~~(Round~~ robin~~, random)~~	+	==== Directors ====
-	~~Il faut utiliser une directive~~ director :	+	* The random director: The random director takes one per director option .retries. This specifies how many tries it will use to find a working backend. The default is the same as the number of backends defined for the director. There is also a per-backend option: weight which defines the portion of traffic to send to the particular backend.
		+
		+	* The round-robin director: The round-robin director does not take any options.
		+
		+	* The client director: The client director picks a backend based on the clients identity. You can set the VCL variable client.identity to identify the client by picking up the value of a session cookie or similar. The client director takes one option - retries which set the number of retries the director should take in order to find a healthy backend.
		+
		+	* The hash director: The hash director will pick a backend based on the URL hash value. This is useful if you are using Varnish to load balance in front of other Varnish caches or other web accelerators as objects won’t be duplicated across caches.
		+
		+	* The DNS director: The DNS director can use backends in three different ways. Either like the random or round-robin director or using .list: This will specify 384 backends, all using port 80 and a connection timeout of 0.4s. Options must come before the list of IPs in the .list statement.
	<pre>		<pre>
	director WebSiteA round-robin {		director WebSiteA round-robin {

G.lalleman le 20 juin 2012 à 08:21

2012-06-20T08:21:08Z

← Version précédente		Version du 20 juin 2012 à 08:21
Ligne 28 :		Ligne 28 :

	=== Le language VCL ===		=== Le language VCL ===
		+	Rappel : Le code VCL par défaut est toujours présent ! Il est simplement ajouté à nos sections !
		+
	==== Subroutines ====		==== Subroutines ====
	Ci-dessous les différentes section configurable du cache en utilisant le lagnuage VCL.		Ci-dessous les différentes section configurable du cache en utilisant le lagnuage VCL.

G.lalleman le 20 juin 2012 à 08:06

2012-06-20T08:06:52Z

← Version précédente		Version du 20 juin 2012 à 08:06
Ligne 13 :		Ligne 13 :

	* Commandes		* Commandes
-	Test de la configuration et la recharge si valide :	+	Test de la configuration et la recharge si valide (n'affecte pas le cache) :
	<pre>service varnish reload</pre>		<pre>service varnish reload</pre>
		+	Test et chargement séparé (ce que fait un reload pour nous !) :
		+	<pre>
		+	varnishadm vcl.load
		+	varnishadm vcl.use
		+	</pre>
		+	Purge d'éléments du cache :
		+	<pre>
		+	varnishadm -S /etc/varnish/secret -T :6082 "url.purge .*"
		+	varnishadm -S /etc/varnish/secret -T :6082 'purge req.http.host == "blog.hio.fr"'
		+	varnishadm -S /etc/varnish/secret -T :6082 'purge req.url ~ .(xml\|txt)'
		+	</pre>

	=== Le language VCL ===		=== Le language VCL ===
Ligne 20 :		Ligne 31 :
	Ci-dessous les différentes section configurable du cache en utilisant le lagnuage VCL.		Ci-dessous les différentes section configurable du cache en utilisant le lagnuage VCL.

-	* backends & directors : ~~Backend servers configuration~~. ~~It may be multiple~~ backend ~~& director sections~~.	+	* backends & directors : Configuration des serveurs de backend. Les backends et directeurs sont nommés, il peut y avoir plusieurs backend et/ou directeurs.
		+
		+	* vcl_recv : Appelé des qu'une requête est entièrement reçue et parsée par varnish. Cette routine permet de décidé si l'on doit traiter la requête, de quel manière et sur quel backend si nécessaire. L'objet requête ("req") est accessible et altérable dans cette routine, typiquement pour ajouter, supprimer et modifier les headers et cookies.

-	* ~~vcl_recv~~ : ~~Called at the beginning of a request, after the complete request has been received and parsed~~. ~~Its purpose is to decide whether or not to serve the request~~, ~~how to do it, and, if applicanle, which~~ backend ~~to use~~.	+	* vcl_fetch : Appelé après qu'un document ait été récupéré avec succès d'un backend. Permet de modifier les headers de la réponse avant son insertion en cache. L'objet de requète est encore accessible et il est possible de l'utiliser sur un autre backend (réponse du backend non satisfaisante, en cas de 404 par exemple ...). L'objet de réponse du backend ("beresp") est aussi disponible, c'est cet objet qui sera stocké en cache.

	* vcl_hit : Called after a cache lookup if the requested document was found in the cache.		* vcl_hit : Called after a cache lookup if the requested document was found in the cache.

	* vcl_miss : Called after a cache lookup if the requested document was not found in the cache. Its purpose is to decide whether or not to attempt to retrieve the document from the backend, and which backend to use.		* vcl_miss : Called after a cache lookup if the requested document was not found in the cache. Its purpose is to decide whether or not to attempt to retrieve the document from the backend, and which backend to use.
-
-	* vcl_fetch : Called after a document has been retrieved from the backend, before it is inserted into the cache.

	* vcl_timeout : Called by the reaper thread when a cached document has reached its expiry time.		* vcl_timeout : Called by the reaper thread when a cached document has reached its expiry time.
		+
		+	* vcl_deliver : Appelé juste avant de renvoyé la réponse au client. Permet de modifier, ajouter ou supprimer des headers via l'objet de réponse ("resp").
		+
		+	==== Actions ====
		+	Actions les plus courantes :
		+	* pass : When you call pass the request and subsequent response will be passed to and from the backend server. It won’t be cached. pass can be called in both vcl_recv and vcl_fetch.
		+	* lookup : When you call lookup from vcl_recv you tell Varnish to deliver content from cache even if the request othervise indicates that the request should be passed. You can’t call lookup from vcl_fetch.
		+	pipe : Pipe can be called from vcl_recv as well. Pipe short circuits the client and the backend connections and Varnish will just sit there and shuffle bytes back and forth. Varnish will not look at the data being send back and forth - so your logs will be incomplete. Beware that with HTTP 1.1 a client can send several requests on the same connection and so you should instruct Varnish to add a “Connection: close” header before actually calling pipe.
		+	deliver : Deliver the cached object to the client. Usually called in vcl_fetch.
		+	esi : ESI-process the fetched document.
		+
		+	==== Requests, responses and objects ====
		+	Le language VCL permet principalement de manipuler 3 structures de données : La requète provenant du client, la réponse du backend et l'objet stocké en cache.
		+
		+	* req : The request object. When Varnish has received the request the req object is created and populated. Most of the work you do in vcl_recv you do on or with the req object.
		+	* beresp : The backend respons object. It contains the headers of the object comming from the backend. Most of the work you do in vcl_fetch you do on the beresp object.
		+	obj : The cached object. Mostly a read only object that resides in memory. obj.ttl is writable, the rest is read only.
		+

	==== Backends ====		==== Backends ====
Ligne 74 :		Ligne 103 :
	</pre>		</pre>

		+	==== ACLs ====
		+	Vous pouvez définir des acl afin de restreindre l'utilisation de fonctionnalité. Ci-dessous, l'exemple d'une purge :
		+	<pre>
		+	# Who is allowed to purge....
		+	acl local {
		+	"localhost";
		+	"192.168.1.0"/24; /* and everyone on the local network */
		+	! "192.168.1.23"; /* except for the dialin router */
		+	}
		+	sub vcl_recv {
		+	if (req.request == "PURGE") {
		+	if (client.ip ~ local) {
		+	return(lookup);
		+	}
		+	}
		+	}
		+	sub vcl_hit {
		+	if (req.request == "PURGE") {
		+	set obj.ttl = 0s;
		+	error 200 "Purged.";
		+	}
		+	}
		+	sub vcl_miss {
		+	if (req.request == "PURGE") {
		+	error 404 "Not in cache.";
		+	}
		+	}
		+	</pre>

		+	=== Exemples de configurations ===
		+
		+	<pre>
		+
		+	</pre>

	[[Catégorie:Administration serveurs]]		[[Catégorie:Administration serveurs]]

G.lalleman le 20 juin 2012 à 07:32

2012-06-20T07:32:11Z

← Version précédente		Version du 20 juin 2012 à 07:32
Ligne 1 :		Ligne 1 :
	== Memento ==		== Memento ==
	=== Configuration et commandes du daemon ===		=== Configuration et commandes du daemon ===
		+	* Configuration
	Elle se fait dans le fichier "/etc/default/varnish", nous pourront utiliser les paramètres suivants :		Elle se fait dans le fichier "/etc/default/varnish", nous pourront utiliser les paramètres suivants :
	<pre>		<pre>
Ligne 10 :		Ligne 11 :
	-s <storagetype,options> # where and how to store objects (file for file backend and malloc for memory bakend)		-s <storagetype,options> # where and how to store objects (file for file backend and malloc for memory bakend)
	</pre>		</pre>
		+
		+	* Commandes
		+	Test de la configuration et la recharge si valide :
		+	<pre>service varnish reload</pre>

	=== Le language VCL ===		=== Le language VCL ===
Ligne 27 :		Ligne 32 :
	* vcl_timeout : Called by the reaper thread when a cached document has reached its expiry time.		* vcl_timeout : Called by the reaper thread when a cached document has reached its expiry time.

-	==== Backends ===	+	==== Backends ====
	* Configuration d'un hôte avec test :		* Configuration d'un hôte avec test :
	<pre>		<pre>
Ligne 39 :		Ligne 44 :
	"Connection: close";		"Connection: close";
	}		}
		+	}
		+	backend hostname2 {
		+	.host = "XXX.XXX.XXX.XXX";
		+	.port = "80";
		+	.probe = {
		+	.request =
		+	"GET / HTTP/1.1"
		+	"Host: localhost"
		+	"Connection: close";
		+	.timeout = 120s;
		+	.window = 5;
		+	.threshold = 2;
		+	.interval = 5s;
		+	}
	}		}
	</pre>		</pre>

-	* Round robin	+	* Multiples backend (Round robin, random)
	Il faut utiliser une directive director :		Il faut utiliser une directive director :
	<pre>		<pre>
Ligne 48 :		Ligne 67 :
	{ .backend = hostname1; }		{ .backend = hostname1; }
	{ .backend = hostname2; }		{ .backend = hostname2; }
		+	}
		+	director WebSiteB random {
		+	{ .backend = hostname1; .weight = 1; }
		+	{ .backend = hostname2; .weight = 2; }
	}		}
	</pre>		</pre>
		+
		+

	[[Catégorie:Administration serveurs]]		[[Catégorie:Administration serveurs]]

G.lalleman : Page créée avec « == Memento == === Configuration et commandes du daemon === Elle se fait dans le fichier "/etc/default/varnish", nous pourront utiliser les paramètres suivants :

 -a <[h… »

2012-06-20T07:16:12Z

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== Memento ==
=== Configuration et commandes du daemon ===
Elle se fait dans le fichier "/etc/default/varnish", nous pourront utiliser les paramètres suivants :
<pre>
-a <[hostname]:port> # listen address
-f <filename> # VCL file
-p <parameter=value> # set tunable parameters
-S <secretfile> # authentication secret for management
-T <hostname:port> # Management interface
-s <storagetype,options> # where and how to store objects (file for file backend and malloc for memory bakend)
</pre>

=== Le language VCL ===
==== Subroutines ====
Ci-dessous les différentes section configurable du cache en utilisant le lagnuage VCL.

* backends & directors : Backend servers configuration. It may be multiple backend & director sections.

* vcl_recv : Called at the beginning of a request, after the complete request has been received and parsed. Its purpose is to decide whether or not to serve the request, how to do it, and, if applicanle, which backend to use.

* vcl_hit : Called after a cache lookup if the requested document was found in the cache.

* vcl_miss : Called after a cache lookup if the requested document was not found in the cache. Its purpose is to decide whether or not to attempt to retrieve the document from the backend, and which backend to use.

* vcl_fetch : Called after a document has been retrieved from the backend, before it is inserted into the cache.

* vcl_timeout : Called by the reaper thread when a cached document has reached its expiry time.

==== Backends ===
* Configuration d'un hôte avec test :
<pre>
backend hostname1 {
.host = "XXX.XXX.XXX.XXX";
.port = "80";
.probe = {
.request =
"GET / HTTP/1.1"
"Host: localhost"
"Connection: close";
}
}
</pre>

* Round robin
Il faut utiliser une directive director :
<pre>
director WebSiteA round-robin {
{ .backend = hostname1; }
{ .backend = hostname2; }
}
</pre>

[[Catégorie:Administration serveurs]]