.. role:: ref(emphasis)
.. _vcl(7):
===
VCL
===
------------------------------
Varnish Configuration Language
------------------------------
:Manual section: 7
DESCRIPTION
===========
The VCL language is a small domain-specific language designed to be
used to describe request handling and document caching policies for
Varnish Cache.
When a new configuration is loaded, the varnishd management process
translates the VCL code to C and compiles it to a shared object which
is then loaded into the server process.
This document focuses on the syntax of the VCL language. For a full
description of syntax and semantics, with ample examples, please see
the online documentation at https://www.varnish-cache.org/docs/ .
Starting with Varnish 4.0, each VCL file must start by declaring its version
with "vcl X.Y;" marker at the top of the file. See more about this
under Versioning below.
Operators
---------
The following operators are available in VCL:
=
Assignment operator.
==
Comparison.
~
Match. Can either be used with regular expressions or ACLs.
!
Negation.
&&
Logical and.
||
Logical or.
Conditionals
------------
VCL has *if* and *else* statements. Nested logic can be implemented
with the *elseif* statement (*elsif*/*elif*/*else if* are equivalent).
Note that there are no loops or iterators of any kind in VCL.
Strings, booleans, time, duration, integers and real numbers
------------------------------------------------------------
These are the data types in Varnish. You can *set* or *unset* these.
Example::
set req.http.User-Agent = "unknown";
unset req.http.Range;
Strings
~~~~~~~
Basic strings are enclosed in double quotes (" ... "), and may not contain
newlines. Long strings are enclosed in {" ... "}. They may contain any
character including single double quotes ("), newline and other control
characters except for the NUL (0x00) character.
Booleans
~~~~~~~~
Booleans can be either *true* or *false*. In addition, in a boolean
context some data types will evaluate to *true* or *false* depending on
their value.
String types will evaluate to *false* if they are empty; backend types
will evalute to *false* if they don't have a backend assigned; integer
types will evaluate to *false* if their value is zero.
Time
~~~~
VCL has time. A duration can be added to a time to make another time.
In string context they return a formatted string in RFC1123 format
(e.g. Sun, 06 Nov 1994 08:49:37 GMT).
The keyword *now* returns a time representing the current time in seconds
since the Epoch.
Durations
~~~~~~~~~
Durations are defined by a number and a designation. The number can be a real
so 1.5w is allowed.
ms
milliseconds
s
seconds
m
minutes
h
hours
d
days
w
weeks
y
years
Integers
~~~~~~~~
Certain fields are integers, used as expected. In string context they
return a string.
Real numbers
~~~~~~~~~~~~
VCL understands real numbers. As with integers, when used in a string
context they will return a string.
Regular Expressions
-------------------
Varnish uses Perl-compatible regular expressions (PCRE). For a
complete description please see the pcre(3) man page.
To send flags to the PCRE engine, such as to do case insensitive matching, add
the flag within parens following a question mark, like this::
# If host is NOT example dot com..
if (req.http.host !~ "(?i)example.com$") {
...
}
Include statement
-----------------
To include a VCL file in another file use the include keyword::
include "foo.vcl";
Import statement
----------------
The *import* statement is used to load Varnish Modules (VMODs.)
Example::
import std;
sub vcl_recv {
std.log("foo");
}
Comments
--------
Single lines of VCL can be commented out using // or #. Multi-line blocks can
be commented out with \/\* block \/\*.
Example::
sub vcl_recv {
// Single line of out-commented VCL.
# Another way of commenting out a single line.
/*
Multi-line block of commented-out VCL.
*/
}
Backend definition
------------------
A backend declaration creates and initialises a named backend object. A
declaration start with the keyword *backend* followed by the name of the
backend. The actual declaration is in curly brackets, in a key/value fashion.::
backend name {
.attribute = "value";
}
The only mandatory attribute is *host*. The attributes will inherit
their defaults from the global parameters. The following attributes
are available:
host (mandatory)
The host to be used. IP address or a hostname that resolves to a
single IP address.
port
The port on the backend that Varnish should connect to.
host_header
A host header to add.
connect_timeout
Timeout for connections.
first_byte_timeout
Timeout for first byte.
between_bytes_timeout
Timeout between bytes.
probe
Attach a probe to the backend. See `Probes`_
proxy_header
The PROXY protocol version Varnish should use when connecting to
this backend.
max_connections
Maximum number of open connections towards this backend. If
Varnish reaches the maximum Varnish it will start failing
connections.
Backends can be used with *directors*. Please see the
:ref:`vmod_directors(3)` man page for more information.
.. _reference-vcl_probes:
Probes
------
Probes will query the backend for status on a regular basis and mark
the backend as down it they fail. A probe is defined as this::
probe name {
.attribute = "value";
}
The probe named `default` is special and will be used for all backends
which do not explicitly reference a probe.
There are no mandatory options. These are the options you can set:
url
The URL to query. Defaults to "/".
request
Specify a full HTTP request using multiple strings. .request will
have \\r\\n automatically inserted after every string. If
specified, .request will take precedence over .url.
expected_response
The expected HTTP response code. Defaults to 200.
timeout
The timeout for the probe. Default is 2s.
interval
How often the probe is run. Default is 5s.
initial
How many of the polls in .window are considered good when Varnish
starts. Defaults to the value of threshold - 1. In this case, the
backend starts as sick and requires one single poll to be
considered healthy.
window
How many of the latest polls we examine to determine backend health.
Defaults to 8.
threshold
How many of the polls in .window must have succeeded for us to
consider the backend healthy. Defaults to 3.
Access Control List (ACL)
-------------------------
An Access Control List (ACL) declaration creates and initialises a named access
control list which can later be used to match client addresses::
acl localnetwork {
"localhost"; # myself
"192.0.2.0"/24; # and everyone on the local network
! "192.0.2.23"; # except for the dial-in router
}
If an ACL entry specifies a host name which Varnish is unable to
resolve, it will match any address it is compared to. Consequently,
if it is preceded by a negation mark, it will reject any address it is
compared to, which may not be what you intended. If the entry is
enclosed in parentheses, however, it will simply be ignored.
To match an IP address against an ACL, simply use the match operator::
if (client.ip ~ localnetwork) {
return (pipe);
}
VCL objects
-----------
A VCL object can be instantiated with the *new* keyword::
sub vcl_init {
new b = directors.round_robin()
b.add_backend(node1);
}
This is only available in vcl_init.
Subroutines
-----------
A subroutine is used to group code for legibility or reusability::
sub pipe_if_local {
if (client.ip ~ localnetwork) {
return (pipe);
}
}
Subroutines in VCL do not take arguments, nor do they return
values. The built in subroutines all have names beginning with vcl\_,
which is reserved.
To call a subroutine, use the call keyword followed by the subroutine's name::
sub vcl_recv {
call pipe_if_local;
}
Return statements
~~~~~~~~~~~~~~~~~
The ongoing vcl\_* subroutine execution ends when a return(*action*) statement
is made.
The *action* specifies how execution should proceed. The context defines
which actions are available.
Multiple subroutines
~~~~~~~~~~~~~~~~~~~~
If multiple subroutines with the name of one of the built-in ones are defined,
they are concatenated in the order in which they appear in the source.
The built-in VCL distributed with Varnish will be implicitly concatenated
when the VCL is compiled.
Variables
---------
In VCL you have access to certain variable objects. These contain
requests and responses currently being worked on. What variables are
available depends on context.
.. include:: ../include/vcl_var.rst
Functions
---------
The following built-in functions are available:
ban(expression)
Invalidates all objects in cache that match the expression with the
ban mechanism.
hash_data(input)
Adds an input to the hash input. In the built-in VCL hash_data()
is called on the host and URL of the *request*. Available in vcl_hash.
synthetic(STRING)
Prepare a synthetic response body containing the STRING. Available in
vcl_synth and vcl_backend_error.
.. list above comes from struct action_table[] in vcc_action.c.
regsub(str, regex, sub)
Returns a copy of str with the first occurrence of the regular
expression regex replaced with sub. Within sub, \\0 (which can
also be spelled \\&) is replaced with the entire matched string,
and \\n is replaced with the contents of subgroup n in the
matched string.
regsuball(str, regex, sub)
As regsub() but this replaces all occurrences.
.. regsub* is in vcc_expr.c
For converting or casting VCL values between data types use the functions
available in the std VMOD.
Versioning
==========
Multiple versions of the VCL syntax can coexist within certain
constraints.
The VCL syntax version at the start of VCL file specified with ''-f''
sets the hard limit that cannot be exceeded anywhere, and it selects
the appropriate version of the builtin VCL.
That means that you can never include "vcl 9.1;" from "vcl 8.7;", but
the opposite *may* be possible, to the extent the compiler supports it.
Files pulled in via ``include`` do not need to have a "vcl X.Y;" but
it may be a good idea to do it anyway, to not have surprises in the
future. The syntax version set in an included file only applies to
that file and any files it includes - unless these set their own VCL
syntax version.
The version of Varnish this file belongs to supports syntax 4.0 only.
EXAMPLES
========
For examples, please see the online documentation.
SEE ALSO
========
* :ref:`varnishd(1)`
* :ref:`vmod_directors(3)`
* :ref:`vmod_std(3)`
HISTORY
=======
VCL was developed by Poul-Henning Kamp in cooperation with Verdens
Gang AS, Redpill Linpro and Varnish Software. This manual page is
written by Per Buer, Poul-Henning Kamp, Martin Blix Grydeland,
Kristian Lyngst?l, Lasse Karstensen and possibly others.
COPYRIGHT
=========
This document is licensed under the same license as Varnish
itself. See LICENSE for details.
* Copyright (c) 2006 Verdens Gang AS
* Copyright (c) 2006-2015 Varnish Software AS
Henceforth, whatever our philosopher says about Matter will apply to extension and to extension alone. It cannot be apprehended by sight, nor by hearing, nor by smell, nor by taste, for it is neither colour, nor sound, nor odour, nor juice. Neither can it be touched, for it is not a body, but it becomes corporeal on being blended with sensible qualities. And, in a later essay, he describes it as receiving all things and letting them depart again without retaining the slightest trace of their presence.483 Why then, it may be asked, if Plotinus meant extension, could he not say so at once, and save us all this trouble in hunting out his meaning? There were very good reasons why he should not. In the first place, he wished to express himself, so far as possible, in Aristotelian phraseology, and this was incompatible with the reduction of Matter to extension. In the next place, the idea of an infinite void had been already appropriated by the Epicureans, to whose system he was bitterly opposed. And, finally, the extension of ordinary327 experience had not the absolute generality which was needed in order to bring Matter into relation with that ultimate abstraction whence, like everything else, it has now to be derived. That the millionaire was genuine, ¡°in person and not a caricature,¡± as Dick put it, was evident. Both the nurse, his relative, and his wife, were chatting with him as Jeff delivered the heavy packed ball made up of the gum. 233 "I guess not," said Landor, tolerantly, as he turned[Pg 106] his horse over to his orderly; "but, anyway," he added to Ellton, "we had a picnic¡ªof a sort." Si, unable to think of anything better, went with him. The train had stopped on a switch, and seemed likely to rust fast to the rails, from the way other trains were going by in both directions. The bridge gang, under charge of a burly, red-faced young Englishman, was in the rear car, with their tools, equipments, bedding and cooking utensils. THE DEACON HAS SOME EXPERIENCES WITH THE QUADRUPED. "You are not within a mile of the truth. I know it. Look here: I believe that is Gen. Rosecrans's own cow. She's gone, and I got an order to look around for her. I've never seen her, but from the description given me I believe that's she. Who brought her here?" "Deacon, these brothers and sisters who have come here with me to-night are, like myself, deeply interested in the moral condition of the army, where we all have sons or kinsmen. Now, can't you sit right there and tell us of your observations and experiences, as a Christian man and father, from day to day, of every day that you were down there? Tell us everything, just as it happened each day, that we may be able to judge for ourselves." HAS AN ENCOUNTER WITH THE PROVOST-MARSHAL. "Wonder which one o' them is the 200th Injianny's?" said Si to Shorty. "And your mother, and Harry?" The daughter must be the girl who was talking to him now. She sat on a little stool by the fire, and had brought out some sewing. "Over at Grandturzel¡ªcan't see wot's burning from here. Git buckets and come!" These things, however, gave little concern to the worthy who commanded the Kentish division. Tyler, though an excellent blacksmith, possessed few of the qualities requisite for forming a good general. Provided there was no very sensible diminution in the number of his followers, he cared not a straw for the score or two who, after quarrelling, or perhaps fighting, withdrew in such disgust that they vowed rather to pay the full tax for ever than submit to the insolence of the rebels. One man could fight as well as another, reasoned he; and, provided he was obeyed, what mattered it by whom. Dick went and Tom came¡ªit was sure to be all one in the end. But this burst of indignation soon passed away, and upon the suggestion of the prudent Sir Robert Hailes, he sent an evasive answer, with a command that the Commons should attend him at Windsor on the Sunday following. That it was a stratagem to gain entrance to the Tower, was the opinion of several, but, after much discussion, it was decided that the man should be admitted, and that the monk should be exhibited merely to intimidate the rebels, until the result of this promised communication should be known. HoMEŮͬÐÔÁµcbcb
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