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VCL - Varnish Configuration Language

VCL(7) VCL(7)

NAME

VCL - Varnish Configuration Language

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 <major>.<minor>; 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; duration types will evaluate to false if their value is equal or less than 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 followed by a unit. The number can include a fractional part, e.g. 1.5s. The supported units are:
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 to probes and regular backend requests if they have no such header.
.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. Allowed values are 1 and 2.
.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 vmod_directors(3) man page for more information.

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.

bereq

bereq
Type: HTTP
 
Readable from: backend
 
The entire backend request HTTP data structure


 
bereq.backend
Type: BACKEND
 
Readable from: vcl_pipe, backend
 
Writable from: vcl_pipe, backend
 
This is the backend or director we attempt to fetch from. When set to a director, reading this variable returns an actual backend if the director has resolved immediately, or the director otherwise. When used in string context, returns the name of the director or backend, respectively.


 
bereq.between_bytes_timeout
Type: DURATION
 
Readable from: backend
 
Writable from: backend
 
The time in seconds to wait between each received byte from the backend. Not available in pipe mode.


 
bereq.body
Type: BODY
 
Writable from: vcl_backend_fetch
 
The request body.


 
bereq.connect_timeout
Type: DURATION
 
Readable from: vcl_pipe, backend
 
Writable from: vcl_pipe, backend
 
The time in seconds to wait for a backend connection.


 
bereq.first_byte_timeout
Type: DURATION
 
Readable from: backend
 
Writable from: backend
 
The time in seconds to wait for the first byte from the backend. Not available in pipe mode.


 
bereq.hash
Type: BLOB
 
Readable from: vcl_pipe, backend
 
The hash key of this request.


 
bereq.http.
Type: HEADER
 
Readable from: vcl_pipe, backend
 
Writable from: vcl_pipe, backend
 
The corresponding HTTP header.


 
bereq.is_bgfetch
Type: BOOL
 
Readable from: backend
 
True for background fetches.


 
bereq.method
Type: STRING
 
Readable from: vcl_pipe, backend
 
Writable from: vcl_pipe, backend
 
The request type (e.g. "GET", "HEAD").


 
bereq.proto
Type: STRING
 
Readable from: vcl_pipe, backend
 
Writable from: vcl_pipe, backend
 
The HTTP protocol version used to talk to the server.


 
bereq.retries
Type: INT
 
Readable from: backend
 
A count of how many times this request has been retried.


 
bereq.uncacheable
Type: BOOL
 
Readable from: backend
 
Indicates whether this request is uncacheable due to a pass in the client side or a hit on an hit-for-pass object.


 
bereq.url
Type: STRING
 
Readable from: vcl_pipe, backend
 
Writable from: vcl_pipe, backend
 
The requested URL.


 
bereq.xid
Type: STRING
 
Readable from: backend
 
Unique ID of this request.


beresp

beresp
Type: HTTP
 
Readable from: vcl_backend_response, vcl_backend_error
 
The entire backend response HTTP data structure


 
beresp.age
Type: DURATION
 
Readable from: vcl_backend_response, vcl_backend_error
 
The age of the object.


 
beresp.backend
Type: BACKEND
 
Readable from: vcl_backend_response, vcl_backend_error
 
This is the backend we fetched from. If bereq.backend was set to a director, this will be the backend selected by the director. When used in string context, returns its name.


 
beresp.backend.ip
Type: IP
 
Readable from: vcl_backend_response
 
IP of the backend this response was fetched from.


 
beresp.backend.name
Type: STRING
 
Readable from: vcl_backend_response, vcl_backend_error
 
Name of the backend this response was fetched from. Same as beresp.backend.


 
beresp.body
Type: BODY
 
Writable from: vcl_backend_error
 
The response body.


 
beresp.do_esi
Type: BOOL
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
Boolean. ESI-process the object after fetching it. Defaults to false. Set it to true to parse the object for ESI directives. Will only be honored if req.esi is true.


 
beresp.do_gunzip
Type: BOOL
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
Boolean. Unzip the object before storing it in the cache. Defaults to false.


 
beresp.do_gzip
Type: BOOL
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
Boolean. Gzip the object before storing it. Defaults to false. When http_gzip_support is on Varnish will request already compressed content from the backend and as such compression in Varnish is not needed.


 
beresp.do_stream
Type: BOOL
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
Deliver the object to the client while fetching the whole object into varnish. For uncacheable objects, storage for parts of the body which have been sent to the client may get freed early, depending on the storage engine used.


 
beresp.grace
Type: DURATION
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
Set to a period to enable grace.


 
beresp.http.
Type: HEADER
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
The corresponding HTTP header.


 
beresp.keep
Type: DURATION
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
Set to a period to enable conditional backend requests.
 
The keep time is cache lifetime in addition to the ttl.
 
Objects with ttl expired but with keep time left may be used to issue conditional (If-Modified-Since / If-None-Match) requests to the backend to refresh them.


 
beresp.proto
Type: STRING
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
The HTTP protocol version used the backend replied with.


 
beresp.reason
Type: STRING
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
The HTTP status message returned by the server.


 
beresp.status
Type: INT
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
The HTTP status code returned by the server.
 
Status codes >1000 can be set for vcl-internal purposes and will be taken modulo 1000 on delivery.


 
beresp.storage
Type: STEVEDORE
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
The storage backend to use to save this object.


 
beresp.storage_hint
Type: STRING
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
Deprecated. Hint to Varnish that you want to save this object to a particular storage backend. Use beresp.storage instead.


 
beresp.ttl
Type: DURATION
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
The object's remaining time to live, in seconds.


 
beresp.uncacheable
Type: BOOL
 
Readable from: vcl_backend_response, vcl_backend_error
 
Writable from: vcl_backend_response, vcl_backend_error
 
Inherited from bereq.uncacheable, see there.
 
Setting this variable makes the object uncacheable, which may get stored as a hit-for-miss object in the cache.
 
Clearing the variable has no effect and will log the warning "Ignoring attempt to reset beresp.uncacheable".


 
beresp.was_304
Type: BOOL
 
Readable from: vcl_backend_response, vcl_backend_error
 
Boolean. If this is a successful 304 response to a backend conditional request refreshing an existing cache object.


client

client.identity
Type: STRING
 
Readable from: client
 
Writable from: client
 
Identification of the client, used to load balance in the client director. Defaults to the client's IP address.


 
client.ip
Type: IP
 
Readable from: client, backend
 
The client's IP address.


local

local.ip
Type: IP
 
Readable from: client, backend
 
The IP address of the local end of the TCP connection.


now

now
Type: TIME
 
Readable from: all
 
The current time, in seconds since the epoch. When used in string context it returns a formatted string.


obj

obj.age
Type: DURATION
 
Readable from: vcl_hit, vcl_deliver
 
The age of the object.


 
obj.grace
Type: DURATION
 
Readable from: vcl_hit, vcl_deliver
 
The object's remaining grace period in seconds.


 
obj.hits
Type: INT
 
Readable from: vcl_hit, vcl_deliver
 
The count of cache-hits on this object. A value of 0 indicates a cache miss.


 
obj.http.
Type: HEADER
 
Readable from: vcl_hit
 
The corresponding HTTP header.


 
obj.keep
Type: DURATION
 
Readable from: vcl_hit, vcl_deliver
 
The object's remaining keep period in seconds.


 
obj.proto
Type: STRING
 
Readable from: vcl_hit
 
The HTTP protocol version stored with the object.


 
obj.reason
Type: STRING
 
Readable from: vcl_hit
 
The HTTP reason phrase stored with the object.


 
obj.status
Type: INT
 
Readable from: vcl_hit
 
The HTTP status code stored with the object.


 
obj.ttl
Type: DURATION
 
Readable from: vcl_hit, vcl_deliver
 
The object's remaining time to live, in seconds.


 
obj.uncacheable
Type: BOOL
 
Readable from: vcl_deliver
 
Whether the object is uncacheable (pass, hit-for-pass or hit-for-miss).


remote

remote.ip
Type: IP
 
Readable from: client, backend
 
The IP address of the other end of the TCP connection. This can either be the clients IP, or the outgoing IP of a proxy server.


req

req
Type: HTTP
 
Readable from: client
 
The entire request HTTP data structure


 
req.backend_hint
Type: BACKEND
 
Readable from: client
 
Writable from: client
 
Set bereq.backend to this if we attempt to fetch. When set to a director, reading this variable returns an actual backend if the director has resolved immediately, or the director otherwise. When used in string context, returns the name of the director or backend, respectively. Note: backend_hint gets reset to the default backend by restarts!


 
req.can_gzip
Type: BOOL
 
Readable from: client
 
Does the client accept the gzip transfer encoding.


 
req.esi
Type: BOOL
 
Readable from: client
 
Writable from: client
 
Boolean. Set to false to disable ESI processing regardless of any value in beresp.do_esi. Defaults to true. This variable is subject to change in future versions, you should avoid using it.


 
req.esi_level
Type: INT
 
Readable from: client
 
A count of how many levels of ESI requests we're currently at.


 
req.hash
Type: BLOB
 
Readable from: vcl_hit, vcl_miss, vcl_pass, vcl_purge, vcl_deliver
 
The hash key of this request.


 
req.hash_always_miss
Type: BOOL
 
Readable from: vcl_recv
 
Writable from: vcl_recv
 
Force a cache miss for this request. If set to true Varnish will disregard any existing objects and always (re)fetch from the backend.


 
req.hash_ignore_busy
Type: BOOL
 
Readable from: vcl_recv
 
Writable from: vcl_recv
 
Ignore any busy object during cache lookup. You would want to do this if you have two server looking up content from each other to avoid potential deadlocks.


 
req.http.
Type: HEADER
 
Readable from: client
 
Writable from: client
 
The corresponding HTTP header.


 
req.method
Type: STRING
 
Readable from: client
 
Writable from: client
 
The request type (e.g. "GET", "HEAD").


 
req.proto
Type: STRING
 
Readable from: client
 
Writable from: client
 
The HTTP protocol version used by the client.


 
req.restarts
Type: INT
 
Readable from: client
 
A count of how many times this request has been restarted.


 
req.storage
Type: STEVEDORE
 
Readable from: vcl_recv
 
Writable from: vcl_recv
 
The storage backend to use to save this request body.


 
req.ttl
Type: DURATION
 
Readable from: client
 
Writable from: client
 
Upper limit on the object age for cache lookups to return hit.
 
Usage of req.ttl should be replaced with a check on obj.ttl in vcl_hit, returning miss when needed, but this currently hits bug #1799, so an additional workaround is required.
 
Deprecated and scheduled for removal with varnish release 7.


 
req.url
Type: STRING
 
Readable from: client
 
Writable from: client
 
The requested URL.


 
req.xid
Type: STRING
 
Readable from: client
 
Unique ID of this request.


req_top

req_top.http.
Type: HEADER
 
Readable from: client
 
HTTP headers of the top-level request in a tree of ESI requests. Identical to req.http. in non-ESI requests.


 
req_top.method
Type: STRING
 
Readable from: client
 
The request method of the top-level request in a tree of ESI requests. (e.g. "GET", "HEAD"). Identical to req.method in non-ESI requests.


 
req_top.proto
Type: STRING
 
Readable from: client
 
HTTP protocol version of the top-level request in a tree of ESI requests. Identical to req.proto in non-ESI requests.


 
req_top.url
Type: STRING
 
Readable from: client
 
The requested URL of the top-level request in a tree of ESI requests. Identical to req.url in non-ESI requests.


resp

resp
Type: HTTP
 
Readable from: vcl_deliver, vcl_synth
 
The entire response HTTP data structure.


 
resp.body
Type: BODY
 
Writable from: vcl_synth
 
The response body.


 
resp.http.
Type: HEADER
 
Readable from: vcl_deliver, vcl_synth
 
Writable from: vcl_deliver, vcl_synth
 
The corresponding HTTP header.


 
resp.is_streaming
Type: BOOL
 
Readable from: vcl_deliver, vcl_synth
 
Returns true when the response will be streamed from the backend.


 
resp.proto
Type: STRING
 
Readable from: vcl_deliver, vcl_synth
 
Writable from: vcl_deliver, vcl_synth
 
The HTTP protocol version to use for the response.


 
resp.reason
Type: STRING
 
Readable from: vcl_deliver, vcl_synth
 
Writable from: vcl_deliver, vcl_synth
 
The HTTP status message that will be returned.


 
resp.status
Type: INT
 
Readable from: vcl_deliver, vcl_synth
 
Writable from: vcl_deliver, vcl_synth
 
The HTTP status code that will be returned.
 
Assigning a HTTP standardized code to resp.status will also set resp.reason to the corresponding status message.
 
resp.status 200 will get changed into 304 by core code after a return(deliver) from vcl_deliver for conditional requests to cached content if validation succeeds.


server

server.hostname
Type: STRING
 
Readable from: all
 
The host name of the server.


 
server.identity
Type: STRING
 
Readable from: all
 
The identity of the server, as set by the -i parameter. If the -i parameter is not passed to varnishd, server.identity will be set to the hostname of the machine.


 
server.ip
Type: IP
 
Readable from: client, backend
 
The IP address of the socket on which the client connection was received.


storage

storage.<name>.free_space
Type: BYTES
 
Readable from: client, backend
 
Free space available in the named stevedore. Only available for the malloc stevedore.


 
storage.<name>.used_space
Type: BYTES
 
Readable from: client, backend
 
Used space in the named stevedore. Only available for the malloc stevedore.


 
storage.<name>.happy
Type: BOOL
 
Readable from: client, backend
 
Health status for the named stevedore. Not available in any of the current stevedores.


Functions

The following built-in functions are available:

ban(STRING)

Invalidates all objects in cache that match the given expression with the ban mechanism.
 
The format of STRING is:
 
<field> <operator> <arg> [&& <field> <oper> <arg> ...]


<field>:
req.url: The request url
req.http.*: Any request header
obj.status: The cache object status
obj.http.*: Any cache object header

<operator>:
==: <field> and <arg> are equal strings (case sensitive)
!=: <field> and <arg> are unequal strings (case sensitive)
~: <field> matches the regular expression <arg>
!~:<field> does not match the regular expression <arg>

<arg>: Either a literal string or a regular expression. Note that <arg> does not use any of the string delimiters like " or {"..."} used elsewhere in varnish. To match against strings containing whitespace, regular expressions containing \s can be used.

 
Expressions can be chained using the and operator &&. For or semantics, use several bans.
 
The unset <field> is not equal to any string, such that, for a non-existing header, the operators == and ~ always evaluate as false, while the operators != and !~ always evaluate as true, respectively, for any value of <arg>.


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.


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.


 
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

varnishd(1)
vmod_directors(3)
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 Lyngstøl, Lasse Karstensen and possibly others. 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