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 <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 evaluate 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 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 /. Mutually exclusive with .request
.request

Specify a full HTTP request using multiple strings. .request will have \r\n automatically inserted after every string. Mutually exclusive with .url.

Note that probes require the backend to complete sending the response and close the connection within the specified timeout, so .request will, for HTTP/1.1, most likely need to contain a "Connection: close" string.

.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 to consider the backend to be 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

Variables provide read, write and delete access to almost all aspects of the work at hand.

Reading a variable is done simply by using its name in VCL:

if (client.ip ~ bad_guys) {
    return (synth(400));
}

Writing a variable, where this is possible, is done with a set statement:

set resp.http.never = "Let You Down";

Similarly, deleting a variable, for the few variables where this is possible, is done with a unset statement:

unset req.http.cookie;

Which operations are possible on each variable is described below, often with the shorthand "backend" which covers the vcl_backend_* methods and "client" which covers the rest, except vcl_init and vcl_fini.

When setting a variable, the right hand side of the equal sign must have the variables type, you cannot assign a STRING to a variable of type NUMBER, even if the string is "42". (Explicit conversion functions can be found in vmod_std).

local, server, remote and client

These variables describe the network connection between the client and varnishd.

Without PROXY protocol:

     client    server
     remote    local
       v          v
CLIENT ------------ VARNISHD

With PROXY protocol:

     client    server   remote     local
       v          v       v          v
CLIENT ------------ PROXY ------------ VARNISHD

local.endpoint

Type: STRING

Readable from: client

The address of the '-a' socket the session was accepted on.

If the argument was -a foo=:81 this would be ":81"

local.socket

Type: STRING

Readable from: client

The name of the '-a' socket the session was accepted on.

If the argument was -a foo=:81 this would be "foo".

Note that all '-a' gets a default name on the form a%d if no name is provided.

local.ip

Type: IP

Readable from: client, backend

The IP address (and port number) of the local end of the TCP connection, for instance 192.168.1.1:81

If the connection is a UNIX domain socket, the value will be 0.0.0.0:0

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.

If the connection is a UNIX domain socket, the value will be 0.0.0.0:0

client.ip

Type: IP

Readable from: client, backend

The client's IP address, either the same as local.ip or what the PROXY protocol told us.

client.identity

Type: STRING

Readable from: client

Writable from: client

Identification of the client, used to load balance in the client director. Defaults to client.ip

This variable can be overwritten with more precise information, for instance extracted from a Cookie: header.

server.ip

Type: IP

Readable from: client, backend

The IP address of the socket on which the client connection was received, either the same as server.ip or what the PROXY protocol told us.

server.hostname

Type: STRING

Readable from: all

The host name of the server, as returned by the gethostname(3) system function.

server.identity

Type: STRING

Readable from: all

The identity of the server, as set by the -i parameter.

If an -i parameter is not passed to varnishd, the return value from gethostname(3) system function will be used.

req and req_top

These variables describe the present request, and when ESI:include requests are being processed, req_top points to the request received from the client.

req

Type: HTTP

Readable from: client

The entire request HTTP data structure. Mostly useful for passing to VMODs.

req.method

Type: STRING

Readable from: client

Writable from: client

The request method (e.g. "GET", "HEAD", ...)

req.hash

Type: BLOB

Readable from: vcl_hit, vcl_miss, vcl_pass, vcl_purge, vcl_deliver

The hash key of this request. Mostly useful for passing to VMODs, but can also be useful for debugging hit/miss status.

req.url

Type: STRING

Readable from: client

Writable from: client

The requested URL, for instance "/robots.txt".

req.proto VCL <= 4.0

Type: STRING

Readable from: client

Writable from: client

The HTTP protocol version used by the client, usually "HTTP/1.1" or "HTTP/2.0".

req.proto VCL >= 4.1

Type: STRING

Readable from: client

The HTTP protocol version used by the client, usually "HTTP/1.1" or "HTTP/2.0".

req.http.*

Type: HEADER

Readable from: client

Writable from: client

Unsetable from: client

The headers of request, things like req.http.date.

The RFCs allow multiple headers with the same name, and both set and unset will remove all headers with the name given.

req.restarts

Type: INT

Readable from: client

A count of how many times this request has been restarted.

req.storage

Type: STEVEDORE

Readable from: client

Writable from: client

The storage backend to use to save this request body.

req.esi_level

Type: INT

Readable from: client

A count of how many levels of ESI requests we're currently at.

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.xid

Type: STRING

Readable from: client

Unique ID of this request.

req.esi VCL <= 4.0

Type: BOOL

Readable from: client

Writable from: client

Set to false to disable ESI processing regardless of any value in beresp.do_esi. Defaults to true. This variable is replaced by resp.do_esi in VCL 4.1.

req.can_gzip

Type: BOOL

Readable from: client

True if the client provided gzip or x-gzip in the Accept-Encoding header.

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.

req.hash_ignore_busy

Type: BOOL

Readable from: client

Writable from: client

Default: false

Ignore any busy object during cache lookup.

You only want to do this when you have two server looking up content sideways from each other to avoid deadlocks.

req.hash_always_miss

Type: BOOL

Readable from: client

Writable from: client

Default: false

Force a cache miss for this request, even if perfectly good matching objects are in the cache.

This is useful to force-update the cache without invalidating existing entries in case the fetch fails.

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.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.

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.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.

bereq

This is the request we send to the backend, it is built from the clients req.* fields by filtering out "per-hop" fields which should not be passed along (Connection:, Range: and similar).

Slightly more fields are allowed through for pass fetches than for miss fetches, for instance Range.

bereq

Type: HTTP

Readable from: backend

The entire backend request HTTP data structure. Mostly useful as argument to VMODs.

bereq.xid

Type: STRING

Readable from: backend

Unique ID of this request.

bereq.retries

Type: INT

Readable from: backend

A count of how many times this request has been retried.

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.body

Type: BODY

Unsetable from: vcl_backend_fetch

The request body, only present on pass requests.

Unset will also remove bereq.http.Content-Length.

bereq.hash

Type: BLOB

Readable from: vcl_pipe, backend

The hash key of this request, a copy of req.hash.

bereq.method

Type: STRING

Readable from: vcl_pipe, backend

Writable from: vcl_pipe, backend

The request type (e.g. "GET", "HEAD").

Regular (non-pipe, non-pass) fetches are always "GET"

bereq.url

Type: STRING

Readable from: vcl_pipe, backend

Writable from: vcl_pipe, backend

The requested URL, copied from req.url

bereq.proto VCL <= 4.0

Type: STRING

Readable from: vcl_pipe, backend

Writable from: vcl_pipe, backend

The HTTP protocol version, "HTTP/1.1" unless a pass or pipe request has "HTTP/1.0" in req.proto

bereq.proto VCL >= 4.1

Type: STRING

Readable from: vcl_pipe, backend

The HTTP protocol version, "HTTP/1.1" unless a pass or pipe request has "HTTP/1.0" in req.proto

bereq.http.*

Type: HEADER

Readable from: vcl_pipe, backend

Writable from: vcl_pipe, backend

Unsetable from: vcl_pipe, backend

The headers to be sent to the backend.

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.connect_timeout

Type: DURATION

Readable from: vcl_pipe, backend

Writable from: vcl_pipe, backend

The time in seconds to wait for a backend connection to be established.

bereq.first_byte_timeout

Type: DURATION

Readable from: backend

Writable from: backend

The time in seconds to wait getting the first byte back from the backend. Not available in pipe mode.

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.is_bgfetch

Type: BOOL

Readable from: backend

True for fetches where the client got a hit on an object in grace, and this fetch was kicked of in the background to get a fresh copy.

beresp

The response received from the backend, one cache misses, the store object is built from beresp.

beresp

Type: HTTP

Readable from: vcl_backend_response, vcl_backend_error

The entire backend response HTTP data structure, useful as argument to VMOD functions.

beresp.body

Type: BODY

Writable from: vcl_backend_error

For producing a synthetic body.

beresp.proto VCL <= 4.0

Type: STRING

Readable from: vcl_backend_response, vcl_backend_error

Writable from: vcl_backend_response, vcl_backend_error

The HTTP protocol version the backend replied with.

beresp.proto VCL >= 4.1

Type: STRING

Readable from: vcl_backend_response, vcl_backend_error

The HTTP protocol version the backend replied with.

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 on the form XXYZZ can be set where XXYZZ is less than 65536 and Y is [1...9]. Only YZZ will be sent back to clients.

XX can be therefore be used to pass information around inside VCL, for instance return(synth(22404)) from vcl_recv{} to vcl_synth{}

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.http.*

Type: HEADER

Readable from: vcl_backend_response, vcl_backend_error

Writable from: vcl_backend_response, vcl_backend_error

Unsetable from: vcl_backend_response, vcl_backend_error

The HTTP headers returned from the server.

beresp.do_esi

Type: BOOL

Readable from: vcl_backend_response, vcl_backend_error

Writable from: vcl_backend_response, vcl_backend_error

Default: false

Set it to true to parse the object for ESI directives. Will only be honored if req.esi is true.

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.do_gzip

Type: BOOL

Readable from: vcl_backend_response, vcl_backend_error

Writable from: vcl_backend_response, vcl_backend_error

Default: false

Set to true to gzip the object while storing it.

beresp.do_gunzip

Type: BOOL

Readable from: vcl_backend_response, vcl_backend_error

Writable from: vcl_backend_response, vcl_backend_error

Default: false

Set to true to gunzip the object while storing it in the cache.

beresp.was_304

Type: BOOL

Readable from: vcl_backend_response, vcl_backend_error

When true this indicates that we got a 304 response to our conditional fetch from the backend and turned that into beresp.status = 200

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.

This may may produce 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.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.age

Type: DURATION

Readable from: vcl_backend_response, vcl_backend_error

The age of the object.

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.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.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.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.backend.ip

Type: IP

Readable from: vcl_backend_response

IP of the backend this response was fetched from.

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.

obj

This is the object we found in cache. It cannot be modified.

obj.proto

Type: STRING

Readable from: vcl_hit

The HTTP protocol version stored in the object.

obj.status

Type: INT

Readable from: vcl_hit

The HTTP status code stored in the object.

obj.reason

Type: STRING

Readable from: vcl_hit

The HTTP reason phrase stored in the object.

obj.hits

Type: INT

Readable from: vcl_hit, vcl_deliver

The count of cache-hits on this object.

In vcl_deliver a value of 0 indicates a cache miss.

obj.http.*

Type: HEADER

Readable from: vcl_hit

The HTTP headers stored in the object.

obj.ttl

Type: DURATION

Readable from: vcl_hit, vcl_deliver

The object's remaining time to live, in seconds.

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 grace period in seconds.

obj.keep

Type: DURATION

Readable from: vcl_hit, vcl_deliver

The object's keep period in seconds.

obj.uncacheable

Type: BOOL

Readable from: vcl_deliver

Whether the object is uncacheable (pass, hit-for-pass or hit-for-miss).

obj.storage

Type: STEVEDORE

Readable from: vcl_hit, vcl_deliver

The storage backend where this object is stored.

resp

This is the response we send to the client, it is built from either beresp (pass/miss), obj (hits) or created from whole cloth (synth).

With the exception of resp.body all resp.* variables available in both vcl_deliver{} and vcl_synth{} as a matter of symmetry.

resp

Type: HTTP

Readable from: vcl_deliver, vcl_synth

The entire response HTTP data structure, useful as argument to VMODs.

resp.body

Type: BODY

Writable from: vcl_synth

To produce a synthetic response body, for instance for errors.

resp.proto VCL <= 4.0

Type: STRING

Readable from: vcl_deliver, vcl_synth

Writable from: vcl_deliver, vcl_synth

The HTTP protocol version to use for the response.

resp.proto VCL >= 4.1

Type: STRING

Readable from: vcl_deliver, vcl_synth

Writable from: vcl_deliver, vcl_synth

The HTTP protocol version to use for the response.

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.

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.http.*

Type: HEADER

Readable from: vcl_deliver, vcl_synth

Writable from: vcl_deliver, vcl_synth

Unsetable from: vcl_deliver, vcl_synth

The HTTP headers that will be returned.

resp.do_esi VCL >= 4.1

Type: BOOL

Readable from: vcl_deliver, vcl_synth

Writable from: vcl_deliver, vcl_synth

Default: Set if ESI parsing has happened.

This can be used to selectively disable ESI processing, even though ESI parsing happened during fetch. This is useful when Varnish caches peer with each other.

resp.is_streaming

Type: BOOL

Readable from: vcl_deliver, vcl_synth

Returns true when the response will be streamed while being fetched from the backend.

Special variables

now

Type: TIME

Readable from: all

The current time, in seconds since the UNIX epoch.

When converted to STRING in expressions it returns a formatted timestamp like Tue, 20 Feb 2018 09:30:31 GMT

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.

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.