7
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.
The following operators are available in VCL:
= Assignment operator.
+=, -=, *=, /= Assign and increment/decrement/multiply/divide operator.
For strings, += appends.
==, !=, <, >, <=, >= Comparisons
~, !~ Match / non-match. Can either be used with regular expressions or ACLs.
! Negation.
&& / || Logical and/or.
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.
These are the data types in Varnish. You can set or unset these.
Example:
set req.http.User-Agent = "unknown"; unset req.http.Range;
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 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 unset. This allows checks of the type if (req.http.opthdr) {} to test if a header exists, even if it is empty, whereas if (req.http.opthdr == "") {} does not distinguish if the header does not exist or if it is 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.
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 notion of the current time, which is kept consistent during VCL subroutine invocations, so during the execution of a VCL state subroutine (vcl_* {}), including all user-defined subroutines being called, now always returns the same value.
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
In string context they return a string with their value rounded to 3 decimal places and excluding the unit, e.g. 1.500.
Certain fields are integers, used as expected. In string context they return a string, e.g. 1234.
VCL understands real numbers. In string context they return a string with their value rounded to 3 decimal places, e.g. 3.142.
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$") {
...
}
To include a VCL file in another file use the include keyword:
include "foo.vcl";
The import statement is used to load Varnish Modules (VMODs.)
Example:
import std;
sub vcl_recv {
std.log("foo");
}
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.
*/
}
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";
}
One of the attributes .host or .path is mandatory (but not both). The attributes will inherit their defaults from the global parameters. The following attributes are available:
.host The host to be used. IP address or a hostname that resolves to a single IP address. This attribute is mandatory, unless .path is declared.
.path (VCL >= 4.1)
The absolute path of a Unix domain socket at which a backend is listening. If the file at that path does not exist or is not accessible to Varnish at VCL load time, then the VCL compiler issues a warning, but does not fail. This makes it possible to start the UDS-listening peer, or set the socket file’s permissions, after starting Varnish or loading VCL with a UDS backend. But the socket file must exist and have necessary permissions before the first connection is attempted, otherwise fetches will fail. If the file does exist and is accessible, then it must be a socket; otherwise the VCL load fails. One of .path or .host must be declared (but not both). .path may only be used in VCL since version 4.1.
.port The port on the backend that Varnish should connect to. Ignored if a Unix domain socket is declared in .path.
.host_header A host header to add to probes and regular backend requests if they have no such header.
.connect_timeout Timeout for connections.
Default: connect_timeout parameter, see varnishd
.first_byte_timeout Timeout for first byte.
Default: first_byte_timeout parameter, see varnishd
.between_bytes_timeout Timeout between bytes.
Default: between_bytes_timeout parameter, see varnishd
.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.
Notice this setting will lead to backend connections being used for a single request only (subject to future improvements). Thus, extra care should be taken to avoid running into failing backend connections with EADDRNOTAVAIL due to no local ports being available. Possible options are:
net.ipv4.ip_local_port_range)net.ipv4.tcp_tw_reuse).max_connections Maximum number of open connections towards this backend. If Varnish reaches the maximum Varnish it will start failing connections.
Empty backends can also be defined using the following syntax.:
backend name none;
An empty backend will always return status code 503 as if it is sick.
Backends can be used with directors. Please see the VMOD directors - Varnish Directors Module man page for more information.
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.
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);
}
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.
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;
}
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.
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 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_* {} subroutines 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 - Varnish Standard Module).
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.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
local.endpoint VCL >= 4.1
Type: STRING
Readable from: client, backend
The address of the ‘-a’ socket the session was accepted on.
If the argument was -a foo=:81 this would be “:81”
local.socket VCL >= 4.1
Type: STRING
Readable from: client, backend
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.
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 remote.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.
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.
req.grace
Type: DURATION
Readable from: client
Writable from: client
Upper limit on the object grace.
During lookup the minimum of req.grace and the object’s stored grace value will be used as the object’s grace.
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.is_hitmiss
Type: BOOL
Readable from: client
If this request resulted in a hitmiss
req.is_hitpass
Type: BOOL
Readable from: client
If this request resulted in a hitpass
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.
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.
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
Default: .connect_timeout attribute from the Backend definition, which defaults to the connect_timeout parameter, see varnishd.
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
Default: .first_byte_timeout attribute from the Backend definition, which defaults to the first_byte_timeout parameter, see varnishd.
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
Default: .between_bytes_timeout attribute from the Backend definition, which defaults to the between_bytes_timeout parameter, see varnishd.
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.
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.
More information in the HTTP response status section.
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.
It is a VCL error to use beresp.do_esi after setting beresp.filters.
beresp.do_stream
Type: BOOL
Readable from: vcl_backend_response, vcl_backend_error
Writable from: vcl_backend_response, vcl_backend_error
Default: true.
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.
This variable has no effect if do_esi is true or when the response body is empty.
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.
If http_gzip_support is disabled, setting this variable has no effect.
It is a VCL error to use beresp.do_gzip after setting beresp.filters.
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.
If http_gzip_support is disabled, setting this variable has no effect.
It is a VCL error to use beresp.do_gunzip after setting beresp.filters.
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
Default: Cache-Control s-maxage or max-age directives, or a value computed from the Expires header’s deadline, or the default_ttl parameter.
The object’s remaining time to live, in seconds.
beresp.age
Type: DURATION
Readable from: vcl_backend_response, vcl_backend_error
Default: Age header, or zero.
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
Default: Cache-Control stale-while-revalidate directive, or default_grace parameter.
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
Default: default_keep parameter.
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 VCL <= 4.0
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.
beresp.storage_hint VCL <= 4.0
Type: STRING
Readable from: vcl_backend_response, vcl_backend_error
Writable from: vcl_backend_response, vcl_backend_error
Deprecated since varnish 5.1 and discontinued since VCL 4.1 (varnish 6.0). Use beresp.storage instead.
Hint to Varnish that you want to save this object to a particular storage backend.
beresp.filters
Type: STRING
Readable from: vcl_backend_response
Writable from: vcl_backend_response
List of Varnish Fetch Processor (VFP) filters the beresp.body will be pulled through. The order left to right signifies processing from backend to cache, iow the leftmost filter is run first on the body as received from the backend after decoding of any transfer encodings.
VFP Filters change the body before going into the cache and/or being handed to the client side, where it may get processed again by resp.filters.
The following VFP filters exist in varnish-cache:
gzip: compress a body using gziptestgunzip: Test if a body is valid gzip and refuse it otherwisegunzip: Uncompress gzip contentesi: ESI-process plain text contentesi_gzip: Save gzipped snippets for efficient ESI-processing
This filter enables stitching together ESI from individually gzipped fragments, saving processing power for re-compression on the client side at the expense of some compression efficiency.
Additional VFP filters are available from VMODs.
By default, beresp.filters is constructed as follows:
gunzip gets added for gzipped content if beresp.do_gunzip or beresp.do_esi are true.esi_gzip gets added if beresp.do_esi is true together with beresp.do_gzip or content is already compressed.esi gets added if beresp.do_esi is truegzip gets added for uncompressed content if beresp.do_gzip is truetestgunzip gets added for compressed content if beresp.do_gunzip is false.After beresp.filters is set, using any of the beforementioned beresp.do_* switches is a VCL error.
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.
More information in the HTTP response status section.
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.
obj.can_esi
Type: BOOL
Readable from: vcl_hit, vcl_deliver
If the object can be ESI processed, that is if setting resp.do_esi or adding esi to resp.filters in vcl_deliver {} would cause the response body to be ESI processed.
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.
More information in the HTTP response status section.
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.
For the validation, first req.http.If-None-Match is compared against resp.http.Etag. If they compare equal according to the rules for weak validation (see RFC7232), a 304 is sent.
Secondly, req.http.If-Modified-Since is compared against resp.http.Last-Modified or, if it is unset, against the point in time when the object was last modified based on the Date and Age headers received with the backend response which created the object. If the object has not been modified based on that comparison, a 304 is sent.
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: obj.can_esi
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.
It is a VCL error to use resp.do_esi after setting resp.filters.
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.
resp.filters
Type: STRING
Readable from: vcl_deliver, vcl_synth
Writable from: vcl_deliver, vcl_synth
List of VDP filters the resp.body will be pushed through.
Before resp.filters is set, the value read will be the default filter list as determined by varnish based on resp.do_esi and request headers.
After resp.filters is set, changing any of the conditions which otherwise determine the filter selection will have no effiect. Using resp.do_esi is an error once resp.filters is set.
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
A session corresponds to the “conversation” that Varnish has with a single client connection, over which one or more request/response transactions may take place. It may comprise the traffic over an HTTP/1 keep-alive connection, or the multiplexed traffic over an HTTP/2 connection.
sess.xid VCL >= 4.1
Type: STRING
Readable from: client, backend
Unique ID of this session.
sess.timeout_idle
Type: DURATION
Readable from: client
Writable from: client
Idle timeout for this session, defaults to the timeout_idle parameter, see varnishd
sess.timeout_linger
Type: DURATION
Readable from: client
Writable from: client
Linger timeout for this session, defaults to the timeout_linger parameter, see varnishd
sess.send_timeout
Type: DURATION
Readable from: client
Writable from: client
Total timeout for ordinary HTTP1 responses, defaults to the send_timeout parameter, see varnishd
sess.idle_send_timeout
Type: DURATION
Readable from: client
Writable from: client
Send timeout for individual pieces of data on client connections, defaults to the idle_send_timeout parameter, see varnishd
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.
A status code normally has 3 digits XYZ where X must be between 1 and 5 included. Since it is not uncommon to see HTTP clients or servers relying on non-standard or even invalid status codes Varnish tolerates any status between 100 and 999.
With VCL code it is possible to use status codes in the form XXYZZ where the overall value is lower than 65536 and the Y digit is between 1 and 9 included. Only the YZZ part is sent to the client.
The XXYZZ form of status codes can be set on resp.status and beresp.status or passed via return(synth(...)) and return(error(...)) transitions.
XX can be therefore be used to pass information around inside VCL, for instance return(synth(22404)) from vcl_recv{} to vcl_synth{}.
The obj.status variable will inherit the XXYZZ form, but in a ban expresion only the YZZ part will be available. The XXYZZ form is strictly limited to VCL execution.
Assigning an HTTP standardized code to resp.status or beresp.status will also set resp.reason or beresp.reason to the corresponding status message.
The following built-in functions are available:
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>:
string fields:
req.url: The request urlreq.http.*: Any request headerobj.status: The cache object statusobj.http.*: Any cache object headerobj.status is treated as a string despite the fact that it is actually an integer.
duration fields:
obj.ttl: Remaining ttl at the time the ban is issuedobj.age: Object age at the time the ban is issuedobj.grace: The grace time of the objectobj.keep: The keep time of the object<operator>:
for all fields:
==: <field> and <arg> are equal!=: <field> and <arg> are unequalstrings are compared case sensitively
for string fields:
~: <field> matches the regular expression <arg>
!~:<field> does not match the regular expression <arg>
for duration fields:
>: <field> is greater than <arg>
>=: <field> is greater than or equal to <arg>
<: <field> is less than <arg>
<=: <field> is less than or equal to <arg>
<arg>:
for string fields:
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.
for duration fields:
A VCL duration like 10s, 5m or 1h, see Durations
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>.
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.
Prepare a synthetic response body containing the STRING. Available in vcl_synth and vcl_backend_error.
Identical to set resp.body / set beresp.body.
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.
As regsub(), but this replaces all occurrences.
For converting or casting VCL values between data types use the functions available in the std VMOD.
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 and 4.1.
For examples, please see the online documentation.
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 © 2006 Verdens Gang AS
Copyright © 2006–2020 Varnish Software AS
Licensed under the BSD-2-Clause License.
https://varnish-cache.org/docs/6.5/reference/vcl.html