noble (7) vcl-backend.7.gz

NAME

       VCL-backends - Configuring Backends

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 {
              .attribute1 = value;
              .attribute2 = value;
              [...]
          }

       If  there  is  a  backend  named default it will be used unless another backend is explicitly set.  If no
       backend is named default the first backend in the VCL program becomes the default.

       If you only use dynamic backends created by  VMODs,  an  empty,  always  failing  (503)  backend  can  be
       specified:

          backend default none;

       A backend must be specified with either a .host or a .path attribute, but not both.  All other attributes
       have default values.

ATTRIBUTE .HOST

       To specify a networked backend .host takes either a numeric IPv4/IPv6 address  or  a  domain  name  which
       resolves to at most one IPv4 and one IPv6 address:

          .host = "127.0.0.1";

          .host = "[::1]:8080";

          .host = "example.com:8081";

       The TCP port number can be specified as part of .host as above or separately using the .port attribute:

          .port = 8081;

ATTRIBUTE .PATH

       The absolute path to a Unix(4) domain socket of a local backend:

          .path = "/var/run/http.sock";

       A warning will be issued if the uds-socket does not exist when the VCL is loaded.  This makes it possible
       to start the UDS-listening peer, or set the socket file's permissions afterwards.

       If the uds-socket socket does not exist or permissions deny access, connection attempts will fail.

ATTRIBUTE .HOST_HEADER

       A host header to add to probes and regular backend requests if they have no such header:

          .host_header = "Host: example.com";

TIMEOUT ATTRIBUTES

       These attributes control how patient varnishd is during backend fetches:

          .connect_timeout = 1.4s;
          .first_byte_timeout = 20s;
          .between_bytes_timeout = 10s;

       The default values comes parameters with the same names, see varnishd(1).

ATTRIBUTE .MAX_CONNECTIONS

       Limit how many simultaneous connections varnish can open to the backend:

          .max_connections = 1000;

ATTRIBUTE .PROXY_HEADER

       Send a PROXY protocol header to the backend with the client.ip and server.ip values:

          .proxy_header = 2;

       Legal values are one and two, depending which version of the PROXY protocol you want.

       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:

          • Use additional backend connections to extra IP addresses or TCP ports

          • Increase the number of available ports (Linux sysctl net.ipv4.ip_local_port_range)

          • Reuse backend connection ports early (Linux sysctl net.ipv4.tcp_tw_reuse)

ATTRIBUTE .PREAMBLE

       Send a BLOB on all newly opened connections to the backend:

          .preamble = :SGVsbG8gV29ybGRcbgo=:;

ATTRIBUTE .PROBE

       Please see vcl-probe(7).

SEE ALSO

       • varnishd(1)

       • vcl(7)

       • vcl-probe(7)

       • 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 others.

COPYRIGHT

       This document is licensed under the same license as Varnish itself. See LICENSE for details.

       • Copyright (c) 2006 Verdens Gang AS

       • Copyright (c) 2006-2021 Varnish Software AS

                                                                                                 VCL-BACKENDS(7)