1VCL-BACKENDS(7) VCL-BACKENDS(7)
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6 VCL-backends - Configuring Backends
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9 A backend declaration creates and initialises a named backend object.
10 A declaration start with the keyword backend followed by the name of
11 the backend. The actual declaration is in curly brackets, in a
12 key/value fashion.:
13 backend name {
15 .attribute1 = value;
16 .attribute2 = value;
17 [...]
18 }
19 If there is a backend named default it will be used unless another
21 backend is explicitly set. If no backend is named default the first
22 backend in the VCL program becomes the default.
23 If you only use dynamic backends created by VMODs, an empty, always
25 failing (503) backend can be specified:
26 backend default none;
28 A backend must be specified with either a .host or a .path attribute,
30 but not both. All other attributes have default values.
31
33 To specify a networked backend .host takes either a numeric IPv4/IPv6
34 address or a domain name which resolves to at most one IPv4 and one
35 IPv6 address:
36 .host = "127.0.0.1";
38 .host = "[::1]:8080";
40 .host = "example.com:8081";
42 .host = "example.com:http";
44
46 The TCP port number or service name can be specified as part of .host
47 as above or separately using the .port attribute:
48 .port = "8081";
50 .port = "http";
52
54 The absolute path to a Unix(4) domain socket of a local backend:
55 .path = "/var/run/http.sock";
57 A warning will be issued if the uds-socket does not exist when the VCL
59 is loaded. This makes it possible to start the UDS-listening peer, or
60 set the socket file's permissions afterwards.
61 If the uds-socket socket does not exist or permissions deny access,
63 connection attempts will fail.
64
66 A host header to add to probes and regular backend requests if they
67 have no such header:
68 .host_header = "Host: example.com";
70
72 These attributes control how patient varnishd is during backend
73 fetches:
74 .connect_timeout = 1.4s;
76 .first_byte_timeout = 20s;
77 .between_bytes_timeout = 10s;
78 The default values comes parameters with the same names, see var‐
80 nishd(1).
81
83 Limit how many simultaneous connections varnish can open to the back‐
84 end:
85 .max_connections = 1000;
87
89 Send a PROXY protocol header to the backend with the client.ip and
90 server.ip values:
91 .proxy_header = 2;
93 Legal values are one and two, depending which version of the PROXY pro‐
95 tocol you want.
96 Notice this setting will lead to backend connections being used for a
98 single request only (subject to future improvements). Thus, extra care
99 should be taken to avoid running into failing backend connections with
100 EADDRNOTAVAIL due to no local ports being available. Possible options
101 are:
102 • Use additional backend connections to extra IP addresses or TCP
104 ports
105 • Increase the number of available ports (Linux sysctl
107 net.ipv4.ip_local_port_range)
108 • Reuse backend connection ports early (Linux sysctl
110 net.ipv4.tcp_tw_reuse)
111
113 Send a BLOB on all newly opened connections to the backend:
114 .preamble = :SGVsbG8gV29ybGRcbgo=:;
116
118 Please see vcl-probe(7).
119
121 • varnishd(1)
122 • vcl(7)
124 • vcl-probe(7)
126 • vmod_directors(3)
128 • vmod_std(3)
130
132 VCL was developed by Poul-Henning Kamp in cooperation with Verdens Gang
133 AS, Redpill Linpro and Varnish Software. This manual page is written
134 by Per Buer, Poul-Henning Kamp, Martin Blix Grydeland, Kristian Lyn‐
135 gstøl, Lasse Karstensen and others.
136
138 This document is licensed under the same license as Varnish itself. See
139 LICENSE for details.
140 • Copyright (c) 2006 Verdens Gang AS
142 • Copyright (c) 2006-2021 Varnish Software AS
144 VCL-BACKENDS(7)