#- # Copyright (c) 2013-2015 Varnish Software AS # All rights reserved. # # Author: Poul-Henning Kamp # # Redistribution and use in source and binary forms, with or without # modification, are permitted provided that the following conditions # are met: # 1. Redistributions of source code must retain the above copyright # notice, this list of conditions and the following disclaimer. # 2. Redistributions in binary form must reproduce the above copyright # notice, this list of conditions and the following disclaimer in the # documentation and/or other materials provided with the distribution. # # THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND # ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE # ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE # FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL # DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS # OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) # HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY # OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF # SUCH DAMAGE. $Module directors 3 Varnish Directors Module DESCRIPTION =========== `vmod_directors` enables backend load balancing in Varnish. The module implements a set of basic load balancing techniques, and also serves as an example on how one could extend the load balancing capabilities of Varnish. To enable load balancing you must import this vmod (directors). Then you define your backends. Once you have the backends declared you can add them to a director. This happens in executed VCL code. If you want to emulate the previous behavior of Varnish 3.0 you can just initialize the directors in vcl_init, like this:: sub vcl_init { new vdir = directors.round_robin(); vdir.add_backend(backend1); vdir.add_backend(backend2); } As you can see there is nothing keeping you from manipulating the directors elsewhere in VCL. So, you could have VCL code that would add more backends to a director when a certain URL is called. Note that directors can use other directors as backends. $Object round_robin() Description Create a round robin director. This director will pick backends in a round robin fashion. Example new vdir = directors.round_robin(); $Method VOID .add_backend(BACKEND) Description Add a backend to the round-robin director. Example vdir.add_backend(backend1); vdir.add_backend(backend2); $Method VOID .remove_backend(BACKEND) Description Remove a backend from the round-robin director. Example vdir.remove_backend(backend1); vdir.remove_backend(backend2); $Method BACKEND .backend() Description Pick a backend from the director. Example set req.backend_hint = vdir.backend(); $Object fallback() Description Create a fallback director. A fallback director will try each of the added backends in turn, and return the first one that is healthy. Example new vdir = directors.fallback(); $Method VOID .add_backend(BACKEND) Description Add a backend to the director. Note that the order in which this is done matters for the fallback director. Example vdir.add_backend(backend1); vdir.add_backend(backend2); $Method VOID .remove_backend(BACKEND) Description Remove a backend from the director. Example vdir.remove_backend(backend1); vdir.remove_backend(backend2); $Method BACKEND .backend() Description Pick a backend from the director. Example set req.backend_hint = vdir.backend(); $Object random() Description Create a random backend director. The random director distributes load over the backends using a weighted random probability distribution. Example new vdir = directors.random(); $Method VOID .add_backend(BACKEND, REAL) Description Add a backend to the director with a given weight. Each backend backend will receive approximately 100 * (weight / (sum(all_added_weights))) per cent of the traffic sent to this director. Example # 2/3 to backend1, 1/3 to backend2. vdir.add_backend(backend1, 10.0); vdir.add_backend(backend2, 5.0); $Method VOID .remove_backend(BACKEND) Description Remove a backend from the director. Example vdir.remove_backend(backend1); vdir.remove_backend(backend2); $Method BACKEND .backend() Description Pick a backend from the director. Example set req.backend_hint = vdir.backend(); $Object hash() Description Create a hashing backend director. The director chooses the backend server by computing a hash/digest of the string given to .backend(). Commonly used with ``client.ip`` or a session cookie to get sticky sessions. Example new vdir = directors.hash(); $Method VOID .add_backend(BACKEND, REAL) Description Add a backend to the director with a certain weight. Weight is used as in the random director. Recommended value is 1.0 unless you have special needs. Example vdir.add_backend(backend1, 1.0); vdir.add_backend(backend2, 1.0); $Method VOID .remove_backend(BACKEND) Description Remove a backend from the director. Example vdir.remove_backend(backend1); vdir.remove_backend(backend2); $Method BACKEND .backend(STRING_LIST) Description Pick a backend from the backend director. Use the string or list of strings provided to pick the backend. Example # pick a backend based on the cookie header from the client set req.backend_hint = vdir.backend(req.http.cookie); COPYRIGHT ========= This document is licensed under the same licence as Varnish itself. See LICENCE for details. * Copyright (c) 2013-2015 Varnish Software AS