vmod_directors man page on DragonFly
[printable version]
VMOD_DIRECTORS(3) VMOD_DIRECTORS(3)
NAME
vmod_directors - Varnish Directors Module
SYNOPSIS
import directors [from "path"] ;
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 ini‐
tialize 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.
CONTENTS
· Object fallback
· VOID fallback.add_backend(BACKEND)
· BACKEND fallback.backend()
· VOID fallback.remove_backend(BACKEND)
· Object hash
· VOID hash.add_backend(BACKEND, REAL)
· BACKEND hash.backend(STRING_LIST)
· VOID hash.remove_backend(BACKEND)
· Object random
· VOID random.add_backend(BACKEND, REAL)
· BACKEND random.backend()
· VOID random.remove_backend(BACKEND)
· Object round_robin
· VOID round_robin.add_backend(BACKEND)
· BACKEND round_robin.backend()
· VOID round_robin.remove_backend(BACKEND)
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();
VOID round_robin.add_backend(BACKEND)
Prototype
VOID round_robin.add_backend(BACKEND)
Description
Add a backend to the round-robin director.
Example
vdir.add_backend(backend1); vdir.add_backend(backend2);
VOID round_robin.remove_backend(BACKEND)
Prototype
VOID round_robin.remove_backend(BACKEND)
Description
Remove a backend from the round-robin director.
Example
vdir.remove_backend(backend1); vdir.remove_backend(backend2);
BACKEND round_robin.backend()
Prototype
BACKEND round_robin.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();
VOID fallback.add_backend(BACKEND)
Prototype
VOID fallback.add_backend(BACKEND)
Description
Add a backend to the director.
Note that the order in which this is done matters for the fall‐
back director.
Example
vdir.add_backend(backend1); vdir.add_backend(backend2);
VOID fallback.remove_backend(BACKEND)
Prototype
VOID fallback.remove_backend(BACKEND)
Description
Remove a backend from the director.
Example
vdir.remove_backend(backend1); vdir.remove_backend(backend2);
BACKEND fallback.backend()
Prototype
BACKEND fallback.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();
VOID random.add_backend(BACKEND, REAL)
Prototype
VOID random.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);
VOID random.remove_backend(BACKEND)
Prototype
VOID random.remove_backend(BACKEND)
Description
Remove a backend from the director.
Example
vdir.remove_backend(backend1); vdir.remove_backend(backend2);
BACKEND random.backend()
Prototype
BACKEND random.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();
VOID hash.add_backend(BACKEND, REAL)
Prototype
VOID hash.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);
VOID hash.remove_backend(BACKEND)
Prototype
VOID hash.remove_backend(BACKEND)
Description
Remove a backend from the director.
Example
vdir.remove_backend(backend1); vdir.remove_backend(backend2);
BACKEND hash.backend(STRING_LIST)
Prototype
BACKEND hash.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
VMOD_DIRECTORS(3)
[top]
List of man pages available for DragonFly
Copyright (c) for man pages and the logo by the respective OS vendor.
For those who want to learn more, the polarhome community provides shell access and support.
[legal]
[privacy]
[GNU]
[policy]
[cookies]
[netiquette]
[sponsors]
[FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
....................................................................
|
|
Vote for polarhome
|
